See the Glossary of underwater diving terminology for definitions of technical terms, jargon, diver slang and acronyms used in underwater diving

See the Outline of underwater diving for a hierararchical listing of underwater diving related articles

See the Index of underwater divers for an alphabetical listing of articles about underwater divers

See the Index of recreational dive sites for an alphabetical listing of articles about places which are recreational dive sites

The following index is provided as an overview of and topical guide to underwater diving:

Underwater diving can be described as all of the following:

• A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.

1 – 9

• 14th CMAS Underwater Photography World Championship – 2013 photography competition held in Cuba
• 1973 Mount Gambier cave diving accident – Scuba cave diving incident in South Australia
• 1982 invasion of the Falkland Islands – Argentine invasion of the Falklands
• 1992 cageless shark-diving expedition – First recorded cageless dive with great white sharks
• 2011 Finswimming World Championships – 2011 swimming competition held in Hungary
• 2013 Finswimming World Championships – International competition in Kazan, Russia
• 2016 Finswimming World Championships – International competition in Volos, Greece
• 2018 Finswimming World Championships – International competition in Belgrade, Serbia
• 35-ton deep-submergence rescue vehicle – Chinese Navy submarine rescue submersible
• 8A4-class ROUV – Chinese work class remotely operated underwater vehicle

A

• AAI underwater revolver – Six-round amphibious revolver for naval use
• A Blueprint for Survival (cave diving) – Book on cave diving safety by Sheck Exley
• ABISMO – Japanese remotely operated underwater vehicle for deep sea exploration
• ABLJ – Configuration of diving buoyancy compensator
• Acoustic beacon – Device that emits a sound signal to aid location underwater
• Acoustic positioning system – System for tracking and navigation of underwater vehicles or divers using acoustic signals
• Active addition rebreather – Semi closed circuit rebreather type
• Adaptive Support Diver – Scuba diver trained to support divers with disabilities
• Administrative controls – Industrial safety
• ADS 2000 atmospheric diving system – US Navy armoured diving suit
• ADS amphibious rifle – Russian bullpup assault rifle for combat divers
• Advanced European Scientific Diver – A diver competent to organise a scientific diving team
• Advanced Open Water Diver – Recreational scuba diving certification slightly above minimum entry level
• Advanced open-water diver – Recreational scuba diving certification slightly above minimum entry level
• Advanced nitrox diver – Technical diving qualification to use multiple mixtures of oxygen enriched air
• Advanced SEAL Delivery System – Former Navy SEAL mini-sub deployed from submarines
• Advanced trimix diver – Recreational technical diving certification level
• Aerosinusitis – Barotrauma of the sinuses
• Aerospace Medical Association – Professional organization in aviation, space, hyperbaric and environmental medicine
• AIDA Hellas – National representative of AIDA International in Greece
• AIDA International (AIDA) – Worldwide rule- and record-keeping body for competitive breath-hold events
• Air embolism – Vascular blockage by air bubbles
• Airlift (dredging device), also known as air-lift – Dredging device using injected air to move water and entrained load up a pipe
• Airlift dredging – Removing underwater sediment using an airlift pump
• Air line – Tube or hose carrying a compressed air supply
• Air-line diving, also known as airline diving – Basic mode of surface-supplied underwater diving
• Airlock, also known as air-lock – Compartment for transfer between environments with different atmospheres
• Air lock diving bell – Type of mobile pressure caisson
• Air lock diving-bell plant – Underwater work support barge used at Gibraltar
• Air spread – The topside base for surface-supplied air diving operations
• Air top, also known as air top-up – Modifying or completing a gas blend by adding compressed air
• Alert Diver – Quarterly magazine published by DAN
• Algal bloom – Spread of planktonic algae in water
• Alpazat cave rescue – Six British soldiers trapped in a flooded Mexican cave
• Al-Sabehat – Iranian swimmer delivery vehicle
• Alternative air source – Emergency supply of breathing gas for an underwater diver
• Alternative air supply – Emergency supply of breathing air for an underwater diver
• Alternative gas supply – Emergency breathing gas supply
• Alternobaric vertigo – Dizziness resulting from unequal pressures in the middle ears
• Altitude decompression – Reduction in ambient pressure due to ascent above sea level
• Altitude diver – Diver competent to plan decompression at altitude
• Altitude Diver – Diver qualification for the skills to decompress at altitude
• Altitude diving – Underwater diving at altitudes above 300 m
• Aluminaut – First aluminum hulled submarine
• Ama (diving) – Japanese pearl divers
• Ambient pressure – Pressure of the surrounding medium
• American Academy of Underwater Sciences (AAUS) – American diving standards organisation
• American Canadian Underwater Certifications (ACUC) – Recreational diver training and certification agency
• American Nitrox Divers International (ANDI) – Recreational diver training and certification agency
• Amontons' law – Relationship between pressure and temperature of a gas at constant volume
• Anchor pattern – Arrangement of anchors allowing precise positioning of a vessel
• Anti-fog – Chemicals that prevent the condensation of water as small droplets on a surface
• Anti-frogman techniques – Methods of protection from incursions by divers and swimmers
• AN/WQX-2 – Diver detection sonar used in defense against underwater incursions
• Ankle strap (diving) – Staps worn over the ankles of dry suits to prevent the boots from pulling off when in use
• Ankle weights (diving) – Diver trim weights worn at the ankles
• ANMP – Association nationale des moniteurs de plongée
• ANSTI breathing simulator – Machine to measure work of breathing of diving apparatus
• ANSTI machine – Machine to measure work of breathing of diving apparatus
• Anti-fog – Chemicals that prevent the condensation of water as small droplets on a surface
• Anti-frogman techniques – Methods of protection from incursions by divers and swimmers
• Antipodes (submersible) – Commercial submarine built in 1973
• Anxiety – Unpleasant state of inner turmoil over anticipated events
• AP Diving – British manufacturer of underwater diving equipment
• Apeks – British manufacturer of scuba diving equipment
• Apnea blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
• Apnea finswimming, also known as Apnoea finswimming – Underwater swimming in a swimming pool using mask, monofin and holding one's breath.
• Apparent weight – Weight of an object when a force additional to gravity is present
• APS underwater rifle – Soviet underwater assault firearm firing unrifled steel flechettes
• Aqua Lung America – American company manufacturing recreational diving equipment
• Aqua Lung/La Spirotechnique – French company manufacturing breathing apparatus and diving equipment
• Aqua-Lung – Original name for open-circuit scuba equipment
• Aquanaut – Diver who remains at depth underwater for longer than 24 hours
• Aquarium diving – Occupational diving in large aquariums
• Aquascope – Underwater viewing device
• Aquathlon (underwater wrestling) – Competitive underwater wrestling
• Aqueon – Diver powered propulsion device
• Archaeological diving – Method in underwater archaeology
• Archaeology of shipwrecks – Study of human activity through the analysis of shipwreck artifacts
• Archimède – French Navy bathyscaphe
• Argox – Gas mixture occasionally used by scuba divers for dry-suit inflation
• Archimedes' principle – Buoyancy principle in fluid dynamics
• Army engineer diver – Armed forces occupation
• Army Ranger Wing – Special operations force of the Irish Defence Forces
• Artificial gills (human) – Hypothetical devices to extract oxygen from water
• Artificial reef – Human-made underwater structure that functions as a reef
• Artificial Reef Society of British Columbia (ARSBC) – Canadian non-profit to create artificial reefs for habitat enhancement and recreation
• AR vest – Type of jacket harness for surface-supplied diving
• Ascending and descending (diving) – Procedures for safe ascent and descent in underwater diving
• Ascent and descent (diving) – Procedures for safe ascent and descent in underwater diving
• Ascent blackout – Loss of consciousness caused by cerebral hypoxia on ascending from a deep freedive
• Ascents and descents (diving) – Procedures for safe ascent and descent in underwater diving
• Asphyxia – Severely deficient supply of oxygen
• Assisted ascent – An emergency ascent during which the diver is provided with breathing gas by another diver
• Association nationale des moniteurs de plongée – French recreational diver training and certification agency
• Association of Diving Contractors International (ADCI) – Non-profit organization for promoting standards and knowledge for commercial diving
• Atlantis ROV Team – High-school underwater robotics team from Whidbey Island, Washington, United States
• Atmospheric diving suit – Articulated pressure resistant anthropomorphic housing for an underwater diver
• ASM-DT amphibious rifle – Russian folding stock underwater firearm
• Association nationale des moniteurs de plongée (ANMP) – French recreational diver training and certification agency
• Atmospheric diving suit – Articulated pressure resistant anthropomorphic housing for an underwater diver
• Atmospheric diving system – Diving equiment that isolates the diver from ambient pressure
• Atmospheric pressure diving – Articulated pressure resistant housing for underwater diver
• Atmospheric suit diving – Diving in an articulated pressure resistant anthropomorphic housing
• Atmospheric pressure – Static pressure exerted by the weight of the atmosphere
• Atrial septal defect – Human heart defect present at birth
• Attitude (diver) – Alignment of the priciple axes of a diver in the water
• Australian Diver Accreditation Scheme (ADAS) – Australian based international occupational diver accreditation organisation
• Australian Submarine Rescue Vehicle Remora – Diving bell operated by the Australian Navy
• Australian Underwater Federation (AUF) – Governing body for underwater sports in Australia
• Auto-dump valve – Valve to release excess gas from a dry suit
• Automatic diluent valve – Demand valve to maintain volume of a rebreather loop
• Autonomous diver, also known as Autonomous Diver or Autonomous scuba diver – International minimum standard for entry level recreational scuba diver certification
• Autonomous Robotics Ltd – UK company developing an autonomous underwater vehicle
• Autonomous underwater vehicle – Unmanned underwater vehicle with autonomous guidance system
• AUV-150 – Unmanned underwater vehicle in development in by Central Mechanical Engineering Research Institute
• AUV Abyss – Autonomous underwater vehicle for mapping of the seabed and water column data collection
• Avascular necrosis – Death of bone tissue due to interruption of the blood supply

B

• Bachrach, Arthur J. – American psychologist and administrator (1923–2011)
• Back gas – Scuba breathing gas carried on the back of the diver
• Back kick (finning) – Finning technique to move backwards
• Back-mounted scuba – Scuba set carried on the diver's back
• Backplate and wing – Type of back-mount scuba harness
• Bail out to open circuit – Abort a rebreather dive and surface using open circuit scuba
• Bail-out cylinder – Emergency gas supply cylinder carried by a diver
• Bailout (diving) – To switch over to an emergency system during a dive
• Bailout block – Valve block on diver's equipment for switching between main and emergency gas supply
• Bailout bottle – Emergency gas supply cylinder carried by a diver
• Bailout gas – Emergency breathing gas supply carried by the diver
• Bailout rebreather – Diving rebreather carried as an emergency gas supply
• Bailout set – Emergency gas supply scuba carried by a diver
• Bailout system – System to provide emergency breathing gas to a diver
• Bailout to open circuit – Abort a rebreather dive and surface using open circuit scuba
• Bailout valve – Valve opening the supply of emergency breathing gas
• Bailout valve (rebreather) – Valve on rebreather mouthpiece to switch to emergency gas supply
• Baited remote underwater video – Equipment for estimating fish populations
• Band mask – Heavy duty full-face diving mask for surface-supplied diving
• Barodontalgia – Tooth pain caused by ambient pressure change
• Barostriction – Obstruction of pressure equalization passages
• Barotrauma – Injury caused by pressure
• Barotrauma of ascent – Injuries caused by a reduction in ambient pressure
• Barotraumas of decompression – Injuries caused by a reduction in ambient pressure
• Barton, Otis – American diver and actor (1899–1992)
• Basic Cave Diving: A Blueprint for Survival – Book on cave diving safety by Sheck Exley
• Basic life support – Emergency medical care by first responder
• Bathyscaphe – Free-diving self-propelled deep-sea submersible
• Beebe, William – American ornithologist, marine biologist, entomologist, and explorer (1877–1962)
• Behnke, Albert R. – US Navy physician and diving medicine researcher
• Belize Barrier Reef – Series of coral reefs straddling the coast of Belize
• Bell bounce diving – Surface oriented diving using a closed bell
• Bell cursor – Device to guide and control a diving bell near and above the surface
• Bell gas panel – Group of hoses and cables provifing services to a diving bell
• Bell harness – Underwater diving safety haeness
• Bell stage – Platform below the chamber of a closed diving bell
• Bell umbilical – Bundle of hoses and cables providing services to a diving bell
• Bell-bounce dive – Surface-oriented diving in a closed bell
• Bellman (diver) – Diver working as standby diver and umbilical attendant from a diving bell
• Bellman (diving) – The member of a dive team who acts as stand-by diver and tender from the diving bell
• Benign water – Diving environment with very low risk
• Benign water diving – Diving in environments of low risk
• Bering Sea Gold – Television series
• Bering Sea Gold: Under The Ice – RedirectPages displaying short descriptions with no spaces
• Bert, Paul – French zoologist, physiologist and politician (1833–1886)
• Beuchat – French manufacturer of underwater diving equipment
• Bifin – Swimfin type with single foot pocket
• Biological hazard – Biological material that poses serious risks to the health of living organisms
• Black-water (diving) – Oceanic mid-water at night
• Black-water diving – Open ocean mid-water diving at night
• Blackout of ascent – Loss of consciousness caused by cerebral hypoxia on ascending from a deep freedive
• Blood–air barrier – Membrane separating alveolar air from blood in lung capillaries
• A Blueprint for Survival (cave diving) – Cave diving safety manual by Sheck Exley
• Blauhöhle – Flooded cave system in Southern Germany
• Blood shift – Set index article
• Blood shift (diving) – Blood flow to the extremities redistributed to the head and torso during a breathhold dive
• Blood–air barrier – Membrane separating alveolar air from blood in lung capillaries
• Błotniak – One-man wet cabin underwater craft designed in Poland in 1978
• Blue Grotto (Malta) – Sea caverns in Malta
• Blue hole – Marine cavern or sinkhole, open to the surface, in carbonate bedrock
• Blue Hole (New Mexico) – Sinkhole used for scubadiving in New Mexico, United States
• Blue Hole (Red Sea) – Submarine sinkhole north of Dahab, Egypt
• Blue Lake (Utah) – Large geothermal pond in Utah, U.S.
• Blue water diving – Diving in mid-water where the bottom is out of sight
• Blue-water (diving) – Oceanic mid-water
• Blue-water diving – Underwater diving in oceanic mid-water where the bottom is not visible and is out of diving range
• Boarding stirrup – A suspended step to help divers lift themselves from the water into a boat
• Boat diving – Procedures specific to diving from boats
• Boaty McBoatface – British autonomous underwater vehicle
• Bolt snap – Sprung slide gated snap hook
• Bond, George F. – US Navy physician and diving medicine and saturation diving researcher
• Booster pump – Machine to increase pressure of a fluid
• Bottom gas – Gas breathed during the deep part of a dive
• Bottom time – The elapsed time of a dive from starting the descent to starting the final ascent to the surface
• Bottom timer – An electronic instrument that records depth and elapsed time data on an underwater dive
• Boyle, Robert – Anglo-Irish scientist (1627–1691)
• Boyle's law – Relation between gas pressure and volume
• Boyle, Robert – Anglo-Irish scientist (1627–1691)
• Bradner, Hugh – American physicist, neoprene wetsuit inventor (1915–2008)
• Brazilian commando frogmen – GRUMEC is the special forces unit of the Brazilian Navy
• Breaking wave, also known as surf – Wave that becomes unstable as a consequence of excessive steepness
• Breath-hold blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
• Breathing – Process of moving air in and out of the lungs
• Breathing air – Air quality suitable for safe breathing
• Breathing air compressor – Machine that compresses atmospheric air at breathing gas quality
• Breathing apparatus – Equipment allowing or assisting the user to breath in a hostile environment
• Breathing gas – Gas used for human respiration
• Breathing gas analysis – Detection and measurement of components of a breathing gas
• Breathing gas quality – Purity requirements for gases for human breathing
• Breathing gas reclaim system – Equipment to recover helium based breathing gas after use by divers
• Breathing gas switch – Changing between breathing gasses of different composition while diving
• Breathing loop – Breathing gas circuit in a rebreather
• Breathing performance of regulators – Measurement and requirements of function of breathing regulators
• Breathing set – Equipment allowing or assisting the user to breath in a hostile environment
• Breathing tube (breathing apparatus) – Tube through which to breath ambient pressure air
• Briggs Marine – A marine services company based in the United Kingdom
• British commando frogmen – Special Boat Service, whose members are drawn largely from the Royal Marines
• British Divers Marine Life Rescue – United Kingdom charity organisation
• British Freediving Association (BFA) – British affiliate to AIDA International
• British Octopush Association (BOA) – National body for underwater hockey in the United Kingdom
• British Sub-Aqua Club (BSAC) – Recreational diving club, training and certification agency based in the UK
• British Underwater Sports Association (BUSA) – British affiliate to the world underwater federation sports committee.
• Brubakk, Alf O. – Norwegian decompression researcher (1941–2022)
• BRUV – Video system for estimating fish populations
• BSAC First Class Diver – Recreational diver competent to lead a group of dives carrying out a project
• BSAC London Branch – Original British Sub-Aqua Club branch
• Buddy bottle – Alternative name for scuba bailout set
• Buddy breathing – Technique for sharing breathing gas from a single mouthpiece
• Buddy check – Pre-dive safety checks carried out by two-diver dive teams
• Buddy diver – Person diving by the buddy system
• Buddy diving – Practice of mutual monitoring and assistance between two divers
• Buddy line – A tether between two scuba divers to prevent separation in low visibility
• Bühlmann, Albert A. – Swiss physician and decompression researcher (1923–1994)
• Bühlmann decompression algorithm, also known as Buhlmann algorithm – Mathematical model of tissue inert gas uptake and release with pressure change
• Bühlmann decompression model – Mathematical model of tissue inert gas uptake and release with pressure change
• Built-in breathing set – System for supply of breathing gas on demand within a confined space
• Built-in breathing system (BIBS) – System for supply of breathing gas on demand within a confined space
• Built-in breathing system regulator – Hyperbaric chamber breathing regulators that exhaust externally
• Buoyancy – Upward force that opposes the weight of an object immersed in fluid
• Buoyancy compensator (BCD), also known as buoyancy control device – Equipment for controlling the buoyancy of a diver
• Buoyancy compensator inflation hose – Inflation gas supply hose on scuba regulator
• Buoyancy control (disambiguation)
• Buoyancy control in scuba diving, also known as buoyancy control (scuba) – Essential safety skill
• Buoyancy control equipment – Diving equipment primarily intended to modify buoyancy of the diver
• Buoyant ascent – Type of emergency ascent in diving
• Byford Dolphin – Semi-submersible offshore drilling rig
• Byford Dolphin diving bell accident – Explosive decompression of an occupied saturation chamber
• Burst disc, also known as rupture disc – Non-closing over-pressure relief device

C

• Caisson (engineering) – Rigid structure to provide workers with a dry working environment below water level
• Cam band, also known as camband, cam strap, or camstrap – Strap with locking buckle to hold scuba cylinder on BCD harness
• Canadian Armed Forces Divers – Underwater divers employed by any of the Canadian armed forces
• Canister light – Dive light with battery pack and light head connected by cable
• Canoe and kayak diving – Recreational diving from a canoe or kayak
• Canoe diving – Recreational diving from a canoe
• Capernwray Dive Centre – Flooded quarry in Lancashire, England, used as a recreational dive site
• Carbon dioxide retention – A tendency to retain abnormally high tissue carbon dioxide levels
• Carbon dioxide scrubber – Device which absorbs carbon dioxide from circulated gas
• Carbon dioxide scrubbing reaction – Chemical reactions that remove carbon dioxide from air
• Carbon monoxide poisoning – Toxic effects of carbon monoxide
• Carleton CDBA – Military rebreather by Cobham plc
• Carmellan Research – British manufacturer of diving rebreathers
• Cascade filling system – Filling pressurized gas from a series of storage cylinders
• Cascade storage system – High pressure gas storage system set up for cascade filling
• Cave Divers Association of Australia (CDAA) – Association to represent cave divers and administrate and support cave diving in Australia
• Cave diving – Diving in water-filled caves
• Cave Diving Group (CDG) – UK based cave diver training and certification agency
• Cave diving regions – Geographical distribution of cave diving venues
• Cave diving regions of the world – Regions of the world where known cave diving venues exist
• Cave line – Line used for navigation in flooded caves
• Cave reel – Line holder used to lay and recover guideline in caves
• Cavern diver – Certification for diving under a natural overhead within the zone of natural light
• Cavern diving – Diving in the part of a cave where the exit is visible by natural light
• C-card – Certification as competent to dive to a specified standard
• C.E. Heinke & Co. Ltd. – British manufacturer of diving equipment
• Cenote – Natural pit or sinkhole that exposes groundwater underneath
• Center for Maritime Archaeology and Conservation – Academic centre at Texas A&M University
• Central nervous system oxygen toxicity – Adverse effects of exposure to a high partial pressure of oxygen
• Cerberus (sonar) – Diver detection device
• HMS Challenger K07 – Royal Navy saturation diving support vessel
• Chamber operation – Operation of a hyperbaric chamber in support of underwater diving
• Chamber operator – A person who operates a diving chamber
• Charles's law – Relationship between volume and temperature of a gas at constant pressure
• Chase boat – A tender generally not carried by the main vessel
• Checklist – Aide-memoire to ensure consistency and completeness in carrying out a task
• Chemical hazard – Non-biological hazards of hazardous materials
• Christmas tree ladder – Ladder with rungs cantilevered from a central rail
• Circular search – A search pattern where the diver swims at a series of distances around a fixed reference point
• Circulatory system – Organ system for circulating blood in animals
• Cis-Lunar – Manufacturer of electronically controlled closed-circuit rebreathers for scuba diving
• Civil liability in recreational diving – Legal duty of care, negligence and liability in recreational diving
• Clarke, John R. – American scientist and underwater breathing apparatus authority
• Classification of underwater activities – Classification of underwater diving activities by occupational field
• Cleaning and disinfection of personal diving equipment – Prevention of infection by shared or contaminated equipment
• Clearance diver – Navy diver specialist with explosives
• Clearance Divers Life Support Equipment (CDLSE) – British military electronically controlled closed circuit rebreather
• Clearance diving – Military diving work involving underwater demolition and work with explosives
• Clearance Diving Branch (RAN) – Diving unit of the Royal Australian Navy
• Clip-on weight – Small weights used to make fine adjustments to a diver's ballast
• Closed bell – Hyperbaric chamber for transporting divers vertically through the water
• Closed circuit breathing apparatus, also known as closed-circuit breathing apparatus – Apparatus to recycle breathing gas
• Closed circuit scuba – Self contained underwater breathing apparatus which recycles exhaled breathing gas
• Closed diving bell – Hyperbaric chamber for transporting divers vertically through the water
• Closed circuit bailout – Emergency gas supply from an independent closed circuit rebreather
• Closed-circuit oxygen rebreather – Apparatus to recycle breathing gas
• Clump weight – A heavy weight suspended on cable used to guide a diving bell
• CMAS* scuba diver – Entry level recreational diving certification from CMAS
• CMAS** scuba diver, also known as CMAS two-star scuba diver – Autonomous recreational scuba diving certification
• CMAS*** scuba diver – Fully trained and experienced recreational dive
• CMAS**** scuba diver – A three-star diver with a high level of competence and broad experience
• CMAS Europe – Non-profit branch of the world underwater federation representing European affiliates
• CMAS Scientific Committee – International organisation for underwater activities
• Code of practice – Set of written rules which specifies how people working in a particular occupation should behave
• Code of Practice for Scientific Diving: Principles for the Safe Practice of Scientific Diving in Different Environments – Document published by UNESCO
• Cold shock response – Physiological response to sudden exposure to cold
• Cold-water diving – Underwater diving in water that is cold enough to require special equipment
• Comando Raggruppamento Subacquei e Incursori Teseo Tesei – Italian special forces diving unit
• Combat Rubber Raiding Craft – Rubberised fabric tactical inflatable boat used by the US Navy
• Combat sidestroke – Variation of side-stroke swimming used by United States Navy SEALs
• Combined gas law – Combination of Charles', Boyle's and Gay-Lussac's gas laws
• Comex therapeutic table CX 30, also known as Comex 30 table – A hyperbaric treatment schedule developed by Comex
• Comhairle Fo-Thuinn (CFT) – Governing body for recreational diving and underwater hockey in Ireland
• Commandos Marine – Special operations forces of the French Navy
• Commandos Military Unit – Polish special operations unit
• Commercial diver registration in South Africa – Registration of commercial divers by the South African Department of Employment andLabour
• Commercial diver training – Underwater diving where divers are trained for their work
• Commercial diving – Professional diving on industrial projects
• Commercial diving school – Place where commercial diving skills are trained and assessed
• Commercial offshore diver – Professional diver working offshore
• Commercial offshore diving – Professional diving in support of the oil and gas industry
• Communications panel – Surface control panel for underwater diving voice communications system
• Compagnie maritime d'expertises – French offshore diving contractor
• Compass grid search – Technique for finding underwater targets
• Compass search – Search patterns controlled by compass directions
• Competence (human resources) – Ability of a person to do a job properly
• Competitive apnea – Competitive breathhold diving
• Competitive freediving – Breathold diving competition disciplines
• Competitive spearfishing – Hunting of fish underwater on breath-hold using a hand-loaded spear
• Compressed air – Air under a pressure greater than atmospheric
• Compression arthralgia – Joint pain caused by fast compression to high ambient pressure
• Compressor diving – Crude surface-supplied diving using unregulated air from an industrial low-pressure air compressor
• Compressor operator – Person competent to operate a diving air compressor
• Concentration – Ratio of part of a mixture to the whole
• Concentration gradient – Variation of concentration of a component of a mixture over distance
• Confédération Mondiale des Activités Subaquatiques (CMAS) – International organisation for underwater activities
• Confined water (diving) – A diving environment that is enclosed and bounded sufficiently for safe training
• Confined water diving – Diving in water which is enclosed and limited in extent
• Conservatism (diving) – Approach to risk reduction for decompression
• Constant flow regulator – Gas pressure control regulator which provides a calibrated output
• Constant mass flow regulator – Gas pressure regulator with a constant mass flow delivery
• Constant weight apnea – Freediving discipline in which the diver descends and ascends only by swimming, with or without fins
• Constant weight bi-fins – Competitive freediving discipline
• Constant weight without fins – Freediving discipline
• Contaminated water – Water containing high levels of hazardous materials
• Continental Shelf Station Two – Undersea research habitat in the Red Sea
• Contingency plan – A plan in case something unexpected occurs
• Continuous blending and compression – Gas blending by constant flow mixing and analysis
• Continuous guide line, also known as continuous guideline – Cord that can lead a scuba diver to open water
• Controlled buoyant lift – A technique used by scuba divers to raise an incapacitated diver to the surface
• Controlled emergency swimming ascent (CESA) – Technique used by scuba divers to return to the surface in an out-of-gas emergency in shallow water
• Coral reef – Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons
• Coral Reef Alliance – Non-profit, environmental NGO
• Coral reef protection – Modifying human activities to reduce impact on coral reefs.
• Corselet (diving helmet) – Part of a diving helmet supported by the shoulders
• Cosmos CE2F series – Italian swimmer delivery vehicles
• Counterlung – Variable volume component in a rebreather to take up and release gas during a breathing cycle
• Cracking pressure – Pressure difference over the diaphragm needed to open a demand valve
• Cramp – Pathological, often painful, involuntary muscle contraction
• Cressi-Sub – Italian manufacturer of recreational diving and swimming equipment.
• Crewed submersible – Small watercraft able to navigate under water
• Critical flicker fusion frequency – Concept in the psychophysics of vision
• Cryogenic rebreather – Rebreather that removes CO2 by freezing it out using heat exchange with liquid oxygen
• CUMA – Canadian military diving rebreather
• Current (hydrology) – Flow of water in a stream caused by gravity
• Current shear – Variation of flow rate transverse to flow direction
• Current (stream) – Flow of water in a stream caused by gravityPages displaying short descriptions of redirect targets
• CURV – Early remotely operated underwater vehicle
• Cylinder band – Straps to clamp two scuba cylinders together
• Cylinder pressure gauge – Instrument for measuring gas pressure in a storage cylinder
• Cylinder valve (disambiguation)

D

• Dacor (scuba diving) – Former American diving equipment manufacturer
• Dalton's law – Empirical law of partial pressures
• The Darkness Beckons – History of UK cave diving by Martyn Farr
• Damant, Guybon Chesney Castell – English physiologist, diver, royal navy officer, and researcher
• DAN Asia-Pacific – Regional organisation of the Divers Alert Network
• DAN Brasil – Regional organisation of the Divers Alert Network
• DAN Europe – Regional organisation of the Divers Alert Network
• DAN Japan – Regional organisation of the Divers Alert Network
• DAN Southern Africa – Regional organisation of the Divers Alert Network
• DAN World – Organisation of the Divers Alert Network covering other regions
• Darwin's Arch – Rock arch near Darwin Island (collapsed 2021)
• Davis Submerged Escape Apparatus – Early submarine escape oxygen rebreather also used for shallow water diving.
• Davis, Robert – English inventor and manufacturer of underwater breathing apparatus
• Day, John – First recorded death in a diving chamber
• D-BRUV – Downward looking baited remote underwater video
• DDRC Healthcare – British hyperbaric medical organisation
• Dead space (physiology) – Inhaled air not part of gas exchange
• Deadspace (in breathing apparatus) – Inhaled air not part of gas exchange
• Deadweight anchor – Anchor that relies on weight and friction for holding
• Deane, Charles Anthony – Pioneering diving engineer and inventor of a surface supplied diving helmet
• Decima Flottiglia MAS – Italian naval commando frogman unit of the Fascist era
• Deck decompression chamber – Hyperbaric chamber suitable for surface decompression or emergency use at a dive site
• Decompression algorithm – Procedure to calculate the decompression needed for a given dive profile
• Decompression bar – Horizontal bar suspended below the water surface at a decompression stop
• Decompression buoy – Inflatable surface marker buoy deployed from underwater
• Decompression chamber operation – Operation of a hyperbaric chamber in support of underwater diving
• Decompression computer – Instrument to calculate decompression status in real time
• Decompression cylinder – Scuba cylinder carrying decompression gas
• Decompression (diving) – Pressure reduction and its effects during ascent from depth
• Decompression equipment – Equipment used by divers to facilitate decompression
• Decompression gas – Oxygen-rich gas used for accelerated decompression
• Decompression illness – Disorders arising from ambient pressure reduction
• Decompression model – Conceptual explanation forf decompression that helps formulate predictions
• Decompression modelling – Using conceptual explanation forf decompression to help formulate predictions
• Decompression monitoring equipment – Equipment for monitoring depth and run time of a dive, and decompression status
• Decompression obligation – Physiological requirement for decompression to reduce risk of injury
• Decompression practice – Techniques and procedures for safe decompression of divers
• Decompression schedule – A specified ascent rate and series of increasingly shallower decompression stops
• Decompression sickness – Disorder caused by dissolved gases forming bubbles in tissues
• Decompression status – The theoretical level of inert gas content of the body tissues
• Decompression stop – Pause needed during the ascent from a dive
• Decompression stress – Combined influences on formation of decompression gas bubbles
• Decompression theory – Theoretical modelling of decompression physiology
• Decompression trapeze – Horizontal bars suspended at decompression stop depths
• Deep air diving – Underwater diving beyond accepted limits for breathing air
• Deep air diving blackout – Loss of consciousness due to extreme nitrogen narcosis
• DeepC – Autonomous underwater vehicle powered by a fuel cell
• Deep Diver – Research submersible
• Deep diving – Underwater diving to a depth beyond the norm accepted by the associated community
• Deep Drone – US Navy remotely operated underwater vehicle
• DeepFlight Merlin – 3-seater wet sub diver propulsion vehicle
• Deepsea Challenger – Bathyscaphe designed to reach the bottom of Challenger Deep
• Deepspot – Deep swimming pool in Poland
• Deep-submergence rescue vehicle – Submersible used for rescue of downed submarines and clandestine missions
• Deep water blackout (disambiguation)
• Deep water submersible – Self-propelled deep-diving crewed submersible
• Defence Diving School – Diver training centre in Hampshire, UK
• Defense against swimmer incursions – Methods of protection from incursions by divers and swimmers
• Delta-P (hazard) – Underwater hazard due to horizontal pressure differential
• Demand helmet – Diving helmet supplied with gas through a demand valve
• Demand valve oxygen therapy – Use of high inhalation concentrations of oxygen as medical treatment
• Demister (scuba) – Surfactant applied to prevent the condensation of water as droplets on a mask or helmet viewport
• Demobilise (diving) – The dismantling, packing and transport back to storage of the dive spread
• Demographics of recreational diving – Population distribution of recreational divers
• Demographics of scientific divers – Population distribution of scientific divers
• Denayrouze, Auguste – French inventor of a demand air supply regulator for underwater diving
• Dental barotrauma – Damage to a tooth caused by a change of ambient pressure
• Department of Employment and Labour – Department of the South African government responsible for matters related to employment
• Depth blackout – Loss of consciousness due to deep diving while breathing air
• Depth gauge – Instrument that indicates depth below a reference surface
• DEPTHX – Autonomous underwater vehicle for exploring sinkholes in Mexico
• Descending and ascending (diving) – Procedures for safe ascent and descent in underwater diving
• DESCO – American manufacturer of commercial diving equipment
• Developed pressure – Working pressure corrected for actual temperature
• Diamond Reef System – System for training divers in buoyancy, trim and maneuvering skills
• Diffuser (breathing set part) – Component fitted over the exhaust outlet to break up the exhaled gas
• Diffusion – Transport of dissolved species from the highest to the lowest concentration region
• Diluent flush – Rebreather diving safety procedure
• Diluent gas – Metabolically inert gas in a breathing mixture
• DIN 7876 – German standard for manufacture of swimfins
• Directed search – Searches directed from the surface
• Disappearance of Ben McDaniel – Scuba diver who disappeared during or after a cave dive
• Distance line/dive reel/guide line – Line deployed by scuba divers for navigation
• Diuresis – Increase in urine production
• Dive boat – Boat used for the support of scuba diving operations
• Dive boat operation – Operational procedures for a boat supporting diving
• Dive boat skipper – Person in command of a dive boat
• Dive briefing – Meeting of the dive team to discuss details before the diving operation
• Dive center – Service organisation providing recreational diver training, equipment and dive outings
• Dive computer, also known as Decompression computer – Instrument to calculate decompression status in real time
• Dive cylinder – Cylinder to supply breathing gas for divers
• Dive guide (disambiguation)
• Dive guide (publication) – Travel guides for recreational diving
• Dive leader – Recreational diving certification and role
• Dive Leader – Recreational diving certification
• Dive light – Light used underwater by a diver
• Dive log – Record of diving history of an underwater diver
• Divemaster – Recreational dive leader certification and role
• Dive planning – The process of planning an underwater diving operation
• Dive profile – Diver's pressure exposure over the time of a dive
• Dive school – Establishment for diver training
• Dive skins – Thin exposure suit to protect the skin in warm water
• Dive spool – Simple flanged cylindrical line-holder
• Dive suit – Garment or device designed to protect a diver from the underwater environment
• Dive supervisor – Professional diving team leader responsible for safety
• Dive Supervisor – Recreational dive leadership certification
• Dive tables – Data used to determine a decompression schedule for a given dive profile and breathing gas
• Dive team – A group of people working together to enhance dive safety and achieve a task
• Dive timer – Electronic timer that automatically records the run time of a dive
• Dive weights – Ballast weights carried by divers to counteract buoyancy of equipment
• Dive-float – Small buoy towed by an underwater diver to indicate presence
• Dive supervision – The work of the manager of a professional diving team
• Dive/surface valve – Valve on a rebreather mouthpiece to isolate the breathing loop when not in use
• Diver, The – Sculpture by John Kaufman
• Diver (United States Navy) – US Navy personnel qualified in underwater diving and salvage
• Diver certification – Certification as competent to dive to a specified standard
• Diver certification agency – Organisation which issues certification for competence in diving skills
• Diver certification equivalences – Comparison between certifications by different agencies
• Diver certification organisation – Organisation that issues certificates of competence to underwater divers
• Diver communications – Methods used by underwater divers to communicate
• Diver detection sonar – Acoustic location systems to detect divers and submerged swimmer delivery vehicles
• Diver down flag – Flag signal indicating divers are in the water nearby
• Diver hand signals – Hand signals used for communication with divers
• Diver lift – Movable platform for lifting a diver from the water to deck level
• Diver medical technician – Paramedic with special training in diving medical emergencies
• Diver navigation – Underwater navigation by scuba divers
• Diver organisations – Memberhip organisations of underwater divers
• Diver propulsion vehicle – Powered device for diver mobility and range extension (DPV)
• Diver rescue – Rescue of a distressed or incapacitated diver
• Diver safety – Risk management by and for the diver
• Diver searches – Underwater searches carried out by divers.
• Diver surface detection aids – Equipment to make a surfaced diver easier to find
• Diver training – Processes to develop the skills and knowledge to dive safely underwater
• Diver training manual – Documentary training aid used for training underwater divers
• Diver training organization – Organization which provides training in diving skills or knowledge
• Diver training organizations – Organization which provides training in diving skills or knowledge
• Diver training standard – Document describing requirements of a diver training programme
• Diver training tank – Tank of water to practice diving skills
• Diver trim – Balance and orientation skills of an underwater diver
• Diver voice communications – Protocol for spoken communications in diving operations
• Diver weighting system – Ballast carried by underwater divers to counteract buoyancy
• Diver weighting systems – Ballast carried by underwater divers to counteract buoyancy
• Diver's air pump – Manually powered surface air supply for divers
• Divers Academy International – Technical educational institution in New Jersey that offers training in commercial diving
• Divers Alert Network (DAN) – International group of not-for-profit organizations for improving diving safety
• Divers Alert Network America – A not-for-profit diving safety organization based in the US
• Divers Alert Network Asia-Pacific – A not-for-profit diving safety organization based in Australia
• Divers Alert Network Europe – A not-for-profit diving safety organization based in Europe
• Divers Alert Network publications
• Divers Alert Network Southern Africa – A public benefit diving safety organization based in South Africa
• Diver's attendant – Assistant for a diver
• Diver's cutting tool – A tool to assist in extricating the diver from entrapment by lines or nets
• Diver's harness – Item fastened around a diver which allows the diver to be lifted
• Divers Institute of Technology – Private, commercial educational institution for the training of commercial divers
• Diver's knife – A tool to assist in extricating the diver from entrapment by lines or nets
• Diver's logbook – Record of diving history of an underwater diver
• Diversnight – Annual recreational night diving festival.
• Diver's pump – Manually powered surface air supply for divers
• Diver's telephone – Hard wired diver communications equipment
• Diver's tender – Assistant to a diver
• Diver's umbilical – A hose and cable bundle which supplies breathing gas, communications and other services to a diver
• Divex – Scottish provider of diving equipment and related services.
• Diviac – Online booking site for diving holidays
• Diving accident – Accident occurring while diving underwater
• Diving activities – Things people do while diving underwater
• Diving air compressor, also known as Diving compressor – Machine used to compress breathing air for use by underwater divers
• Diving air compressor operator – Person who operates a diving air compressor
• Diving air filter – Device to purify compressed breathing air
• Diving air pump – Manually powered surface air supply for divers
• Diving attendant – Member of a dive team responsible for assisting the diver
• Diving basket – Platform for lowering and lifting a diver through the water
• Diving bell – Chamber for transporting divers vertically through the water
• Diving boat – Boat used for the support of scuba diving operations
• Diving buddy – Diver who dives as one of a buddy pair
• Diving certification – Evidence of having been trained to a standard
• Diving chamber – Hyperbaric pressure vessel for human occupation used in diving operations
• Diving chamber operation – Operation of a hyperbaric chamber in support of underwater diving
• Diving compass – Compass intended for diver navigation
• Diving contractor – The legal persona responsible for professional diving operations for a client
• Diving cylinder – Cylinder to supply breathing gas for divers
• Diving destination – Places where recreational divers go on vacation
• Diving Diseases Research Centre (DDRC) – British hyperbaric medical organisationPages displaying short descriptions of redirect targets
• Diving disorders – Physiological disorders resulting from underwater diving
• Diving environment – Characteristics of an environment in which underwater diving takes place
• Diving equipment – Equipment used to facilitate underwater diving
• Diving equipment maintenance and testing – Ensuring that the equipment is safe to use
• Diving equipment technician – Person who maintains, repairs and tests diving and support equipment
• Diving fatalities – Deaths associated with underwater diving
• Diving flag – Flag signal indicating divers are in the water nearby
• Diving gas analysis – Measuring the components in a breathing gas blend
• Diving glove – Hand protection worn while driving
• Diving hand signals – A form of sign system used to communicate underwater
• Diving harness – Item fastened around a diver which allows the diver to be lifted
• Diving hazards – Agents and situations that pose a threat to the underwater diver
• Diving heavy – Underwater diving while intentionally negatively buoyant
• Diving helmet – Rigid head enclosure with breathing gas supply worn for underwater diving
• Diving incident and accident investigation – Forensic investigation of underwater diving accidents
• Diving instructor – Person who trains and assesses underwater divers
• Diving Instructor – Person who trains and assesses underwater divers
• Diving jackstay – Form of guideline laid between two points to guide the diver
• Diving jargon – Definitions of jargon, diver slang and acronyms used in underwater diving
• Diving ladder – Ladder to facilitate egress from the water by divers
• Diving law – Laws directly affecting diving activities
• Diving legislation – Legislation directly affecting diving activity
• Diving light – Portable light source for use underwater
• Diving line signals – Standard signals coded in the form of tugs on the diver's lifeline
• Diving locations – Places that divers go to enjoy the underwater environment
• Diving logbook – Record of diving history of an underwater diver
• Diving mask – Watertight air-filled face cover with view-ports for improving underwater vision
• Diving Medical Advisory Council (DMAC) – Independent organisation of diving medical specialists from Northern Europe
• Diving medical examination – Assessment of medical fitness to dive
• Diving medical examiner – A medical practitioner registered to assess medical fitness to dive
• Diving Medical Examiner – A medical practitioner registered to assess medical fitness to dive
• Diving medical practitioner – Specialist in diagnosis, treatment and prevention of disorders caused by underwater diving
• Diving Medical Practitioner – Specialist in diving medicine
• Diving medical technician – Person trained in advanced first aid for divers
• Diving Medical Technician – Person trained in advanced first aid for divers
• Diving medicine – Diagnosis, treatment and prevention of disorders caused by underwater diving
• Diving mode – The conceptual methods of underwater diving
• Diving operation – Underwater dive and support activities to achieve a specific goal
• Diving operations record – Documentation recording a professional dive
• Diving physics – Aspects of physics which affect the underwater diver
• Diving physiology – Influences of the underwater environment on the physiology of human divers
• Diving platform (scuba) – Low freeboard platform on a dive boat to give divers easy access to the water
• Diving procedures – Standardised methods of doing things that are known to work effectively and acceptably safely
• Diving rebreather – Closed or semi-closed circuit scuba
• Diving reflex – The physiological responses to immersion of air-breathing vertebrates
• Diving regulations – Stipulations of the delegated legislation regarding the practice of underwater diving
• Diving regulator – Mechanism that controls the pressure of a breathing gas supply for diving
• Diving regulator malfunction – Failure modes of breathing gas control valves for underwater diving
• Diving response – The physiological responses to immersion of air-breathing vertebrates
• Diving safety – Risk management of underwater diving activities
• Diving safety equipment – Equipment used to facilitate underwater diving safety
• Diving safety harness – A harness by which the diver can safely be lifted
• Diving safety officer – Administrator of a US university's research diving safety program
• Diving school – Establishment for training and assessing underwater divers
• Diving Science and Technology (DSAT) – PADI affiliate and developer of recreational decompression planning tools
• Diving shot, also known as Shot line – Substantial weighted near-vertical line with buoy
• Diving signal – Signals made by divers for communication
• Diving skins – Suit worn to protect the skin from jellyfish stings, abrasion and sunburn
• Diving spread – The topside base for commercial diving operations
• Diving stage – A platform on which one or two divers stand which transports them vertically through the water
• Diving suit – Garment or device designed to protect a diver from the underwater environment
• Diving superintendent – A management position responsible for diving operations
• Diving supervisor – Professional diving team leader responsible for safety
• Diving support equipment – Equipment used in the support of an underwater diving operation
• Diving support vessel – Ship used as a floating base for professional diving projects
• Diving systems technician – A competent person who maintains and repairs diving life-support equipment
• Diving team – Group of people working together to enhance dive safety and achieve a task
• Diving team tools and equipment – Equipmemt shared by the members of a diving team
• Diving terminology – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Diving terms – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Diving theory – The knowledge required for safe diving
• Diving tourism – Tourism focused on recreational diving activities
• Diving tourism industry – Industry based on recreational diver travel
• Diving Unlimited International – American manufacturer of dry suits and other diving equipment
• Diving watch – Watch designed for underwater diving
• Diving weight – Ballast carried by a diver to counteract buoyancy or adjust trim
• Diving weighting system – Ballast carried to counteract buoyancy
• Doing It Right (scuba diving) (DIR) – Technical diving safety philosophy
• Donald, Kenneth William – British expert on underwater and exercise physiology.
• Downline (diving) – Rope from the surface to an underwater workplace
• Downstream scuba manifold – Component used to functionally connect scuba cylinders
• Dräger (company) – German manufacturer of breathing equipment
• Dräger DM20 oxygen rebreather system – Oxygen rebreather system for copper helmet
• Dräger DM40 mixed gas rebreather system – Nitrox rebreather system for copper helmet
• Dräger Dolphin – Semi-closed circuit recreational diving rebreather
• Dräger Modell 1915 Bubikopf helmet – Copper helmet for rebreather systems
• Dräger Ray – Semi-closed circuit diving rebreather
• Drift diving – Scuba diving where the diver is intentionally transported by the water flow
• Drill Master diving accident – Fatal diving bell accident off Norway in 1974
• Drop tank (scuba) – Scuba set placed along the guideline on a cave dive for later use
• Drowning – Respiratory impairment resulting from being in or underneath a liquid
• Dry bell – Hyperbaric chamber for transporting diversvertically through the water
• Dry Combat Submersible – Midget submarine project
• Dry suit – Watertight clothing that seals the wearer from cold and hazardous liquids
• Dry suit blowup – Over-inflation of a dry suit causing uncontrolled ascent
• Dry suit diver – Certification for diving in a dry suit
• Dry suit inflation cylinder – Diving cylinder dedicated for suit inflation gas
• Dry suit inflation hose – Low pressure inflation gas supply
• Dry suit inflation valve – Manual valve to admit low pressure gas into a diving dry suit
• DSRV-2 Avalon – Mystic-class deep-submergence rescue vehicle
• DSV-5 Nemo – Submersible used by the United States Navy
• DSV Alvin – Crewed deep-ocean research submersible
• DSV Bakunawa – Crewed full ocean depth rated submersible
• DSV Fendouzhe – Chinese deep submergence vehicle
• DSV Limiting Factor – Crewed full ocean depth rated submersible
• DSV Sea Cliff – US Navy crewed deep-ocean research submersible
• DSV Shinkai – Crewed research submersible
• DSV Shinkai 2000 – Japanese crewed research submersible
• DSV Shinkai 6500 – Japanese crewed research submersible
• DSV Turtle – US Navy crewed deep-ocean research submersible
• Dual bladder buoyancy compensator – Scuba diving buoyancy compensator with redundant air bag
• Duckbill valve – Type of check valve
• Dump valve (diving) – Pressure relief and manual vent on diving buoyancy compensator
• Dutch Underwater Sports Association – Dutch governing body for underwater sports
• Duty of care – Legal standard of care in activity
• Dwell time (filtration) – Time that fluid spends passing through active filter medium
• Dynamic apnea – Freediving disciplines where the diver swims horizontally under water
• Dynamic compression of the airways, also known as Dynamic airway compression – Mechanism reducing lung airway section area during forced expiration
• Dynamic positioning – Automatic ship station- and heading-holding systems
• Dynamically positioned vessel (DPV) – Ship with automatic station- and heading-holding systems
• Dysbaric osteonecrosis – Ischemic bone disease caused by decompression bubbles
• Dysbarism – Medical conditions resulting from changes in ambient pressure

E

• Ear clearing, also known as ear equalisation – Equalising of pressure in the middle ears
• Ebullism – Formation of vapour bubbles in bodily fluids due to reduced environmental pressure
• Ecological impact of recreational diving – Effects of scuba diving on the underwater environment
• Eelume – Autonomous underwater vehicle being developed by Eelume AS
• Effects of drugs on fitness to dive – Known side-effects and contraindications of drugs commonly used by divers
• SS Egypt#Salvage – Salvage of gold bullion from wreck using an armoured observation bell
• Ekman transport – Net transport of surface water perpendicular to wind direction
• Electro-galvanic oxygen sensor – Electrochemical device for measuring oxygen partial pressure
• Elecrtonically controlled closed circuit rebreather – Rebreather in which the partial pressure of oxygen is automatically controlled and monitored
• Emergency ascent – An ascent to the surface by a diver in an emergency
• Emergency buoyant ascent – Emergency procedure in underwater diving
• Emergency gas supply – Alternative independent breathing gas supply carried by a diver
• Emergency procedure – Plan of action to deal with an emergency
• Emergency Response Diving International (ERDI) – American organisation for training and certification of emergency response divers
• Emergency response plan – Action to be taken in specific emergencies
• Emergency swimming ascent (ESA) – Emergency procedure used by scuba divers
• Engineer diver (disambiguation)
• Engineering controls – Hazard controls that are physical changes to the workplace
• Engineering redundancy – Duplication of critical components to increase reliability of a system
• Entanglement (hazard) – Environment which may restrain the diver's freedom of movement by snagging on the diver or equipment
• Entry level diver training – Minimum standard for unsupervised recreational scuba diving
• Environmental effects of scuba diving – Effects of recreational scuba diving on the underwater environment
• Environmental impact of recreational diving – Effects of scuba diving on the underwater environment
• Environmental impact of scuba diving – Effects of recreational scuba diving on the underwater environment
• Épaulard – French remotely operated underwater vehicle of the Ifremer
• Equalising the ears – Balancing pressure in the middle ears with ambient pressure
• Equivalent air depth – Method of comparing decompression requirements for air and a given nitrox mix
• Equivalent narcotic depth – Method for comparing the narcotic effects of a mixed diving gas with air
• Ergonomics of diving equipment – Interaction between diving equipment and the diver
• Escape breathing apparatus – Self contained breathing apparatus providing gas to escape from a hazardous environment
• Escape trunk – Ambient pressure escape system for submarines
• European Diving Technology Committee (EDTC) – International organisation for improving professional diver safety
• European Scientific Diver – A diver competent to perform as a member of a scientific diving team.
• European Scientific Diving Panel – A panel of the European Network of Marine Research Institutes and Stations
• European Underwater and Baromedical Society (EUBS) – Source of information for diving and hyperbaric medicine
• European Underwater Federation (EUF) – Umbrella organisation representing scuba diver training organisations in Europe
• Evacuation plan – Removal of personnel from a high risk area or a developing incident to a safer place
• Excursion umbilical – A diver's umbilical supplied from a bell gas panel
• Exercise Paddington Diamond – Joint Bolivian-British-Swiss scuba diving expedition to Lake Titicaca
• Expanding square search – Search pattern expanding stepwise outward from datum
• Explorer AUV – Autonomous underwater vehicle from People's Republic of China
• Exponential–Linear model – Decompression model based on exponential gas uptake and linear elimination
• Explosive ordnance disposal (United States Navy) – US Navy personnel who render safe or detonate unexploded ordnance
• Exposure assessment – Measuring toxic or environment exposure
• Extended range surface-supplied air diver – Person competent to dive with surface-supplied air to 50m using a wet bell and hot-water suit

F

• Federación Española de Actividades Subacuáticas (FEDAS) – Spanish national federation for underwater activities, affiliated to CMAS
• Fédération Française d'Études et de Sports Sous-Marins (FFESSM) – French diver training and certification agency
• Federazione Italiana Attività Subacquee (FIAS) – Italian non-profit recreational diver training organisation affiliated to CMAS
• Feet fresh water – Unit of pressure equal to 1/34 atm.
• Fenzy – French manufacturer of industrial and diving breathing equipment
• Fernez, Maurice – French inventor and pioneer in underwater breathing apparatus
• Ferraro, Luigi – Officer of the Royal Italian Navy and pioneer of Italian submarine warfare
• Fibre wound composite cylinder – Pressure vessel with fiibre structural reinforcement
• Fick's laws of diffusion – Mathematical descriptions of molecular diffusion
• Fife, William Paul – US Air Force officer and hyperbaric medicine researcher
• Filling whip – High pressure hose for filling compressed gas cylinders
• Fin retainer – Rubber straps for securing swimfins to the feet
• Finning techniques – Techniques used by divers and surface swimmers using swimfins
• Finswimming – Competitive watersport using swimfins for propulsion
• Finswimming at the 2001 World Games – Competition held in Akita, Japan
• Finswimming at the 2001 World Games – Men's 50 m apnoea – Competition held in Akita, Japan
• Finswimming at the 2005 World Games – Men's 50 m apnoea – Competition held in Duisburg, Germany
• Finswimming at the 2009 Asian Indoor Games – Competition held in Mỹ Đình National Aquatics Sports Complex, Hanoi, Vietnam
• Finswimming at the 2009 World Games – International competition in Kaohsiung
• Finswimming at the 2009 World Games – Men's 50 m apnoea – Event in Kaohsiung, Taiwan
• Finswimming at the 2011 SEA Games – Watersport competition in Palembang, Indonesia
• Finswimming at the 2021 SEA Games – Competition at Mỹ Đình Aquatics Center in Hanoi, Vietnam
• Finswimming at the 2023 SEA Games – Competions held at Phnom Penh, Cambodia
• Finswimming at the World Games – Trend sport at the World Games
• Finswimming in Australia – Competitive watersport
• Finswimming in the United Kingdom – Competitive watersport
• Finswimming in the United States – Competitive watersport
• Finswimming World Championships – International event for the underwater sport of finswimming
• First aid – Emergency first response medical treatment
• Fischer, George R. – American underwater archaeologist
• Fitness to dive, also known as fitness for diving – Medical fitness of a person to function safely underwater under pressure
• Fleuss, Henry – British inventor of diving equipment
• Flicker fusion threshold – Concept in the psychophysics of vision
• Flushing the loop – Rebreather diving safety procedure
• Flying after diving – Precautions against decompression sickness when ascending to altitude after diving
• FNRS-2 – First bathyscaphe
• FNRS-3 – Bathyscaphe of the French Navy
• Force – Influence that can change motion of an object
• Formoza Military Unit – Polish Special Forces unit
• Fraction of inspired oxygen – Volumetric proportion of oxygen to other constituents in a breathing gas
• Franzén, Anders – Swedish marine technician and amateur naval archaeologist
• Free immersion apnea – Human-powered freediving discipline
• Free-flow diving helmet, also known as Free-flow helmet – Helmet which supplies a continuous flow of air to the diver
• Freediving – Underwater diving without breathing apparatus
• Freediving blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
• Freeflow – A state of continuous flow of breathing gas in an underwater breathing apparatus
• French commando frogmen – Combat swimmer unit of the French Navy
• Frenzel maneuver – Ear equalization technique originally developed for dive bomber pilots
• Fresh gas flow (disambiguation) – Gas added to the recycled gas of a rebreather or anesthetic machine
• Freshwater diving – Underwater diving in fresh water
• Frog kick – Finning propulsion kick used particularly by cave and wreck divers
• Frogman – Tactical scuba diver
• Frogman Corps (Denmark) – Danish maritime special operations unit
• FROGS (Full Range Oxygen Gas System) – Closed circuit oxygen diving rebreather
• Fuerzas Especiales – is a special forces unit of the Mexican NavyPages displaying wikidata descriptions as a fallback
• Fukuryu – Japanese divers intended to manually detonate mines on invading ships
• Full-face diving mask – Diving mask that covers the mouth as well as the eyes and nose
• Full facepiece – User respiratory inteface with breathing apparatus that covers the nose, mouth and eyes
• Full-face snorkel mask – Breathing apparatus for surface swimming

G

• Gaiters (diving) – Accessories used to restrict volume of a dry suit over the lower legs
• Gas blender – Person who blends breathing gas mixtures for scuba diving and fills diving cylinders
• Gas blending – Producing special gas mixtures to specification
• Gas blending for scuba diving – Mixing and filling cylinders with breathing gases for use when scuba diving
• Gas booster – Machine to increase the pressure of compressed gas
• Gas endurance – The time a gas supply will last
• Gas exchange – Process by which gases diffuse through a biological membrane
• Gas extender – Type of semi-closed circuit diving rebreather
• Gas-integrated dive computer – A dive computer that displays the pressure of breathing gas remaining in the cylinder
• Gas laws – Scientific description of the behaviour of gases as physical conditions vary
• Gas man – Person who controls the breathing gas supply to a surface-supplied mixed-gas diver
• Gas matching – Ensuring that reserve breathing gas is sufficient to supply the dive buddy
• Gas panel – Breathing gas distribution panel for surface-supplied diving
• Gas-reclaim system – Equipment to recover exhaled gas from a diver to tecover the helium content
• Gas storage bank – Group of similar size high pressure cylinders mounted together and connected to a common manifold
• Gas storage quad – Group of similar size high pressure cylinders
• Gas storage tube – Large volume, high pressure gas storage cylinder
• Gas switch – Changing the breathing gas mixture during a dive
• Gas switching – Changing the breathing gas mixture during a dive
• Gas toxicity – Degree of harmfulness of gases
• Gay-Lussac's law – Relationship between pressure and temperature of a gas at constant volume
• German commando frogmen – German postwar commando amphibious warfare force
• Global Explorer ROV – Deep water science and survey remotely operated vehicle
• Global Underwater Explorers (GUE) – Recreational/technical scuba training and certification agency
• Glossary of breathing apparatus terminology – Definitions of technical terms used in connection with breathing apparatus
• Glossary of underwater diving terminology, also known as Glossary of underwater diving terms or Glossary of SCUBA diving – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Glossary of underwater diving terminology: A–C – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Glossary of underwater diving terminology: D–G – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Glossary of underwater diving terminology: H–O – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Glossary of underwater diving terminology: P–S – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Glossary of underwater diving terminology: T–Z – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Goldfinder – Autobiography of British diver and treasure hunter Keith Jessop
• Gold Rush: White Water – American television series
• Goldfish-class ROUV – Light class of Chinese remotely operated underwater vehicle
• Goodman handle – Mounting which holds a dive light on the back of the diver's hand
• Gradient factor – Method for adjusting conservatism of decompression algorithms
• Gradient factor in decompression modelling – A way for users to adjust the conservatism of a decompression algorithm in software
• Green Fins – Organisation in South East Asia for preservation of coral reefs by improving diver behavior
• GROM Military Unit – Polish special forces unit
• GRUMEC, also known as Brazilian commando frogmen – Brazilian Navy special forces diving unit
• Guide line – Line deployed by scuba divers for navigation
• Gyrojet – Firearm that fires small rocket projectiles

H

• Haenyeo – Female divers of Jeju, South Korea
• Halcyon PVR-BASC – Semi-closed circuit depth compensated passive addition diving rebreather
• Halcyon RB80 – Non-depth-compensated passive addition semi-closed circuit rebreather
• Haldane, John Scott – British physiologist and decompression researcher (1860–1936)
• Haldane's decompression model – Decompression model developed by John Scott Haldane
• Half + 15 bar – Rule of thumb for scuba gas management
• Half mask – Diving mask covering the nose and eyes
• Half time (physics) – The time taken for a quantity to decrease by half in an exponential decay process
• Halocline – Stratification of a body of water due to salinity differences
• Hamilton, Robert William Jr. – American physiologist and researcher in hyperbaric physiology.
• Hand-off a cylinder – Transfer a scuba cylinder from one diver to another in the water
• Hand-off cylinder – Scuba set that can be passed to another diver
• Hans Hass Award – Award in recognition of contribution made to the advancement of our knowledge of the ocean
• Hans Hass – Austrian biologist, film-maker, and underwater diving pioneer
• Hawaiian sling – Simple form of underwater speargun
• Hazard – Situation or object that can cause damage
• Hazard analysis (HAZID) – The identification of present hazards as the first step in a process to assess risk
• Hazard elimination – Hazard control by removing the hazard
• Hazard substitution – Replacing a material or process with a lower risk alternative
• Hazardous Materials Identification System – Numerical hazard rating using colour coded labels
• Hazards of the aquatic environment – Hazards inherent to being underwater
• Hazards of the specific diving environment – Factors which vary between diving environments
• Hazmat diver – Professional diver working in hazardous materials environments
• Hazmat diving – Underwater diving in a known hazardous materials environment
• Hazmat diving decontamination – Removing hazardous environmental contaminants from the diver after a dive
• H-BRUV – Horizontally aligned baited remote underwater video
• Health and Safety Executive (HSE) – United Kingdom government agency
• Healthways (scuba gear company) – Defunct firm which made scuba gear
• Heckler & Koch P11 – Five-barreled underwater rocket dart pistol
• Heinke (diving equipment manufacturer) – British manufacturer of diving equipment
• HeinrichsWeikamp – German manufacturer of dive computers and other underwater electronics for recreational diving.
• Helgoland Habitat – Ambient pressure underwater habitat
• Heliair – Breathing gas mixed from air and helium
• Helicopter Aircrew Breathing Device, also known as helicopter escape set – Small scuba device for escape from ditched helicopters
• Helicopter turn – Rotation about a vertical axis by an underwater diver using only fins
• Heliox – A breathing gas mixed from helium and oxygen
• Helium analyzer, also known as Helium analyser – Instrument to measure the concentration of helium in a gas mixture
• Helium reclaim system – System for recovering exhaled breathing gas
• Helium release valve – Feature on some watches for saturation diving
• Helium speech unscrambler – Technology for reducing hyperbaric speech distortion
• Helix Energy Solutions Group – Provider of offshore services and ROV operations
• Helmet squeeze – Type of injury caused by a pressure difference between the inside and outside of a diving helmet
• Helmet weight – Ballast added to a diving helmet to prevent it from floating
• Hempleman, Henry Valence – British decompression researcher
• Henry's law – Gas law regarding proportionality of dissolved gas
• Hierarchy of hazard controls – System used in industry to eliminate or minimize exposure to hazards
• High pressure breathing air compressor – Machine to provide atmospheric air at high pressure for breathing
• High pressure storage cylinder – Container for storing gases at high pressure
• High-pressure nervous syndrome – Reversible disorder caused by breathing helium based gas below about 150 m
• High-pressure water jetting – The use of very high pressure water for removing contamination and coatings from hard surfaces
• Hill, Leonard Erskine – British physiologist and diving physiology researcher
• Hills, Brian Andrew – Physiologist who worked on decompression theory
• History of decompression research and development – Chronological list of notable events in the history of diving decompression.
• History of Diving Museum – Museum of underwater diving in Islamorada, Florida
• History of scuba diving – History of diving using self-contained underwater breathing apparatus
• History of underwater diving
• Hoppe-Seyler, Felix – German physiologist and chemist (1825–1895)
• Hogarthian scuba configuration – Scuba harness arrangement developed by Bill Main
• Hoke valve – Gas recirculation control valve on MK V helium hemet
• Hookah (diving) – Surface-supplied diving equipment without the communication, lifeline and pneumofathometer hose
• Hookah diving – Underwater diving using a basic air hose from the surface
• Hot water suit – A wetsuit with a supply of heated water to keep a diver warm
• Hot water system (diving) – Water heating and supply system for hot-water diving suits
• Huggins, Karl E. – American decompression researcher
• Human factors in diving equipment design – Influence of the interaction between the user and the equipment on design
• Human factors in diving safety – The influence of physical, cognitive and behavioral characteristics of divers on safety
• Human physiology of underwater diving, also known as Human physiology of diving – Influences of the underwater environment on the physiology of human divers
• Human torpedo – Early form of diver propulsion vehicle
• Hydreliox – Breathing gas mixture of hydrogen, helium, and oxygen
• Hydrocleaning – Use of a water jet for cleaning hard surfaces
• Hydrogen narcosis – Psychotropic state induced by breathing hydrogen at high partial pressures
• Hydrogen sulfide – Poisonous, corrosive and flammable gas
• Hydrophobe – Molecule or surface that has no attraction to water
• Hydrostatic pressure – The static pressure exerted by the weight of the fluid column above the point
• Hydrostatic test – Non-destructive test of pressure vessels
• Hydrox (breathing gas) – Breathing gas mixture experimentally used for very deep diving
• Hyperbaric evacuation and rescue – Emergency transport of divers under a decompression obligation to a place of safety
• Hyperbaric evacuation facilities – Systems to evacuate saturation divers in an emergency
• Hyperbaric evacuation system – Equipment for emergency transport of divers under a decompression obligation to a place of safety
• Hyperbaric evacuation unit – Pressure vessel in which divers are transported under pressure in an emergency
• Hyperbaric lifeboat – Lifeboat for transporting people under pressure
• Hyperbaric medicine – Medical treatment at raised ambient pressure
• Hyperbaric nursing – Nursing specialty involved with hyperbaric oxygen therapy
• Hyperbaric oxygen treatment – Medical oxygen treatment at raised pressure
• Hyperbaric oxygen treatment table – Planned hyperbaric exposure using oxygen breathing gas as medical treatment
• Hyperbaric reception facility – Saturation facility on standby in case evacuation is necessary
• Hyperbaric rescue vessel – Ship to recover hyperbaric evacuation units
• Hyperbaric speech distortion – Speech distortion at high ambient pressure
• Hyperbaric stretcher – Portable pressure vessel to transport a person under pressure.
• Hyperbaric treatment – Medical treatment at raised ambient pressure
• Hyperbaric treatment schedules – Planned hyperbaric exposure using a specified breathing gas as medical treatment
• Hyperbaric treatment tables – Planned hyperbaric exposure using a specified breathing gas as medical treatment
• Hyperbaric welding – Welding metal at elevated pressure
• Hypercapnia – Abnormally high tissue carbon dioxide levels
• Hyperoxia – Exposure of tissues to abnormally high concentrations of oxygen.
• Hyperthermia – Elevated body temperature due to failed thermoregulation
• Hyperventilation – Excessive breathing
• Hyperventilation-induced blackout – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
• Hypobaric decompression – Reduction in pressure to lower than normal sea level atmospheric pressure
• Hypocapnia – State of reduced carbon dioxide in the blood
• Hypothermia – Human body core temperature below 35.0 °C (95.0 °F)
• Hypoventilation – Insufficient breathing
• Hypoxia (medicine) – Medical condition of lack of oxygen in the tissues
• Hypoxia of ascent – Loss of cosciousness during ascent from a breathhold dive
• Hypoxic blackout – Loss of consciousness due to cerebral hypoxia
• Hypoxic trimix diver – Recreational technical diving certification level

I

• Ice diving – Underwater diving under ice
• Ichthyander Project – Soviet underwater habitat project of the 1960s
• Ictineu 3 – Crewed submersible
• IDA71 – Russian military rebreather for underwater and high altitude use
• Ideal gas law – Equation of the state of a hypothetical ideal gas
• IDRCF – International Diving Regulators and Certifiers Forum
• IMCA Code of Practice for Offshore Diving – Guidance document for member organisations
• Immersion finswimming – Underwater swimming using mask, monofin and underwater breathing apparatus in a swimming pool
• Immersion pulmonary oedema – Body fluid accumulated in the lungs due to immersion in a liquid
• Immersion response – The physiological responses to immersion of air-breathing vertebrates
• Independent doubles – Two fully redundant back-mounted scuba sets with no cross-connection
• Independent twin cylinders – Two diving cylinders mounted together but not connected for gas flow
• In-water cleaning – Methods of removing contaminants from underwater surfaces
• In-water recompression – In-water treatment for decompression sickness
• In-water surface cleaning – Methods of removing contaminants from underwater surfaces
• Incident pit – Conceptual model for explaining incident development and recovery
• Index of recreational dive sites – Alphabetical listing of articles on porular places for recreational diving
• Index of underwater divers – Alphabetical listing of articles about underwater divers
• Index of underwater diving – Alphabetical listing of underwater diving related topics
• Inert gas counterdiffusion – Diffusion of one inert gas into body tissues while another inert gas is diffusing out
• Inherent unsaturation – Physiological effect of oxygen metabolism on total dissolved gas concentration in venous blood
• Inland diving – Diving in waters inland of the coastal high water mark.
• Inner ear barotrauma – Pressure injury to the inner ear
• Inner ear decompression sickness – Medical condition caused by inert gas bubbles forming out of solution
• Inshore diving – Diving in coastal territorial waters
• Instinctive drowning response – Instinctive reaction that occurs in humans when close to drowning
• Insulán, Stig – Inventor of an adjustable automatic exhaust valve for variable volume dry suits
• Integrated Diver Display Mask – Diving half-mask with integrated head-up instrument display
• Integrated weight system – Diver weights carried on the buoyancy compensator or safety harness
• Integrated weights – Diving weights carried in pockets on the buoyancy compensator
• Intelligent Water class AUV – Autonomous underwater vehicle for the People's Liberation Army Navy
• International Association for Handicapped Divers (IAHD) – Non-profit organisation based in the Netherlands
• International Association of Nitrox and Technical Divers (IANTD) – Recreational and technical scuba training and certification agency
• International Bluewater Spearfishing Records Committee – Committee of special interest
• International Coral Reef Society – Non-profit scientific society for the conservation of coral reefs.
• International Divers Alert Network – Independently administered nonprofit DAN regional organizations
• International Diving Institute – American commercial diver training school
• International Diving Regulators and Certifiers Forum (IDRCF), also known as International Diving Regulators Forum – International forum of professional diver accreditation organisations
• International Diving Schools Association (IDSA) – Organisation to develop common standards for commercial diver training
• International Life Saving Federation – Umbrella organization of the national lifesaving organizations
• International Marine Contractors Association (IMCA) – International trade association for the marine contracting industry
• International Organization for Standardization (ISO) – International standards development organization
• International Scuba Diving Hall of Fame – Annual event recognizing recreational scuba industry contributors
• International Submarine Escape and Rescue Liaison Office – Organization that coordinates international submarine search and rescue operations.
• International Underwater Cave Rescue and Recovery – Cave diving rescue/recovery organization
• Interspiro DCSC – Military semi-closed circuit passive addition diving rebreather
• Intervention AUV – Type of autonomous underwater vehicle capable of autonomous interventions
• Intestinal squeeze – Injury to intestines by expanding gas during decompression
• Introductory diving – Non-certification scuba diving experience
• Introductory scuba experience – Non-certification scuba diving experience
• Investigation of diving accidents – Forensic investigation of underwater diving accidents
• In-water recompression – In-water treatment for decompression sickness
• iRobot Seaglider – Deep diving autonomous underwater vehicle for long term missionsPages displaying short descriptions of redirect targets
• iSimangaliso Marine Protected Area – Marine conservation area in northern kwaZulu-Natal in South Africa
• Isobaric counterdiffusion – Gaseous diffusion through body tissue at constant pressure
• Isolation manifold – Upstream scuba manifold with a shut-off valve
• Isolation-manifolded twin cylinders – Scuba set with two back-mounted cylinders connected by a manifold with an isolation valve
• Israeli Diving Federation (TIDF) – Israeli recreational diver training and certification agency
• Italian auxiliary ship Olterra – Undercover Italian auxiliary ship from World War II

J

• Jacket harness – Type of surface-supplied diving safety harness
• Jackstay – Substantial line between two points used to guide or support.
• Jackstay (diving) – Substantial underwater guide line
• Jackstay search – Underwater search along a laid down line
• Jagdkommando – Austrian Armed Forces' Special Operations group
• JAGO (German research submersible) – Manned German research submersible
• Jersey upline – A buoyed line serving as a position control during decompression
• JIM suit – Type of atmospheric diving suit.
• Job safety analysis (JSA) – Procedure to integrate safety practices into a particular task
• Johnson Sea Link accident – Manned submersible incident in which two divers died
• Jonline – A short line used by scuba divers to clip themselves to something
• Jump jacket – Surface-supplied diving safety harness with buoyancy compensation
• Jump spool – Diving navigation and safety equipment

K

• Kaikō ROV – Japanese remotely operated underwater vehicle for deep sea exploration
• Kaşif ROUV – Turkish remotely operated underwater vehicle
• Klingert, Karl Heinrich – German mechanic and inventor of an early surface-supplied diving suit.
• Karst Underwater Research – Non-profit organization that specializes in the research and documentation of karst aquifers
• Kayak diving – Recreational diving from a canoe or kayak
• Keel weight (diving) – Weight added to a diver's backplate
• Kilsby sinkhole – Sinkhole in Mount Gambier, Southern Australia.
• Kimiuo Aisek Memorial Museum – Museum in Chuuk State, Federated States of Micronesia
• KISS (rebreather) – Manual closed circuit mixed gas rebreather
• Kommando Spezialkräfte Marine – German postwar commando amphibious warfare force
• Kongsberg Mesotech – Manufacturer of sonar equipment for underwater imaging and detection
• Konsul-class submersible – Russian Navy deep sea submergence vehicle
• KOPASKA – Indonesian Navy special operations and demolition unit
• Kreeft, Peter – 18th Century German inventor and diver
• Kronan (ship) – Swedish Navy ship of the 1670s
• Kursk submarine disaster salvage operation – Raising the wreck of a Russian nuclear submarine

L

• Lambertsen Amphibious Respiratory Unit (LARU) – Early closed circuit oxygen diving rebreather
• Lambertsen, Christian J. – American environmental and diving medicine specialist
• LAR-5 – Military oxygen tebreather by Drägerwerk
• LAR-6 represented by Drägerwerk – German manufacturer of breathing equipment
• LAR-V represented by Drägerwerk – German manufacturer of breathing equipment
• Laryngospasm – Involuntary contraction of the vocal folds restricting inhalation
• The Last Dive – Non-fiction book by Bernie Chowdhury about a double wreck diving fatality
• Latent hypoxia – Lung gas and blood oxygen concentration sufficient to support consciousness only at depth
• Launch and recovery system (diving) – Equipment used to deploy and recover a diving bell, stage, or ROV
• Lazy shot – A diving shotline which does not reach the bottom
• Legal aspects of underwater diving – How diving activities are affected by law
• Le Prieur, Yves – French naval officer and inventor of a free-flow scuba system
• Life support supervisor – Senior life support technician
• Life support technician – A member of a saturation diving team who operates the surface habitat
• Life-support equipment – Equipment which is necessary to support life in a hostile environment
• Life-support system – Technology that allows survival in hostile environments
• Lifeline (diving) – A rope connecting the diver to an attendant, usually at the surface
• Lifting bag – Airtight bag used for underwater buoyant lifting when filled with air
• Lightweight demand diving helmet, also known as Lightweight demand helmet – Underwater breathing apparatus
• Lightweight diving helmet – Diving helmet supported by the head and neck
• Limpet mine – A type of naval mine which is attached to a target by magnets
• Line arrow – Marker used on cave guide lines to provide safety information to divers
• Line holder – Simple device for storing and deploying line underwater
• Line marker – Marker used on cave guide lines to provide safety information to divers
• Lipid – Substance of biological origin that is soluble in nonpolar solvents
• Liquid breathing – Respiration of oxygen-rich liquid by a normally air-breathing organism
• List of British records in finswimming
• List of Commonwealth records in finswimming
• List of DAN publications – List of Divers Alert Network publications
• List of designations under the Protection of Wrecks Act – All sites designated under the UK Protection of Wrecks Act
• List of diver certification organisations – Agencies which issue certification for competence in diving skills
• List of diver certification organizations – Agencies which issue certification for competence in diving skills
• List of Divers Alert Network publications
• List of diving environments by hazard – Example types of a class of diving hazard
• List of diving environments by type – Variety of environments that people may dive in
• List of diving hazards and precautions – Hazards associated with underwater diving
• List of European records in finswimming
• List of legislation regulating underwater diving – List of national and state legislation regulating underwater diving
• List of military diving units
• List of notable scuba divers – Hierarchical outline list of biographical articles about underwater divers
• List of researchers in diving physiology and medicine
• List of researchers in underwater diving
• List of scuba divers – Hierarchical outline list of biographical articles about underwater divers
• List of shipwrecks in international waters
• List of shipwrecks of Africa
• List of shipwrecks of Asia
• List of shipwrecks of Europe
• List of shipwrecks of Hong Kong
• List of shipwrecks of North America
• List of shipwrecks of Oceania
• List of shipwrecks of South America
• List of shipwrecks of the Isles of Scilly
• List of shipwrecks of the Isles of Scilly (19th century)
• List of signs and symptoms of diving disorders – Evidence of physiological disorders resulting from underwater diving
• List of types of diving environments – Variety of environments that people may dive in
• List of undersea explorers
• List of underwater divers – List of underwater divers whose exploits have made them notable.
• List of underwater diving hazards and precautions – Hazards associated with underwater diving
• List of underwater explorers
• List of United States Navy SEALs – Notable members of the US Navy SEALs and UDTs
• List of United States records in finswimming
• List of world records in finswimming
• List of wreck diving sites – List of shipwreck sites which are popular amongst scuba divers for wreck diving.
• Lists of shipwrecks – Index to Wikipedia's lists of shipwrecks
• Little Blue Lake – Flooded sinkhole dive site in South Australia
• Live-aboard dive boat – Boat providing accomodations and diving platform for multi-day trips
• Live-boat diving – Diving from a boat which is under way (not moored)
• Live-boating – Diving from a vessel under way
• Liveaboard – Way of using a boat
• Lobster hook – Implement for extracting lobsters from holes
• Lockout–tagout (LOTO) – Safe isolation of dangerous equipment during maintenance or testing
• London Diving Chamber Dive Lectures – Series of public lectures that have been hosted at the Royal Geographical Society in London
• Long distance part of the 2011 Finswimming World Championships – International competition in Hódmezővásárhely, Hungary
• Long term health effects of diving – Effects of frequent underwater diving on health
• Long-Term Mine Reconnaissance System – American torpedo tube-launched underwater search and survey unmanned undersea vehicle
• Longshore current – A current parallel to the shoreline caused by waves approaching at an angle to the shoreline
• Longshore drift – Sediment moved by the longshore current
• Loop rebreather – Rebreather architecture with one-way flow
• Louis de Corlieu – French naval officer and inventor of the swimfin
• Low Impact Diver – PADI specialty to improve poor buoyancy, trim and finning skills in recreational divers
• Low impact diving – Scuba diving that has minimal environmental effect
• Low pressure breathing air compressor – Machine to provide atmospheric air at low pressure for breathing
• LR5 – Crewed submersible for submarine rescue
• LR7 – Manned submersible undersea rescue vehicle
• Lung over-pressure injury – Damage to lungs caused by internal overpressure
• Lung overexpansion injury – Injury to the lungs caused by excessive internal pressure
• Lung overpressure injury – Injury to the lungs caused by excessive internal pressure
• Lunocet – Biomimetic monofin
• Lyons Maritime Museum – Diving history museum in St. Augustine, Florida

M

• Magnesium torch – Bright light source made from magnesium, which burns underwater
• Man in the Sea Museum – Diving history museum in Panama City Beach, Florida
• Management of multiple cylinders – Techniques for carrying and using multiple scuba sets
• Manifold (scuba) – Component to functionally connect scuba cylinders
• Manifolded twin scuba set, also known as Manifolded twin set or manifolded twins – Two scuba cylinders functionally connected by a manifold
• Manually controlled closed circuit rebreather – Rebreather in which the oxygen content of the loop gas is controlled by the diver
• MARCOS – Indian Navy special operations force
• Mares (scuba equipment) – Italian manufacturer of underwater diving equipment.
• Marine Commandos – Marine special operations group of the Lebanese Army
• Marinejegerkommandoen – Norwegian naval special operations unit
• Maritime archaeology – Archaeological study of human interaction with the sea
• Maritime Archaeology Sea Trust – Charitable trust in the UK
• Maritime Archaeology Trust – Charitable organization in Great Britain
• Mark IV Amphibian – British military oxygen rebreather
• Mary Rose – Carrack-type warship of the English Tudor navy
• Mass fraction blending – Mixing gas by measuring added mass of each component
• Master diver (United States Navy) – Senior diver rating in US Navy
• Master Instructor – Grade of recreational dive instructor with some experience
• Master Scuba Diver – The highest non-leadership recreational scuba diver certification issued by some agencies
• Maximum operating depth – Depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable limit
• Maximum voluntary ventilation – Limit of amount than can be breathed in a minute
• Maya AUV India – Autonomous underwater vehicle from National Institute of Oceanography, India
• McCann Rescue Chamber – Device for rescuing submariners
• Mechanical dead space – Space in breathing apparatus in which the breathing gas must flow in both directions
• Mechanism of diving regulators, also known as Mechanism of the diving regulator – Arrangement and function of the components of regulators for underwater diving
• Media diver – Professional diver working in the media sector
• Media diving – Underwater diving in support of the media industries
• Medical fitness to dive – The medical fitness of a person to function safely underwater under pressure
• Medical oxygen – Oxygen used for therapeutic purposes
• Medically fit to dive – State of a person who has no medical constraints preventing them from underwater diving
• Membrane gas separation – Technology for splitting specific gases out of mixtures
• Messenger line – Light line used to pull heavier cable or lower a package along a downline
• Metabolism – Set of chemical reactions in organisms
• Metre sea water, also known as metre seawater – Unit of pressure equal to one tenth of a bar
• Middle ear barotrauma – Pressure injury to the middle ear
• Midwater, also known as Mid-water – In the water column between surface and bottom
• Military diver training – Training of underwater divers for service in the armed forces
• Military diving – Underwater diving in a military context by members of an armed force
• Mine escape set – Portable breathing apparatus intended for escape from compromised mines
• Minedykkerkommandoen – Norwegian Navy clearance diver unit
• Minentaucher – Mine clearance divers of the German Navy
• Mini Rover ROV – Small, low cost observation class remotely operated underwater vehicle
• Mir (submersible) – Self-propelled deep submergence vehicle
• Missed decompression – Unsafe adcent from dive
• Mission 31 – An undersea expedition organized by Fabien Cousteau
• Mitchell, Simon – New Zealand physician and author on diving medicine
• Mitigation – Reduction of something harmful or the reduction of its harmful effects
• Mixed gas rebreather – Rebreather using gas other than only oxygen
• Mk 1 Underwater Defense Gun – Underwater firearm developed by the United States during the Cold War
• Mk V Mod 1 Heliox helmet – US Navy standard diving helmet modified for heliox
• Mode of diving – The conceptual methods of underwater diving
• Modulated ultrasound – Technology for transmitting signals through water
• Moir, Ernest William – British civil engineer credited with inventing the first medical airlock
• Molecular diffusion – Thermal motion of liquid or gas particles at temperatures above absolute zero
• Momsen, Charles – US Navy admiral, submarine rescue (1896–1967)
• Monkey diving – Sidemount diving with a single cylinder
• Monofin – Single blade swimfin attached to both feet
• Moon pool – Opening in the base of a hull, platform, or chamber giving access to the water below
• Morse Diving – American manufacturer of diving equipment
• Morse Engineering Mk 12 helmet – US Navy deep water free-flow helmet
• Motion sickness – Nausea caused by motion or perceived motion
• Motorised Submersible Canoe – WWII British frogman delivery vehicle
• Mouth-to-mouth resuscitation – Artificial ventilation using exhaled air from the rescuer
• Mouthpiece (breathing apparatus) – Respiratory user interface
• MSDS Marine – British marine and coastal archaeological contractor
• MSM-1 – Italian deep-submergence rescue vehicle
• Msw – Metre of sea water, a unit of pressure
• Muck diving – Recreational diving on a loose sedimentary bottom
• Multi-level dive – Scuba diving in consecutively shallower depth ranges on one dive
• Muscle-memory – Consolidating a motor task into memory through repetition
• Mushroom valve – Arrangement and function of the components of regulators for underwater diving
• M-value (decompression) – Maximum inert gas supersaturation allowed for a tissue in decompression theory}

N

• Namibian Marine Corps – Combat body created in 2016
• National Academy of Scuba Educators (NASE) – Recreational scuba training and certification agency
• National Association for Cave Diving (NACD) – American non-profit organization for improving cave diving safety
• National Association of Underwater Instructors (NAUI) – Non-profit training and certification agency association of scuba instructors
• National Board of Diving and Hyperbaric Medical Technology – Non-profit organization for education and certification in diving and hyperbaric medicine
• National Diving and Activity Centre – Flooded quarry in Gloucestershire used as a recreational dive site.
• National Navy UDT-SEAL Museum – Museum of US Navy UDTs and SEALs
• National Oceanic and Atmospheric Administration (NOAA) – United States government scientific agency
• National Speleological Society Cave diving section – Organization for exploration, conservation, and study of caves in the United States
• NATO Submarine Rescue System – Project to develop an international submarine rescue system
• Nautical Archaeology Program – Graduate degree program at Texas A&M University
• Nautical Archaeology Society (NAS) – British organisation to further research in nautical archaeology for the public benefit
• Nautile – Crewed submersible owned by Ifremer
• Naval Air Command Sub Aqua Club – British organization within the Royal Navy
• Naval diving – Diving in navy applications
• Naval Diving Unit (Singapore) – Maritime special forces unit
• Naval Service Diving Section – Diving unit of the Irish Naval Service
• Naval Special Operations Command – Military unit of the Philippines Navy
• Naval Special Warfare Command (Thailand) – Special operations force within the Military of Thailand
• Naval Submarine Medical Research Laboratory – U.S. Navy research unit for submarine and diving medicine
• Navy diver (disambiguation) – Member of a country's naval forces, specializing in underwater diving
• Navy diver (United States Navy) – US Navy personnel qualified in underwater diving and salvage
• Neck dam – Flexible seal between a diving helmet and the diver's neck
• Necker Nymph – DeepFlight Merlin class positively-buoyant open-cockpit 3-seater wet sub
• Nederlandse Onderwatersport Bond (NOB) – Dutch governing body for underwater sports
• Negative buoyancy entry – Scuba diving water entry where the diver will immediately sink
• Negative pressure breathing – Breathing gas which is at a slightly lower pressure than in the resting lung
• Nemo 33 – Indoor recreational diving facility
• Nemrod – Spanish manufacturer of scuba and spearfishing equipment
• Neptune Finswimming Club – Club in Bristol, UK.
• Nereus (underwater vehicle) – Hybrid remotely operated or autonomous underwater vehicle
• Neutral buoyancy – Equilibrium between buoyancy and weight of an immersed object
• Neutral Buoyancy Laboratory – NASA astronaut training facility in Houston, Texas
• Neutral buoyancy pool – Pool of water in which neutral buoyancy is used to train astronauts
• Newtsuit – Atmospheric diving suit designed by Phil Nuytten
• New World Publications – Recreational dive guide publisher
• Night diver – Certification of competence to scuba dive at night
• Night diving – Underwater diving during the hours of darkness
• Nikonos – Brand of 35mm film amphibious cameras
• Nitrogen narcosis – Reversible narcotic effects of respiratory nitrogen at elevated partial pressures
• Nitrous oxide (medication) – Gas used as anesthetic and for pain relief
• Nitrox – Breathing gas, mixture of nitrogen and oxygen
• Nitrox blender – Person competent to blend nitrox for scuba diving
• Nitrox diver – Recreational diving qualification to dive using oxygen enriched air
• Nitrox production – Methods of producing nitrox mixtures
• NOAA Diving Manual – Training and operations manual for scientific diving
• abbreviation NDL – Maximum exposure without incurring decompression obligation
• NOGI Awards – Annual awards by Academy of Underwater Arts and Sciences.
• No-limits apnea – Freediving discipline in which the diver descends and ascends using their method of choice
• Nondestructive testing – Evaluating the properties of a material, component, or system without causing damage
• Non-freezing cold injury – Tissue injury due to sustained low temperature without freezing
• Nordic Deep – Freediving competition in Lysekil, Sweden
• Normocapnia – Normal arterial carbon dioxide levels
• Normoxic trimix diver – Recreational technical diving certification level
• Northern Ireland Federation of Sub-Aqua Clubs – National governing body for recreational diving and underwater sport in Northern Ireland
• Norwegian Diver School – Part of the Western Norway University of Applied Sciences
• No-stop limit – Diving bottom time beyond which obligatory decompression stops are incurred
• Nuclear diving – Diving in an environment where there is a risk of exposure to radioactive materials

O

• Observation bell – Closed diving bell used as an observation platform
• Occupational diver – Person who dives underwater as part of their occupation
• Occupational diver training – Training of people employed as underwater divers
• Occupational diving – Underwater diving which is part of the job
• Occupational exposure limit – Upper limit on the acceptable concentration of a hazardous substance
• Occupational hazard – Hazard experienced in the workplace
• Occupational Health and Safety Act, 1993 – South African statutory law administered by the Department of Labour
• Occupational hygiene – Management of workplace health hazards
• Occupational safety and health, also known as Occupational health and safety – Field concerned with the safety, health and welfare of people at work
• Ocean current – Directional mass flow of oceanic water generated by external or internal forces
• Ocean Guardian (Shark Shield) – Personal electromagnetic field shark deterrent device
• Ocean stratification – Layering of ocean water due to density differences
• Oceanic Worldwide – American recreational scuba equipment manufacturer
• Octopus demand valve – Secondary demand valve on a scuba regulator
• Octopus regulator – Secondary demand valve on a scuba regulator
• Offshore commercial diving – Professional diving in support of the oil and gas industry
• Offshore diving – Diving outside the territorial waters of a country
• Offshore survey – Discipline of hydrographic survey largely concerned with the oil industry
• Omitted decompression – Missed obligatory decompression stops
• Omitted decompression procedure – Procedure to reduce risk of developing decompression sickness
• Open circuit breathing apparatus – Breathing apparatus where the exhaled gas is lost to the environment
• Open circuit demand helmet – Diving helmet which provides gas on inhalation and exhausts to the surroundings
• Open ocean diving – Diving in deep water out of sight of land
• Open water (diving) – Unrestricted water with direct vertical access to the surface in contact with the atmosphere
• Open Water Diver – Entry-level autonomous diver certification for recreational scuba diving
• Open-water diving – Diving in unrestricted water when the diver has unresricted vertical access to the surface
• OpenROV – Open-source remotely operated underwater vehicle
• Operation Algeciras – Argentine plan to sabotage a British warship in Gibraltar
• Operation Source – Second World War Royal Navy midget submarine attacks on heavy German warships in Norway
• Operation Thunderhead – American amphibious mission during the Vietnam War
• Operational Diving Division (SA Navy) – Diving component of the South African Navy's Maritime Reaction Squadron
• Operations manual – Authoritative document of how things should be done in an organisation
• Oral-nasal mask – Breathing mask that covers the mouth and the nose only.
• Orca Edge – First commercially viable personal decompression computer
• Orinasal mask – Breathing mask that covers the mouth and the nose only.
• Osprey Reef – Submerged atoll in the Coral Sea, northeast of Queensland, Australia
• Outline of recreational dive sites – Hierarchical outline list of articles about rereational dive sites
• Outline of underwater divers – Hierarchical outline list of biographical articles about underwater divers
• Outline of underwater diving – Hierarchical outline list of articles related to underwater diving
• Overfall – Dangerous seas due to opposing currents and wind or strong currents over a shallow rocky bottom.
• Overconfidence effect – Personal cognitive bias
• Overhead (diving) – A physical or physiological constraint to an immediate direct vertical ascent to the surface
• Overhead environment – Environment with a physical constraint to a direct vertical ascent to the surface
• Over-learning, also known as Overlearning – Practicing newly acquired skills beyond the point of initial mastery
• Overpressure valve (rebreather loop) – Pressure relief valve on a breathing loop
• Oxygen analyser – Instrument to measure partial pressure of oxygen in a gas mixture
• Oxygen cleaning – Removal of contaminants that might cause a fire hazard in a n oxygen rich environment
• Oxygen compatibility – Usability in high-oxygen environments
• Oxygen enriched air – Air with added oxygen
• Oxygen fraction – The molar or volumetric fraction of oxygen in a gas
• Oxygen prebreathing – Procedure to reduce risk of decompression sickness before hypobaric exposure
• Oxygen service – Use in contact with high partial pressures of oxygen
• Oxygen therapy – Use of oxygen as a medical treatment
• Oxygen toxicity – Toxic effects of breathing oxygen at high partial pressures
• Oxygen window – Physiological effect of oxygen metabolism on the total dissolved gas concentration in venous blood
• Oxygen window in technical diving – Physiological effect of metabolism on total dissolved gas load in venous blood

P

• P2 – Svenskt Vrakskydd – Organization for presrvation of shipwrecks in Swedish waters
• PADI AWARE – Marine conservation non-profit organization for recreational divers
• PADI Delayed Surface Marker Buoy Diver – Diver trained to deploy a decompression buoy from depth
• PADI Discover Scuba Diving – Introductory scuba experience without certification
• PADI Low Impact Diver – Training to mitigate low entry level competence standards
• PADI Peak Performance Buoyancy – PADI diver with buoyancy control skill
• Panic – Sudden overwhelming sensation of fear
• Parachute lift bag – Open bottomed airtight bag used for underwater buoyant lifting when filled with air
• Partial pressure – Pressure of a component gas in a mixture
• Partial pressure blending – Gas blending based on pressure ratio of components
• Partial pressure vacancy – Physiological effect of metabolism on the total dissolved gas concentration in venous blood
• PASKAL – Special operations force of the Royal Malaysian Navy
• Passive addition semi-closed circuit rebreather, also known as passive addition rebreather – Dumps gas from the breathing circuit and makes up volume on demand
• Patent foramen ovale – A heart defect present at birth
• Pearl hunting – Collecting pearls from wild molluscs
• Pearling in Western Australia – Local aquaculture industry
• Pendulum rebreather – Configuration using biderctional gas flow
• Pendulum search – Diver search pattern
• Penetration dive – Dive under a physical barrier to a direct vertical ascent to the surface
• Penetration diving – Diving under a physical barrier to a direct vertical ascent to the surface
• Peress, Joseph Salim – Pioneering British diving engineer
• Performance Freediving International (PI) – Freediver training agency
• Perfusion – Passage of fluid through the circulatory or lymphatic system to an organ or tissue
• Permanent set – Plastic deformation
• Permeation – Penetration of a liquid, gas, or vapor through a solid
• Permit-to-work – Work safety management system
• Personal diving equipment – Underwater diving equipment worn by the diver
• Personal protective equipment – Equipment designed to help protect an individual from hazards
• Philippine Underwater Hockey Confederation – National sports association
• Phoenix International Holdings – Marine services company for underwater operations
• Physiological response to water immersion – Also known as the diving response and mammalian diving reflex
• Physiology of decompression – The physiological basis for decompression theory and practice
• Physiology of diving adaptations – Adaptations of marine vertebrates to diving
• Physiology of human diving – Influences of the underwater environment on the physiology of human divers
• Pillar valve represented by Scuba cylinder valve – Valve controlling flow of breathing gas into and out of a scuba cylinder
• Piccard, Auguste – Swiss physicist, inventor, and explorer
• Pinch point hazard – Mechanical hazard which may damage or injure by reducing a gap
• Pipeline end manifold – Termination of a rigid pipeline
• Pneumofathometer – Instrument for measuring the depth of a diver by air pressure
• Police diving – A branch of professional diving carried out by police services
• Polespear – Basic rubber launched underwater fishing spear
• Police diving – A branch of professional diving carried out by police services
• Neal W. Pollock – Canadian researcher in diving physiology and hyperbaric medicine
• Pony bottle – Small independent scuba cylinder usually carried for emergency gas supply
• Pool part of the 2011 Finswimming World Championships – International competition in Hódmezővásárhely, Hungary
• Pool part of the 2013 Finswimming World Championships – International competition in Kazan, Russia
• Porpoise (rebreather) – Australian oxygen rebreather
• Porpoise (scuba gear) – Australian scuba manufacturer
• Powerhead – Specialized firearm used underwater that is fired when in direct contact with the target
• Positive pressure breathing – Breathing gas which is at a slightly higher pressure than in the resting lung
• Positive pressure breathing apparatus – Equipment in which pressure insude the facepiece is always higher than ambient pressure
• Positive pressure open circuit breathing apparatus – Equipment allowing or assisting the user to breath in a hostile environmentPages displaying short descriptions of redirect targets
• Potable water diver – Person competent to dive in potable water systems
• Potable water diving – Underwater diving in potable water systems
• Power inflator – Low pressure gas supply valve for buoyancy compensator
• PowerSwim – Diver-powered propulsion device
• Pre-dive briefing – Meeting of the dive team to discuss details before the diving operation
• Pre-dive checks – Checks done prior to entering the water for a dive
• Pressure – Force distributed over an area
• Pressure reducing regulator – Pressure control valve that maintains the downstream pressure setting
• Pressure reduction regulator – Control valve that reduces and maintains the outlet pressure of a fluid
• Pressure swing adsorption – Method of gases separation using selective adsorption under pressure
• Pressure-tight zipper – Zip fastener capable of a seal across a gas pressure difference
• Pressure transmitter (diving) – Cylinder pressure transducer with wireless transmitter linked to dive computer
• Pressure vessel for human occupation – Container to be occupied by one or more people with an internal pressure different from outside
• Priz-class deep-submergence rescue vehicle – Russian submersibles
• Professional Association of Diving Instructors (PADI) – Recreational diver training and certification agency
• Professional Divers' Association of Australia – Trade union
• Professional diving, also known as Occupational diving – Underwater diving where divers are paid for their work
• Professional Diving Instructors Corporation (PDIC) – Recreational diver training and certification agency
• Professional scuba diver – Person with skills and knowledge required for occupational diving
• Professional Technical and Recreational Diving – Diver certification agency
• Protection of Military Remains Act 1986 – UK legislation protecting wreckage of military ships and aircraft
• Protection of Wrecks Act 1973 – UK legislation on conservation of shipwrecks
• Psychological fitness to dive – Psychological fitness of a person to function safely underwater under pressure
• Psychosocial hazard – Occupational hazard to one's psychological well-being
• Psychrometric constant – Relation of the partial pressure of water in air to temperature
• Public safety diver – Diver working in the public safety sector
• Public safety diver training – Training divers for public safety services
• Public safety diving – Underwater work done by law enforcement, rescue and search and recovery teams
• Pulmonary barotrauma – Lung over-pressure and squeeze injuries
• Pulmonary circulation – Part of the circulatory system which carries blood from heart to lungs and back to the heart
• Pulmonary edema of immersion – Body fluid in the lungs while immersed
• Pulmonary oxygen toxicity – Lung injury due to nlong term exposure to high oxygen levels
• Pulmonary volutrauma – Lung injury due to over-expansion
• Purge button – Manual activation control of the demand valve
• Pyle stop – Type of short deep decompression stops in addition to the standard profile
• Pyle, Richard – American ichthyologist and scuba diver

Q

• Quintana Roo Speleological Survey – Data repository for explored sites within the state of Quintana Roo

R

• R-2 Mala-class swimmer delivery vehicle – 2-man wet sub swimmer delivery vehicle class of the Yugoslavian, and later, Croatian, Navies
• Raid on Alexandria (1941) – Italian frogman raid on British warships
• Raid on Algiers – Italian frogman raid on Allied ships in Algiers harbour in 1942
• Rash guard, also known as Rash vest – Stretch garment for protection from abrasion, UV and stings
• Ratchet reel (diving) – Type of reel used by divers to deploy and recover line
• Ratio deco – Rule of thumb for estimating a decompression schedule for a given set of breathing gases
• Ratio decompression – Rule of thumb for estimating a decompression schedule for a given set of breathing gases
• Rawlins, John – Royal Navy officer and pioneer in the field of diving medicine
• Rebreather – Portable apparatus to recycle breathing gas
• Rebreather Association of International Divers – Recreational diver training and certification agency
• Rebreather diver – Scuba diving qualification to use a rebreather
• Rebreather diving – Underwater diving using self contained breathing gas recycling apparatus
• Rebreather head-up display – User information interface always in view of the diver
• Rebreather loop – Ambient pressure breathing gas circuit
• Rebreather scrubber – Component that removes carbon dioxide from exhaled gas
• Reclaim helmet – Diving helmet that returns exhaled gas through a hose for recycling
• Reclaim regulator – Diving regulator controlling flow of exhaled gas into low pressure exhaust return hose
• Reclaim valve – Backpressure regulator controlled relative to ambient pressure for breathing gas recovery
• Recompression (disambiguation) – Returning to a state of higher ambient pressure
• Recompression chamber – A hyperbaric chamber used to treat divers suffering from decompression illness
• Recovery breathing – Brearhing technique used by free divers on surfacing to reduce the risk of surface blackout
• Recovery of a convulsing diver – Procedure for rescue of a convulsing scuba diver from underwater
• Recovery of an unresponsive diver – Procedure for rescue of a convulsing casualty from underwater
• Recreational dive – Underwater dive done for recreational purposes
• Recreational Dive Planner – PADI no-decompression dive table also available as a circular slide rule and electronic calculator
• Recreational dive sites – Places that divers go to enjoy the underwater environment
• Recreational diver certification – Certification as competent to dive to a specified standard
• Recreational diver certification agency – Agencies which issue certification for competence in recreational diving skills
• Recreational diver impact on reefs – Effects of scuba diving on the underwater environment
• Recreational diver training – Training process for people who do not dive at work
• Recreational divers – People who engage in underwater diving for entertainment
• Recreational diving – Diving for the purpose of leisure and enjoyment, usually when using scuba equipment
• Recreational diving fatalities – Deaths occurring during scuba dives
• Recreational diving instructor – Person who trains and assesses recreational divers
• Recreational diving tourism – Industry based on recreational diver travel
• Recreational scuba certification levels – Competence represented by recreational scuba certification
• Recreational scuba diving – Diving for leisure and enjoyment while using scuba equipment
• Reduced gradient bubble model – Decompression algorithm
• Redundancy (engineering) – Duplication of critical components to increase reliability of a system
• Redundant breathing gas supply – Scuba breathing gas reserved for an emergency
• Reef – A shoal of rock, coral or other sufficiently coherent material, lying beneath the surface of water
• Reef Ball Foundation – Non-profit organization to promote artificial reef building
• Reef Check – International NGO for reef conservation
• Reef Life Survey (RLS) – Marine life monitoring programme based in Hobart, Tasmania
• Refresher course – Training to update existing skills and knowledge
• Refresher training – Training to update existing skills and knowledge
• Refresher training (diving) – Checkout of skills or remedial training to bring skills back up to standard
• Regulator freeze – Underwater breathing apparatus malfunction
• Regulator freezing – Locking of a diving regulator by ice formation
• Regulator malfunction – Failure modes for diving regulators
• Remotely operated underwater vehicle (ROUV or ROV) – A tethered underwater mobile device operated by a remote crew
• REMUS (AUV) – Autonomous underwater vehicle seriesPages displaying short descriptions of redirect targets
• Repetitive dive – Dive made while outgassing from a previous dive is incomplete
• Repex – Repeated exposure to potentially toxic concentrations of oxygen in breathing gas
• Rescue bell – Diving bell for submarine rescue
• Rescue diver – Recreational scuba certification emphasising emergency response and diver rescue
• Rescue Diver – Recreational scuba certification emphasising emergency response and diver rescue
• Rescue tether – Short rope with a clip at the end attached to diver's harness to support a casualty in a rescue
• Rescue ventilation – Assisted breathing to support life
• Reserve gas supply (diving) – Surface breathing gas supply for diving use if main supply is compromised
• Reserve valve – Valve isolating access to reserve gas supply
• Residual inert gas tissue loading – Gas remaining in the tissues after decompression
• Residual nitrogen – Excess nitrogen remaining in body tissues after surfacing from a dive
• Residual nitrogen time – Estimate of excess nitrogen remaining in tissues before repetitive dive
• Resort diving – Introductory scuba diving experience
• Respiration (physiology) – Exchange of gases between environment and tissues
• Respiratory exchange ratio – Ratio between the metabolic production of carbon dioxide and the uptake of oxygen
• Respiratory gas exchange – Process by which gases diffuse through a biological membrane
• Respiratory interface – Facepiece of a breathing apparatus
• Respiratory quotient – Ratio of carbon dioxide produced by the body to oxygen consumed by the body
• Restriction (diving) – Space through which it is possible to pass with some difficulty
• Reverse squeeze – Failure of the Eustachian tubes to open during a reduction in ambient pressure
• Rip current – Water current moving away from shore
• Risk assessment – Estimation of risk associated with exposure to a given set of hazards
• Risk control – Process in which identified risks are reduced or mitigated
• Risk management – Identification, evaluation and control of risks
• RN Diving Manual – Training and operations manual
• Rock bottom gas planning – Scuba gas planning based on a planned dive profile
• Rocky reef – Natural reef of rock
• Röjdykare – Clearance divers of the Swedish Navy
• ROUV – Remotely operated underwater vehicle
• ROV KIEL 6000 – Remotely operated vehicle built by Schilling Robotics, Davis, California for scientific tasks
• ROV PHOCA – Remotely operated underwater vehicle of the COMANCHE type
• ROV Supervisor – A senior ROV pilot appointed to supervise the ROV team
• Royal Australian Navy School of Underwater Medicine (RANSUM) – Unit based in Sydney, Australia.
• Royal Engineers – Engineering arm of the British Army
• HMS Royal George (1756)#Salvage attempts – 100-gun first-rate Royal Navy ship of the line (1756) – Early salvage operation using bells and surface supplied divers
• Royal Navy ships diver – Category of underwater diver in the Royal Navy
• Rubicon Foundation – Non-profit organization for promoting research and information access for underwater diving
• Rule of thirds (diving) – Rule of thumb for scuba gas management
• Russian commando frogmen – Tactical scuba diving unit
• Russian deep submergence rescue vehicle AS-28 – Priz-class deep-submergence rescue vehicle of the Russian Navy
• Russian submarine AS-34 – Priz-class deep-submergence rescue vehicle
• Russian submarine Losharik – Russian deep-water nuclear submarine

S

• Safety culture – Attitude, beliefs, perceptions and values that employees share in relation to risks in the workplace
• Safety data sheet, also known as Material safety data sheet – Sheet listing work-related hazards
• Safety sausage – Inflatable buoy used by a diver at the surface to indicate position to the dive boat
• Safety stop – Optional decompression stop to reduce decompression stress
• Salt water aspiration syndrome – Rare diving disorder caused by inhaling a mist of seawater
• Salvage diving – Diving work associated with the recovery of vehicles, cargo and structures
• Sappers Divers Group – Portuguese Navy's diving unit
• Saturation diver – Diver registered as competent for saturation diving
• Saturation diving – Diving decompression technique
• Saturation diving skills – Skills and procedures required for the safe operation and use of saturation diving equipment
• Saturation diving system – Facility for supporting saturation diving projects
• Saturation spread – The topside base for saturation diving operations
• Saturation system – Diving decompression system
• Save Ontario Shipwrecks (SOS) – A provincial heritage NGO in Ontario, Canada
• S-BRUV – Stereoscopic baited remote underwater video
• Science of underwater diving – Scientific concepts that are closely associated with underwater diving
• Scientific diver training – Training divers who will be doing scientific work underwater
• Scientific diving – Use of diving techniques in the pursuit of scientific knowledge
• SCMBA – British military rebreather
• Scorpio ROV – Work class remotely operated underwater vehicle
• Scottish Sub Aqua Club (ScotSAC) – Scottish recreational diver training and certification agency
• Screw gate carabiner – Carabiner snap hook with screw lock gate
• Scrubber breakthrough – Failure mode in rebreathers when the carbon dioxide scrubber is exhausted
• Scuba configuration – The arrangement of self contained breathing apparatus carried by a diver
• Scuba contents gauge – Submersible pressure gauge for scuba cylinders
• Scuba cylinder valve – Valve controlling flow of breathing gas into and out of a scuba cylinder
• Scuba diving – Swimming underwater, breathing gas carried by the diver
• Scuba diving fatalities – Deaths occurring while scuba diving or as a consequence of scuba diving
• Scuba diving in the Cayman Islands – Recreational diving tourism destination
• Scuba Diving International (SDI) – Recreational diver training and certification agency
• Scuba diving quarry – Disused and flooded quarry repurposed for underwater diving
• Scuba diving skills – The skills required to dive safely using self-contained underwater breathing apparatus
• Scuba diving therapy – Treatment using scuba diving activities
• Scuba diving tourism – Industry based on recreational diver travel
• Scuba Educators International (SEI) – Recreational diver training and certification agency
• Scuba equipment – Equipment needed for scuba diving
• Scuba fatalities – Deaths occurring while scuba diving or as a consequence of scuba diving
• Scuba finswimming – Underwater sport discipline
• Scuba gas blender – Person competent to blend breathing gases for scuba diving
• Scuba gas consumption – Breathing gas used while scuba diving
• Scuba gas management – Logistical aspects of scuba breathing gas
• Scuba gas planning – Estimation of breathing gas mixtures and quantities required for a planned dive profile
• Scuba gas reserve – Breathing gas reserved for contingencies
• Scuba gear – The equipment used by a scuba diver for diving
• Scuba harness – Equipment for supporting a scuba set on a diver
• Scuba isolation manifold – Component used to functionally connect scuba cylinders
• Scuba manifold – Scuba component used to functionally connect diving cylinders
• Scuba mouthpiece – Bite grip breathing interface on demand valve
• Scuba orienteering – Underwater compass navigation and speed competition on scuba.
• Scuba regulator – Mechanism that controls the pressure of a breathing gas supply for scuba diving
• Scuba replacement – Surface-supplied diving where primary and reserve gas supplies are from high-pressure cylinders
• Scuba reserve valve – Scuba gas supply valve which is opened to release the gas held in reserve
• Scuba Schools International (SSI) – Recreational scuba and freediving training and certification agency
• Scuba set – Self-contained underwater breathing apparatus
• Scuba skills – The skills required to dive safely using a self-contained underwater breathing apparatus.
• Scubapro – Brand of scuba diving equipment
• SDBA – Special duty oxygen breathing apparatus, a military rebreather.
• Seabed mining – Mineral recovery from the bottom of the sea
• Seabed tractor – Special purpose class of remotely operated underwater vehicle
• Sea Dragon-class ROV – Chinese deep diving work class remotely operated underwater vehicle
• Seafox drone – Remotely operated anti-mine marine drone
• Seaglider – Deep diving autonomous underwater vehicle for long term missions
• SeaKeys – Collaborative marine biodiversity project in South Africa
• SEALAB – Experimental underwater habitats developed by the United States Navy
• SEAL Delivery Vehicle – Manned wet submersible for deploying naval special forces
• Sea level atmospheric pressure – Static pressure exerted by the weight of the atmosphere at sea level
• SeaPerch – Remotely operated underwater vehicle educational program
• Sea Pole-class bathyscaphe – Chinese bathyscaphe class
• Sea Research Society – American nonprofit for marine research
• SEAL Delivery Vehicle (SDV) – Manned wet submersible for deploying naval special forces
• Search and recovery diver – Diver certified as trained in underwater search and recovery
• Willard Franklyn Searle – US Navy ocean engineer and developer of diving and salvage equipment and systems
• Seasickness, also known as Motion sickness – Motion sickness occurring at sea
• Self-reliant diving – Philosophy and practice of diving that does not rely on assistance
• Self-sufficient diving – Scuba diving with skill and equipment to manage most contingencies without assistance
• Semi-submersible platforms – Marine vessel used in offshore roles wtth good stability and seakeeping
• Sentry (AUV) – Autonomous underwater vehicle made by Woods Hole Oceanographic institution
• Sewer diving – Diving for maintenance work in sewers
• Shadow Divers – Book by Robert Kurson recounting the discovery of a World War II German U-boat wreck
• Shallow water blackout – Loss of consciousness at a shallow depth during a dive
• Shallow Water Combat Submersible – Manned submersible and a type of swimmer delivery vehicle
• Shallow water helmet – Free-flow diving helmet for shallow work
• Shallow-water blackout – Loss of consciousness at a shallow depth during a dive
• Shallow-water diving helmet – Open-bottom diving helmet held on by weight
• Shark baiting – Attracting sharks by chumming the water
• Shark cage diving – Diving inside a protective cage to observe sharks in the wild
• Shark-proof cage – A metal structure to protect divers and snorkellers from potentially dangerous sharks
• Shark River Reef – Artificial reef off New Jersey
• Shark tourism – Tourism industry based on viewing wild sharks
• Shayetet 13 – Special operations unit of the Israeli Navy
• Shearwater Research – Canadian manufacturer of dive computers and rebreather electronics.
• Shilling, Charles Wesley – U.S. Navy physician, researcher, and educator
• Ships husbandry – Maintenance and upkeep of ships
• Ships husbandry diving – Diving related to the maintenance and upkeep of ships
• Shot-line, also known as shot line or shotline – Substantial weighted near-vertical line with buoy
• Sidemount – Diving equipment configuration where scuba sets are clipped to the diver's sides
• Sidemount diver – Scuba certification for using scuba sets clipped to the sides of the harness
• Sidemount diving – Diving using equipment configuration where scuba sets are clipped to the diver's sides
• Side-mount scuba – Scuba sets carried clipped to the sides of the diver's harness
• Side-slung bailout set – Bailout cylinder clipped to the side of the diver's back-mount cylinder harness
• Siebe, Augustus – German-born British engineer mostly known for his contributions to diving equipment
• Siebe Gorman – British manufacturer of diving equipment and salvage contractor
• Siebe Gorman CDBA – Type of diving rebreather used by the Royal Navy
• Siebe Gorman Salvus – Industrial rescue and shallow water oxygen rebreather
• Signal tube – Inflatable buoy used by a diver at the surface to indicate position to the dive boat
• List of signs and symptoms of diving disorders – Evidence of physiological disorders resulting from underwater diving
• Silt out – Reduction of underwater visibility by disturbing silt deposits
• Silt out, also known as siltout, or silt-out – Reduction of underwater visibility by disturbing silt deposits
• Silt screw – A peg for insertion into soft sediment to locate a distance line
• Single atmosphere diving suit – Articulated pressure resistant anthropomorphic housing for an underwater diver
• Single-hose – Mechanism that reduces pressure of a gas supply and provides it to the diver at ambient pressure
• Single-hose diving regulator – Mechanism that reduces pressure of a gas supply and provides it to the diver at ambient pressure
• Single point of failure – A part whose failure will disrupt the entire system
• The Silent World: A Story of Undersea Discovery and Adventure – Book by Jacques-Yves Cousteau and Frédéric Dumas
• Siluro San Bartolomeo – Italian manned torpedo design of late WWII
• Single point of failure – A part whose failure will disrupt the entire system
• Sinking of MV Conception – 2019 maritime disaster
• Sinking of the Rainbow Warrior – 1985 covert attack by French foreign intelligence service on a Greenpeace ship
• Sinking ships for wreck diving sites – Scuttling old ships to produce artificial reefs
• Sinus squeeze – Barotrauma of the sinuses
• Sistema Huautla – Cave system in the southern Mexican state of Oaxaca
• Sistema Nohoch Nah Chich – Flooded cave system in Mexico
• Sistema Ox Bel Ha – Flooded cave system in Quintana Roo, Mexico
• Situation awareness – Adequate perception of environmental elements and external events
• Siva (rebreather) – Range of military rebreathers
• SJT-class ROUV – Series of Chinese remotely operated underwater vehicles
• Skandalopetra diving – Freediving using a stone weight at the end of a rope to the surface
• Skindiving (disambiguation)
• Sladen Suit – Early British military drysuit
• Sling (rigging) – Rope, webbing, wire or chain used to support a load for lifting
• Sling cylinder – An independent scuba set carried clipped to the side rings of a scuba diver's harness
• Slingshot valve – Dual outlet scuba cylinder valve with Y-shape body
• Smith, Gordon – Inventor of KISS diving rebreather, born 1950
• Snag-line search – Use of a taut line towed across the search area to catch on the target
• Snell's law, also known as Law of refraction – Formula for refraction angles
• Snoopy loop, also known as ranger band – Rubber band made from inner tube
• Snorkel – Tube for breathing face down at the surface of the water
• Snorkel mask – Breathing apparatus for surface swimming
• Snorkeling – Swimming while breathing through a snorkel
• Snorkeling vest, also known as snorkelling vest – Peronal buoyancy aid for use while snorkeling
• Snuba – Limited depth airline breathing apparatus towed by the diver
• Society for Underwater Historical Research – Amateur maritime archaeology organisation in South Australia
• Solo diver – SDI recreational diver self-sufficiency certification
• Solo diving – Recreational diving without a dive buddy
• Solubility – Capacity of a substance to dissolve in a solvent in a homogeneous way
• Solution – Homogeneous mixture of a solute and a solvent
• Sonar – Acoustic sensing method
• Sonic orifice – Orifice undergoing choked flow of a compressible medium
• South African Association for Marine Biological Research (SAAMBR) – Non profit conservation research organisation based in Durban, SA
• South African Department of Employment and Labour – Department of the South African government responsible for matters related to employment
• South African Environmental Observation Network (SAEON) – A network to perform long-term ecological research in South Africa and surrounding waters
• South African Underwater Sports Federation (SAUSF) – Official World Underwater Federation representative body in the Republic of South Africa
• South Pacific Underwater Medicine Society (SPUMS) – Publisher for diving and hyperbaric medicine and physiology
• South Pacific Underwater Medical Society Journal – Journal covering underwater and hyperbaric medicine and physiology
• Southern African Underwater and Hyperbaric Medical Association (SAUHMA) – Special interest group of the Council of the South African Medical Association
• SP-350 Denise – French two-person submarine
• Spearfisherman (company) – American diving equipment manufacturer
• Spearfishing – Hunting for fish using a spear
• Speargun – Underwater fishing implement
• Special Actions Detachment – Special operations maritime unit of the Portuguese Navy
• Special Air Service – Special forces of the British Army
• Special Air Service Regiment – Special forces unit of the Australian Army
• Special Boat Service – Special forces unit of the Royal Navy
• Special Duties Unit – Hong Kong Police tactical unit
• Special Forces Command (Turkey) – Turkish special forces group
• Special Forces Group (Belgium) – Special forces unit in the Belgian Armed Forces
• Special Operations Battalion (Croatia) – Special forces military unit
• Special Service Group (Navy) – The special operations force of the Pakistan Navy
• Special Warfare Diving and Salvage – Bangladesh Navy special operations force
• Speleonaut – Diver propulsion vehicle designed for cave exploration by a disabled diver
• Spindle (vehicle) – Ice penetrating two-stage autonomous underwater vehicle
• Spiral box search – Search pattern expanding stepwise outward from datum
• Spitcock – Valve on diving helmet to let diver spit water on inside of viewport
• Sponge diving – Diving to gather natural sponges
• Sport (shipwreck) – Tugboat wrecked in Lake Huron
• Sport diving (sport) – Underwater sport using recreational open circuit scuba equipment in a swimming pool
• SPP-1 underwater pistol – Soviet four-barreled underwater dart pistol
• SPUMS – Publisher for diving and hyperbaric medicine and physiology
• SPURV – Self propelled underwater research vehicle built in 1957 for the US Navy
• SPURV II – Special purpose underwater research vessel built to srudy submarine wakes
• Squeeze (diving) – Barotrauma of descent
• SRV-300 – Deep-submergence rescue vehicle
• Stabilizer jacket – Configuration of diving buoyancy compensator
• Stage cylinder – Diving cylinder intended to be collected for use on the return part of a scuba dive
• Staged deccompression, also known as Stage decompression – Decompression with stops ad specific depths
• Stage drop, also known as Stage-drop – Placing a scuba cylinder at the distance line for planned later use.
• Stage rigging (scuba) – Clips, cords and straps on a scuba cylinder to attach it to a diver
• Stage set (scuba) – Scuba set to be used during a stage of a dive
• Staged decompression – Ascant from dive interrupted by periods at constant depth
• Standard diving dress – Copper helmet with rubberised canvas diving suit and weighted boots
• Standard diving equipment – Copper helmet with rubberised canvas diving suit and weighted boots
• Standard diving helmet – Copper free-flow helmet system used with Standard Diving Dress
• Standard helmet – Helmet of standard diving dress
• Standard operating procedure – Set of detailed instructions to assist in workplace safety
• Standard procedure – A recommend way to do something that is known to be effective and safe
• Standby diver, also known as Stand-by diver – Diver who is ready to go to the assistance of the working diver
• Standard diving dress – Copper helmet with rubberised canvas diving suit and weighted boots
• Standard operating procedure – Set of detailed instructions to assist in workplace safety
• Star Canopus diving accident – Fatal offshore diving bell accident in 1978
• Static apnea – Stationary diving discipline of holding breath underwater
• Stena Seaspread diving accident – Saturation diving bell incident with successful rescue in the North Sea in 1981
• Stratification – Layering of a body of water due to density variations
• Stress exposure training – Training in a deliberately distracting environment
• Striver (bathyscaphe) – Chinese deep submergence vehicle
• Struggler (bathyscaphe) – Chinese deep submergence vehicle
• Sub-Aqua Association (SAA) – British recreational diver training and certification organisation
• Submarine Escape Immersion Equipment – Whole-body exposure suit that allows submariners to escape from a sunken submarine
• Submarine escape set – Self contained breathing apparatus providing gas to escape from a submerged submarine
• Submarine escape training facility – Facility used for training submariners in methods of escape from a sunken submarine
• Submarine Escape Training Facility (Australia) – Shore facility of the Royal Australian Navy
• Sub Marine Explorer – Early submarine craft
• Submarine pipeline – Pipeline that is laid on the seabed or below it inside a trench
• Submarine Products – Former British diving equipment manufacturer and distributor.
• Submarine rescue – Rescue of personnel from a disabled submarine
• Submarine Rescue Diving Recompression System – Remotely operated vehicle for rescue of personnel from sunken submarines
• Submarine rescue ship – Support ship for submarine rescue and deep-sea salvage operations
• Submersible pressure gauge – Pressure measuring instrument for underwater service
• Subskimmer – Submersible diver propulsion vehicle with inflatable buoyancy for surface use
• Subsurface (software) – Creator and lead developer of the Linux kernel (born 1969)Pages displaying short descriptions of redirect targets
• Suit squeeze – Barotrauma caused by the folds of a diving suit piching the skin
• Superoxide scrubber – Breathing gas scrubber that adds oxygen and removes carbon dioxide
• Supersaturation – State of a solution that contains more solute than can be dissolved at equilibrium
• Supervised diver – Minimum requirements for a recreational diver to dive in open water under direct supervision
• Supervised Diver – Minimum requirements for a recreational diver to dive in open water under direct supervision
• Supply lock – Small airlock to transfer supplies between areas of different pressure
• Support diver – Recreational diving equivalent of a stand-by diver
• Surface blackout – Loss of consciuosness immediately following surfacing of a freediver
• Surface decompression – Decompression in a diving chamber out of the water
• Surface decompression on oxygen – Staged decompression obligation done in a decompression chamber
• Surface marker buoy – Buoy towed by a scuba diver to indicate the diver's position
• Surface oriented diving – Underwater diving in which the diver starts and finishes at surface pressure
• Surface stand-by diver procedures – Functions of member of a professional diving team
• Surface-supplied air diver – Person competent to dive with surface-supplied breathing apparatus
• Surface-supplied breathing apparatus – Equipment to supply a diver with breathing gas at ambient pressure from the surface
• Surface-supplied diver, also known as Surface supplied diver – Underwater diver breathing gas supplied from the surface
• Surface-supplied diving – Underwater diving breathing gas supplied from the surface
• Surface-supplied diving equipment – Equipment used specifically for surface supplied diving
• Surface-supplied diving procedures – Procedures used in the safe operation and use of surface-supplied diving equipment
• Surface-supplied diving skills, also known as Surface supplied diving skills – Skills and procedures required for the safe operation and use of surface-supplied diving equipment
• Surface-supplied mixed gas diver – Person competent to dive with mixed gas from a closed bell
• Surface tension – Tendency of a liquid surface to shrink to reduce surface area
• Surface water searches – Procedures to find objects or persons lost at the surface of a body of water
• Surface tension – Tendency of a liquid surface to shrink to reduce surface area
• Surfactant – Substance that lowers the surface tension between a liquid and another material
• Surfer's ear – Common name for an abnormal bone growth within the external ear canal
• Surge (wave action) – The component of wave motion close to and parallel with the bottom
• Sustained load cracking – Metallurgical failure mode of cracking under a prolonged static load
• Suunto – Finnish manufacturer of compasses, dive computers and sports watches
• Swedish Armed Forces Diving and Naval Medicine Centre – Diver education and training; diving medicine research and development
• Swimfin – Finlike accessories worn on the feet, used for swimming, snorkeling and diving propulsion
• Swimming – Self propulsion of a person through water
• Swimming-induced pulmonary edema – Body fluid in the lungs while swimming.
• Swim-through – Short underwater tunnel with adequate clearance and obvious exit
• Systemic circulation – Portion of the cardiovascular system which transports oxygenated blood away from the heart
• Systems technician – Person related to diving systems

T

• T1200 Trenching Unit – Remotely operated seabed trenching unit
• Tactical Divers Group – Special operations force of the Argentine Navy.
• Taifib – Indonesian amphibious reconnaissance unit
• Talus cave – Cave formed by rockfall debris
• Tank weight – Ballast weight attached to a scuba cylinder
• Taravana – Decompression sickness after breath-hold diving
• Task loading – Relationship between operator capacity and the accumulated activities that must be done
• Teaching method – Principles and methods used by teachers to enable student learning
• Team redundancy – System for sharing backup equipment and skill diversity
• Technical diver training – Processes to develop skills and knowledge to dive safely for technical diving
• Technical diving – Extended scope recreational diving
• Technical Diving International (TDI) – Technical diver training and certification agency
• Technical Extended Range (TXR) – Recreational scuba and freediving training and certification agency
• Tektite habitat – Undersea laboratory and experimental habitat
• Temperate reef – Hard benthic substrate and ecosystems in cool to cold water in middle latitudes
• Temperature – Physical quantity of hot and cold
• Tension-leg platform – Type of offshore platform used in production of oil or gas
• Tesei, Teseo – Italian naval officer and pioneering military diver
• Test of pressure – Diagnostic technique to identify decompression sickness
• Testing and inspection of diving cylinders – Periodical inspection and testing to revalidate fitness for service
• Texas Finswimming Association – Official governing body for competitive and recreational finswimming in Texas
• Thalmann algorithm – Mathematical model for diver decompression
• Thalmann, Edward D. – American hyperbaric medicine specialist and decompression researcher
• Tham Luang cave rescue – 2018 international rescue in Thailand
• The Darkness Beckons – History of UK cave diving by Martyn Farr
• The Last Dive – Non-fiction book by Bernie Chowdhury about a double wreck diving fatality
• Thermal undersuit – Insulating undergarments for use with a dry suit
• Therapeutic decompression tables – Planned hyperbaric exposure profiles to treat decompression sickness
• Therapeutic recompression – Recompression to reduce symptoms of decompression illness
• Thermal balance of the diver – Body temperature regulation in the underwater diver
• Thermocline – Thermal layer in a body of water
• Thermodynamic decompression model – Early model in which decompression is controlled by volume of gas bubbles forming in tissues
• Thermodynamic model of decompression – Early model in which decompression is controlled by volume of gas bubbles forming in tissues
• Theseus (AUV) – Large autonomous underwater vehicle for laying fibre-optic cable
• The Shaft (sinkhole) – Karst feature in South Australia
• The Silent World – 1956 French documentary film co-directed by Jacques Cousteau and Louis Malle
• The Silent World: A Story of Undersea Discovery and Adventure – Book by Jacques-Yves Cousteau and Frédéric Dumas
• Three bolt equipment – Standard diving dress using three bolts to clamp the helmet bonnet to the corselet
• Three Star Diver – Fully trained and experienced recreational dive
• Through-water communications – Wireless diver voice communications equipment
• Tidal race – Fast-moving tidal flow passing through a constriction, forming waves, eddies and strong currents
• Tide – Rise and fall of the sea level under astronomical gravitational influences
• Tillman, Albert – American educator and underwater diver
• Timeline of diving technology, also known as Timeline of underwater diving technology – Chronological list of notable events in the history of underwater diving equipment
• Tissue (biology) – Group of cells having similar appearance and performing the same function
• Tissue slab decompression model – A diffusion limited series tissue decompression model
• Tissue slab diffusion model – Diffusion limited series tissue decompression model
• Torricellian chamber – Air space in a cave chamber with pressure below atmospheric
• Total Nitrogen Time – Equivalent pressure exposure estimate for a repetitive dive
• Touboulic, Pierre-Marie – French engineer, inventor and writer
• Tourism on the Great Barrier Reef – Service industry in Australia involving recreational diving
• Towboard – Underwater survey equipment used to tow a diver
• Transfer under pressure – Moving between pressurised vessels without decompression
• Travel gas – Gas breathed during the descent part of a dive
• Tremie – Equipment for underwater concrete placement
• Trial diving – Introductory scuba diving experience
• Tribonucleation – Mechanism for creation of microbubbles
• Trieste II – US Navy's second bathyscaphe
• Triger, Jacques – French geologist who invented the pressurised caisson (1801–1867)
• Trim weights (diving) – Diving weights distributed primarily to improve trim
• Trimix blender – Person competent to blend trimix breathing gases for scuba diving
• Trimix (breathing gas) – Breathing gas consisting of oxygen, helium and nitrogen
• Trimix Scuba Association (TSA) – Recreational technical scuba training and certification agency
• Trongle – Device used on submarines to help swimmers to locate a submerged submarine
• Tropical coral reef – Reefs built by warm-water coral species
• Try-dive – Supervised diving experience to try out diving or equipment
• Turbidity – Cloudiness of a fluid
• Turkish Underwater Sports Federation (TSSF), also known as Türkiye Sualtı Sporları Federasyonu – Turkish national governing body for underwater sport and lifesaving
• Twin bladder buoyancy compensator – Scuba diving buoyancy compensator with redundant air bag
• Twin-hose regulator – Scuba regulator with two ambient pressure hoses to the mouthpiece
• Type 1 wet bell – Open diving bell without onboard gas panel
• Type 2 wet bell – Diving bell with onboard gas panel
• Type 904 dive tender – Chinese class of naval diving support vessel

U

• Umbilical cable – A cable and/or hose bundle which supplies required consumables to a remote user
• Umbilical management, also known as Umbilical management (diving) – Safe handling of the diver's umbilical
• Umbilical tending – Management of the supply end of the diver's umbilical
• Uncontrolled buoyant ascent – Type of diving accident
• Uncontrolled decompression – Unplanned drop in the pressure of a sealed system
• Undersea and Hyperbaric Medical Society (UHMS) – US based organisation for research and education in hyperbaric physiology and medicine.
• Undersea Medical Society – Original name of Undersea and Hyperbaric Medical Society
• The Undersea World of Jacques Cousteau – Documentary television series about underwater marine life
• Undersuit – Clothing worn under a protective suit
• Undertow (water waves) – Return flow below (nearshore) water waves.
• Underwater – Aquatic or submarine environment
• Underwater acoustic communication – Wireless technique of sending and receiving messages through water
• Underwater acoustic positioning system – System for tracking and navigation of underwater vehicles or divers using acoustic signals
• Underwater acoustics – Study of the propagation of sound in water
• Underwater archaeology – Archaeological techniques practiced at underwater sites
• Underwater Bike Race – Annual charity event in North Carolina
• Underwater blackout syndrome – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
• Underwater breathing apparatus – Equipment which provides breathing gas to an underwater diver
• Underwater camera housing – Water and pressure resistant container for camera
• Underwater citizen science – The organised collection of underwater data for scientific purposes by volunteers
• Underwater computer vision – Subfield of computer vision
• Underwater concrete placement – Positioning freshly mixed concrete at an underwater location where it is to set
• Underwater construction – Industrial construction in an underwater environment
• Underwater Construction Teams – Navy construction battalion underwater construction units
• Underwater cutting and welding – Metalworking techniques used by underwater divers
• Underwater cycling – Stunt in which a bicycle is ridden under water
• Underwater Defence (Turkish Armed Forces) – Special operations unit of the Turkish Navy
• Underwater demolition – The deliberate destruction or neutralization of man-made or natural underwater obstacles
• Underwater Demolition Command – Special warfare unit of the Greek Navy
• Underwater Demolition Team – US Navy special operations group
• Underwater diver – Person who descends below the surface to interact with the environment
• Underwater diver training – Processes by which people develop the skills and knowledge to dive safely underwater
• Underwater divers – People who participate in underwater diving
• Underwater diving – Descending below the surface of the water to interact with the environment
• Underwater diving environment – The underwater environment to which a diver may be exposed
• Underwater diving equipment – Equipment used to facilitate underwater diving
• Underwater diving on Guam – Recreational diving tourism destination
• Underwater diving terminology, also known as Underwater diving terms – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
• Underwater domain awareness – Underwater component of maritime domain awareness
• Underwater environment – Aquatic or submarine environment
• Underwater exploration – Investigating or traveling around underwater for the purpose of discovery
• Underwater Explorers Club – British diving club, now defunct
• Underwater firearm – Firearms that can be effectively fired underwater
• Underwater football – Underwater team sport using snorkeling equipment and an American football
• Underwater habitat – Human habitable underwater enclosure filled with breathable gas
• Underwater hockey – Underwater sport of pushing a puck into the opposing goal
• Underwater hockey in Australia – History and organisation of the sport in Australia
• Underwater hockey in Turkey – History and organisation of the sport in Turkey
• Underwater Hockey Wales – Welsh underwater hockey association
• Underwater Hockey World Championships – International event for the sport of Underwater Hockey
• Underwater ice hockey – Freediving variant of ice hockey played upside-down under the ice
• Underwater inspection – Examination of underwater structure and equipment to assess condition
• Underwater mining – Any mining activity done underwater
• Underwater navigator – Diver competent to navigate in open water by compass or pilotage
• Underwater Offence (Turkish Armed Forces) – Special operations Forces of the Turkish Navy
• Underwater orienteering – Underwater compass navigation and speed competition on scuba.
• Underwater Orienteering World Championships – International sporting competition
• Underwater photography – Genre of photography
• Underwater photography (sport) – Competitive underwater digital photography on scuba
• Underwater Photography World Championships – International event for the sport of underwater photography
• Underwater Port Security System – Defense against hostile swimmer incursions
• Underwater rescue – Rescue of persons trapped underwater
• Underwater rifle – A man-portable, long-barreled firearm which can be fired effectively underwater
• Underwater rugby – Underwater team sport
• Underwater rugby in Australia – Water sport
• Underwater rugby in Colombia – Regional sporting activity
• Underwater rugby in the United States – Class of breathhold watersport
• Underwater Rugby World Championships – International sporting competition
• Underwater search and recovery – Locating and recovering underwater objects
• Underwater searches – Techniques for finding underwater targets
• Underwater Society of America (USOA) – American national representative organization for underwater sport.
• Underwater sports – Competitive underwater recreational activities
• Underwater sports at the 2013 Bolivarian Games – Finswimming, free-diving and spearfishing events at San Lorenzo island
• Underwater survey – Inspection or measurement in or of an underwater environment
• Underwater surveying – Inspection or measurement in or of an underwater environment
• Underwater target shooting – Breathhold underwater sport of target shooting with a speargun in a swimming pool.
• Underwater tending point – Place where the diver's umbilical is restrained or controlled
• Underwater vehicle – Vehicle intended to operate underwater
• Underwater videographer – Diver trained in the use of video recorders underwater
• Underwater videography – Electronic underwater photography concerned with capturing moving images
• Underwater visibility – Distance at which an object can be seen through water
• Underwater vision – The ability to see objects underwater
• Underwater warfare – One of the three operational areas of naval warfare
• Underwater work – Work done underwater during diving operations
• Underwater wrestling (disambiguation)
• Under way – State of a vessel
• United Diving Instructors (UDI) – Recreational diver training and certification agency
• United States Marine Corps Combatant Diver Course – Military diver training for the US Marines
• United States Marine Corps Force Reconnaissance – USMC deep reconnaissance unit
• United States Marine Corps Reconnaissance Battalions – Reconnaissance assets of Marine Air-Ground Task Force
• United States military divers – Underwater divers employed by the US armed forces
• United States Navy Experimental Diving Unit (NEDU) – The primary source of diving and hyperbaric operational guidance for the US Navy
• United States Navy SEALs – U.S. Navy special operations force
• United States Navy SEAL selection and training
• Universal Referral Program – System to complete recreational scuba training with another instructor
• Unmanned diving – Diving for data collection of the environment
• Upstream scuba manifold – Manifold connecting cylinders upstream of the valve
• Upwelling – Replacement by deep water moving upwards of surface water driven offshore by wind
• URF (Swedish Navy) – Swedish submarine rescue vehicle
• U.S. Divers – Manufacterer of scuba diving equipment
• User respiratory interface – Facepiece of a breathing apparatus
• US Navy decompression models and tables
• U.S. Navy Diving Manual (USNDM), also known as United States Navy Diving Manual, or US Navy Diving Manual – Training and operations handbook
• U.S. Navy Experimental Diving Unit (USNEDU, NEDU) – The primary source of diving and hyperbaric operational guidance for the US Navy
• Uwatec – Manufacturer of diving equipment

V

• Valsalva device – Pad in a helmet or mask used to block the nose to assist in ear clearing
• Valsalva maneuver – Technique for equalising pressure in the middle ears
• Variable weight apnea – Deep freediving using a weighted sled for descent, pulling along the depth rope for ascent
• Variable weight apnea without fins – Competitive freediving discipline
• Variable-buoyancy pressure vessel – Type of rigid buoyancy control device
• Varying Permeability Model – Decompression model and algorithm based on bubble physics
• Vasa (ship) – 17th-century Swedish warship
• Venture One diving accident – Saturation diving fatality in the North Sea in 1977
• Vertical Blue – Freediving competition held annually in The Bahamas at Dean's Blue Hole
• Vertigo – Type of dizziness where a person has the sensation of moving or surrounding objects moving
• VideoRay UROVs – Series of inspection class remotely operated underwater vehicles
• Viewport (diving) – Transparent part of a helmet, submersible, or diving chamber
• Vintage scuba – Early model scuba equipment and the ongoing activity of diving with it
• Volumetric gas fraction – Dimensionless quantity
• Voyage to the Edge of the World – 1976 French nature documentary
• VVAL 18 – Mathematical model for diver decompression

W

• Waage Drill II diving accident – Fatal saturation diving accident in the North Sea in 1975
• Wall diving – Underwater diving alongside a near vertical face
• WASP atmospheric diving system – Type of armoured diving suit without leg articulation
• Water polo cap – Headgear used in water polo and a number of underwater sports
• Waterproof digital camera – Digital still camera with inherently waterproof casing
• Water safety – Human safety in the vicinity of bodies of water
• Water separator – Device to remove condensed water from compressed air
• Water surface searches – Procedures to find objects or persons lost at the surface of a body of water
• Watertight zipper – Zipper closure which prevents water leakage when closed
• Waves and shallow water – Effect of shallow water on a surface gravity wave
• Wave shoaling – Effect by which surface waves entering shallower water change in wave height
• Weight – Force on a mass due to gravity
• Weight belt – A ballasted waist belt worn by a diver
• Weighted boots (diving) – Shoes with heavy metal soles used as part of a diver's weights
• Weighted shoes (diving) – Shoes with heavy metal soles used as part of a diver's weights
• Weight harness – Webbing system to support diver ballast weights
• Weight pocket – Container on diving equipment to hold ballast
• Welfreighter – British midget submarine of the Second World War
• Wells, John Morgan – Physiologist, aquanaut and researcher (1940–2017)
• Welman submarine – Second World War one-man British midget submarine
• Welsh Association of Sub Aqua Clubs – Welsh national governing body for underwater sport and recreational diving
• Wet Nellie – 1976 car-shaped submarine from the James Bond film The Spy Who Loved Me
• Wet sub – Ambient pressure diver propulsion vehicle
• Wetsuit – Garment for thermal insulation from water
• Wetsuit boots – Foam neoprene footwear for watersports
• Wetsuit buoyancy – Upwards forece generated by the volume of an immersed wetsuit
• Wetsuit buoyancy loss – Temporary reduction of volume due to compression at depth
• Wildrake diving accident – Fatal offshore diving accident in Scotland, 1979
• Willful violation – Deliberate or negligent violation of workplace rules and policies
• Wind generated current – Flow in a body of water generated by wind friction on its surface
• Wind wave – Surface waves generated by wind on open water
• Women Divers Hall of Fame – International honor society.
• Woodville Karst Plain Project (WKPP) – Project and organization to map the underwater cave systems of the Woodville Karst Plain
• Work of breathing (WOB) – Energy expended to inhale and exhale a breathing gas
• Working diver – The person who is intended to do the underwater work during a professional dive
• Workplace health surveillance – Ongoing surveillance of workers' health
• World Recreational Scuba Training Council (WRSTC) – Scuba diving standards body
• World Without Sun – 1964 film by Jacques Cousteau
• Wreck Alley – Area off California with several wrecks sunk as artificial reefs
• Wreck diving – Recreational diving on wrecks

Y

• YMCA SCUBA Program – Defunct recreational diver training and certification agency.
• Yoke connector – Clamp to connect scuba regulator to cylinder valve