A semi-submersible naval vessel is a hybrid warship, that combines the properties of a surface ship and submarine by using water ballast to partially immerse and minimize its above-waterline profile, thereby improving its stealth characteristics when in hostile waters. The USS Monitor was an antecedent to such craft with its low-profile deck and gun turret. Russian and North Korean semi-submersible naval vessels evolved from torpedo boats and special forces boats that could partially submerge (sometimes to snorkel depth) to perform their missions. The US Navy SEALs use such vessels for clandestine special forces actions. Efforts to embody advantageous surface-ship characteristics into submarines have not been widely adopted.


The first US Navy ironclad ship, the USS Monitor, exhibited a low surface profile.
The first US Navy ironclad ship, the USS Monitor, exhibited a low surface profile.

USS Monitor was an iron-hulled, steam-powered warship—built during the American Civil War—as the first ironclad warship commissioned by the Union Navy. The Monitor is noted for its role in the Battle of Hampton Roads in 1862, when it fought indecisively against the casemate ironclad, CSS Virginia. The novel design of the ship, distinguished by its revolving turret and low profile, was quickly duplicated and established the monitor type of warship for use in shallow coastal waters.[1] Its low-freeboard deck—only 18 inches (46 cm) above the water—with a single gun turret gave it the appearance of a "cheesebox on a raft", according to observers of the time.[2] The designer, John Ericsson, had deliberately minimized the observable surface of the vessel and the area that it presented as a target. The Monitor was not designed to be semi-submersible, however.

True semi-submersibles

Examples of true semi-submersible naval vessels were developed in the Russian Empire, North Korea and the United States.

Russian Empire

Semi-submersible Imperial Russian Navy torpedo boat, Keta
Semi-submersible Imperial Russian Navy torpedo boat, Keta

The Imperial Russian Navy developed semi-submersible vessels—starting with the Keta [ru]—which were designed to be torpedo boats with low visibility for coastal protection against enemy warships. Keta was built in 1904 in St. Petersburg, powered by a 14-horsepower (10 kW) motor, displacing 8 tons, and with a length of 7 metres (23 ft). It saw service in 1905 during the Russo-Japanese War to protect the coast in the Far East. Keta was followed by other designs, "Variant D" and "Type F".[3]

North Korea

See also: Kajami-class torpedo boat and Gahjae-class torpedo boat

According to the Covert Shores Naval Warfare Blog, North Korea's Korean People's Navy developed semi-submersible for infiltration of agents and use by special forces. These derived from high-speed surface craft, sometimes disguised as fishing vessels. The I-SILC model was the first semi-submersible, which could submerge to snorkel depth to power its combustion engine. Approaching its insertion point, the vessel operates as a planing power boat. This evolved into two models of Taedong semi-submersibles, the B and C models, which were exported to Vietnam and Iran. The Taedong–C is a semi-submersible variant of the IPS-16 Peykaap torpedo boat.[4] North Korean semi-submersibles have been intercepted while making incursions into South Korean waters.[5]

In 2002, North Korea delivered five Taedong semi-submersible vessels to the Iranian Navy as part of an arms shipment that included other types of gunboats and patrol boats.[6]

United States

Naval Special Warfare Command SEALION II
Naval Special Warfare Command SEALION II

In 2014, the United States Naval Special Warfare Command (NAVSPECWARCOM) unveiled its SEAL Insertion, Observation, and Neutralization (SEALION) craft, designed and built as a Combatant Craft Heavy (CCH). The craft is designed for low radar observability and can carry crew and payload internally. At that time there were two units operational, with a third one ordered for delivery in 2018.[7] The SEALION is reportedly a semi-submersible with a planing hull for surface running and ballast tanks to run with a reduced profile. Its dimensions are 80 feet (24 m) long, 14.5 feet (4.4 m) abeam, and 9.5 feet (2.9 m) from keel to cabin roof. It displaces 80,000 pounds (36 t) and is powered by two ten-cylinder, 1,500-horsepower (1,100 kW) diesel engines. Its aft payload bay is configured to accommodate either two inflatable boats, one special forces modified jet ski, or eight seats.[8]

Submarine hybridization

French submarine, Surcouf with heavy artillery
French submarine, Surcouf with heavy artillery

As a related development, the hybridization of submarines to acquire certain surface ship attributes has included the augmentation of firepower and surface speed.


Cruiser submarines combined the stealth of a submarine with the endurance and firepower of a surface ship; several were the largest submarines built at the time of their launching. They were designed to attack merchant marine shipping with heavy deck guns, as well as torpedoes. They were generally slower to dive and offered a bigger sonar signature than conventional submarines. Examples are:[9]


SMX-25, a French design concept for a submarine that travels at high speed on the surface to arrive in theater.
SMX-25, a French design concept for a submarine that travels at high speed on the surface to arrive in theater.

Before the advent of nuclear power, submarines were slower on the surface than surface ships and even slower underwater.[14] Therefore, efforts were made to increase submarine surface speeds to that of surface-only ships. Examples:

See also


  1. ^ Silverstone, Paul H. (2006). Civil War Navies 1855–1883. The U.S. Navy Warship Series. New York: Routledge. ISBN 0-415-97870-X.
  2. ^ Thulesius, Olav (2007). The Man who Made the Monitor: A Biography of John Ericsson, Naval Engineer. Jefferson, North Carolina: McFarland & Company. ISBN 978-0-7864-2766-6.
  3. ^ Rassol, I.R. (2005), Полуподводные лодки лейтенанта С. А. Яновича [Semi-submersible boats of Lieutenant S.A. Yanovich] (in Russian), Центр технологии судостроения и судоремонта (Center for Shipbuilding Technology and Ship Repair), pp. 74–80
  4. ^ KZ (July 1, 2010). "North Korean Semi-submersible craft". Covert Shores Naval Warfare Blog. Retrieved 2017-04-21.
  5. ^ Cho, Seong-Tae (1999). "Defense White Paper". Republic of Korea: Ministry of National Defense. Retrieved 2017-04-21. ((cite journal)): Cite journal requires |journal= (help)
  6. ^ "N. Korea delivers semi-submersible gunships to Iran". Washington Times. Washington, DC. December 16, 2002. Retrieved 2017-04-22.
  7. ^ Gourley, Scott R. (July 18, 2014). "NSW Maritime Mobility". www.defensemedianetwork.com. Defense Media Network. Retrieved 2017-04-21. SEAL Insertion, Observation, and Neutralization (SEALION) craft. NAVSPECWARCOM has operationalized two technology demonstrators and would like to procure a third SEALION. NAVSPECWARCOM photo
  8. ^ Sutton, H.I. (February 13, 2017). "SEALION and Alligator stealth boats". www.hisutton.com. Covert Shores. Retrieved 2017-04-21.
  9. ^ Blair, Clay (1996). Hitler's U-Boat War. Vol. The Hunters 1939-1942. New York: Random House. ISBN 0-394-58839-8.
  10. ^ Gröner, Erich; Jung, Dieter; Maass, Martin (1991). U-boats and Mine Warfare Vessels. German Warships 1815–1945. Vol. 2. Translated by Thomas, Keith; Magowan, Rachel. London: Conway Maritime Press. ISBN 0-85177-593-4.
  11. ^ Brown, David K. (1982). "X1-Cruiser Submarine". In John Roberts (ed.). Warship VI. Vol. VI. London: Conway Maritime Press. pp. 232–233. ISBN 0-85177-265-X.
  12. ^ Winchester, Clarence (1937). Shipping wonders of the world. Vol. 41–55. Amalgamated Press. p. 1431.
  13. ^ a b Yakubov, Vladimir; Worth, Richard (2008), Raising the Red Banner: The Pictorial History of Stalin's Fleet, 1920-1945, Spellmount, p. 223, ISBN 9781862274501
  14. ^ Sandler, Stanley (2001). World War II in the Pacific: An Encyclopedia. Taylor & Francis. p. 660. ISBN 9780815318835.
  15. ^ Everitt, Don (1963). The K Boats. London: George Harrap
  16. ^ Aframeev, E.A. (1998). "Проект 1231 опытного малого погружающегося ракетного корабля" [Project 1231 - Experimental submersible missile boat] (PDF). военно-технический сборник «Невский бастион» (in Russian). 2: 22–28. Retrieved 26 February 2013.
  17. ^ Barreira, Victor M.S. (2010), Verma, Bharat (ed.), "Developments in French Naval Industry", Indian Defense Review, Lancer, 25 (4): 188, ISBN 9788170621829