A minelayer is any warship, submarine or military aircraft deploying explosive mines. Since World War I the term "minelayer" refers specifically to a naval ship used for deploying naval mines. "Mine planting" was the term for installing controlled mines at predetermined positions in connection with coastal fortifications or harbor approaches that would be detonated by shore control when a ship was fixed as being within the mine's effective range.
Before World War I, mine ships were termed mine planters generally. For example, in an address to the United States Navy ships of Mine Squadron One at Portland, England, Admiral Sims used the term “mine layer” while the introduction speaks of the men assembled from the “mine planters”. During and after that war the term "mine planter" became particularly associated with defensive coastal fortifications. The term "minelayer" was applied to vessels deploying both defensive- and offensive mine barrages and large scale sea mining. "Minelayer" lasted well past the last common use of "mine planter" in the late 1940s.
An army's special-purpose combat engineering vehicles used to lay landmines are sometimes called "minelayers".
Beginning in World War II, military aircraft were used to deliver naval mines by dropping them, attached to a parachute. Germany, Britain and the United States made significant use of aerial minelaying.
A new type of magnetic mine dropped by a German aircraft in a campaign of mining the Thames Estuary in 1939 landed in a mudflat, where disposal experts determined how it worked, which allowed Britain to fashion appropriate mine countermeasures.
The British Royal Air Force minelaying operations were codenamed "Gardening". As well as mining the North Sea and approaches to German ports, mines were laid in the Danube River near Belgrade, Yugoslavia, starting on 8 April 1944, to block the shipments of petroleum products from the refineries at Ploiești, Romania.
"Gardening" operations by the RAF were also sometimes used to assist in code breaking activities at Bletchley Park. Mines would be laid, at Bletchley Park's request, in specific locations. Resulting German radio transmissions were then monitored for clues which could help deciphering messages encoded by the Germans using Enigma machines.
In the Pacific, the US dropped thousands of mines in Japanese home waters, contributing to that country's defeat.
Aerial mining was also used in the Korean and Vietnam Wars. In Vietnam, rivers and coastal waters were extensively mined with a modified bomb called a destructor that proved very successful.
Some examples of minelaying vehicles: