A limpet mine is a type of naval mine attached to a target by magnets. It is so named because of its superficial similarity to the limpet, a type of sea snail that clings tightly to rocks or other hard surfaces.
A swimmer or diver may attach the mine, which is usually designed with hollow compartments to give the mine slight negative buoyancy, making it easier to handle underwater.
Usually limpet mines are set off by a time fuse. They may also have an anti-handling device, making the mine explode if removed from the hull by enemy divers or by explosions. Sometimes the limpet mine was fitted with a small turbine which would detonate the mine after the ship had sailed a certain distance, so that it was likely to sink in navigable channels or deep water out of reach of easy salvage. Thus, determining the cause of the sinking is more difficult.
