Limpet
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. The limpet mine was developed and first prototyped in June/July 1939 by Macrae and Clarke. The two men visited Woolworths and they got washing-up bowls made of spun aluminum to contain the explosives. They then raided all the sweet shops in Bedford for aniseed balls that were used as a time delay for setting off the explosives so that the saboteurs, frogmen who were attaching these limpet mines to the side of enemy ships, could have a safe time to escape before the charges went off.
A frogman would be loaded up with the limpet mines before swimming to the side of a ship, and plant the charge against the side using magnets on the underside of the limpet mine, hence the curved shape with the magnets underneath, it looked like a giant limpet when it was attached to the hull of a ship. The limpet mines saw many uses during World War II. Even today, limpets are used, sometimes simply as red hearings.
One of the most dramatic examples of the use of a limpet mine was during Operation Jaywick, a special operation undertaken in September 1943 during which fourteen Allied commandos raided Japanese shipping in Singapore Harbor. They paddled into the harbor and placed limpet mines on several Japanese ships before escaping. In the resulting explosions, the limpet mines sank or seriously damaged seven Japanese ships, comprising over 39,000 tons among them.
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