British "Chariots" (swimmer vehicles)
Human torpedoes or manned torpedoes were secret naval weapons of World War II. The name is most commonly used to refer to the weapons that Italy and later Britain deployed in the Mediterranean and used to attack ships in enemy harbours. See also frogman.
These were electrically propelled torpedoes with two crewmen equipped with diving suits riding astride. They steered the torpedo at slow speed to the enemy ship. The detachable warhead was then used as a limpet mine. They then rode the torpedo away.
http://en.wikipedia.org/wiki/Manned_torpedo