The Kaiten (meaning "Reverse Destiny" or "Change the World" in Japanese) was based on the Japanese Navy Type 93 torpedo and was a top secret suicide weapon developed by the Imperial Japanese Navy (IJN) for service during World War 2 (1939-1945). The IJN had suffered considerable defeats heading into 1944 and all measures were on the table to stem the tide of defeat. As such, a reworked torpedo, housing a single crew member with basic instrumentation and controls and showcasing with a 3,000lb (1,360 kg) warhead at its bow, was devised to sneak up on unsuspecting Allied warships and merchantmen. The IJN commissioned about 400 of these suicide machines with more than 100 of these sent on missions.
As well as the obvious advantage of the pilot providing guidance for the torpedo, Kaitens could be launched from a submerged submarine unlike the unmanned Type 93 torpedo which was deck-launched from the surface at no deeper than periscope depth. Mothership submarines could carry up to six suicide-minded Kaiten vehicles. The manned torpedo was launched around 8,300 yards from its intended target and, at about 550 yards away, the torpedo submerged to about 13 feet to complete the final run and give the pilot some visual awareness. However they were not nearly as effective pound-for-pound as the highly-successful Type 93 torpedo series on which they were based and used up their valuable pilots in the process.
American sources report that the only sinkings caused by Kaiten suicide attacks were the tankers USS Mississinewa and USS Underhill.