The Kaiten is a modified Japanese Long Lance Torpedo, also referred to as a Human Torpedo. Kaiten translates roughly from Japanese as "To Change the World". The Kaiten's specifications are:

Length: 55 feet
Beam: 4 feet 6 inches
Crew: 1
Displacement: 18 Tons
Max Speed: 40 knots (44mph)
Armament:
 1 3,300 pound warhead
Power Plant: Type 6 Torpedo motor
Range: 83 miles

The Kaiten was a modified Japanese Long Lance Torpedo (with provision for one crew member) launched from a mother sub which carried up to 6 Kaitens for Kamikaze suicide attacks. The pilot would enter from the mother sub through a hatch in the bottom of the submarine. It was a collision with a one of these Kamikaze (meaning Divine Wind - a reference to a typhoon in 1281 that saved Japan from a Mongol invasion by ship) weapons that caused the destruction of Destroyer Escort (the USS Underhill DE-682) like my dad's (the USS Bangust DE-739), the 3300lb warhead blowing the ship in two. At the time the Underhill had sighted 2 periscopes on a collision course with the ship and prepared to ram one of the kaitens, probably not realizing the subs were in fact human torpedoes. There were 2 massive explosions after the impact. Here are 3 slightly varying accounts of the Underhill's sinking:

http://www.ussunderhill.org/html/kaiten_information.html
http://www.ussunderhill.org/html/stories-02.html
http://www.ebroadcast.com.au/lookup/encyclopedia/us/USS_Underhill_(DE-682).html

This MK II Kaiten was 55' long by 4'6" in diameter and had a top speed of 40 knots with a range of 83 miles at 20 knots. The big advantage of this Japanese Kamikaze weapon was its human guidance system and the ability to make multiple passes at a target should it miss the first time. But they were unstable and tended to porpoise up and down and were difficult to keep at depth. During the Underhill sinking one of the subs targeted an LST which should have been it's primary target but the craft went clean under the ship. Then the modified human Long Lance Torpedo came about and back towards the Underhill. Trying to pilot this Kamikaze weapon must have been even more terrifying than being targeted by one.