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Japanese Suicide Submarines
By Mike Bennighof, Ph.D.
December 2013

During the Second World War, the accuracy of torpedoes and air-launched missiles alike suffered from very primitive guidance systems. They could deliver huge warheads that devastated any ship they hit, but actually hit those targets fairly rarely.

U.S. Navy diagram of Kaiten Type 1 (top) and Type 2 (bottom).

The Imperial Japanese Navy attempted to solve that problem by adapting what is still the most sophisticated computer system on the planet and likely to remain so for some time: the human brain. By adding a human pilot to bombs and torpedoes, they would have a much better chance of striking their targets. To some Japanese, this dovetailed with the code of Bushido, the “Way of the Warrior.” In its traditionalist form, a practitioner should view life in retrospect, from the moment of death.

“Warriors who sacrifice their lives for the emperor will not die,” wrote Lieutenant Colonel Sugimoto Goro. “They will live forever. Truly they should be called gods and Buddhas for whom there is no life or death. Where there is absolute loyalty there is no life or death.”

Suicide as a battlefield tactic has a complicated place in the Japanese national psyche, one often difficult to understand from a Western perspective. As for effectiveness, inserting a human pilot would seem to have promise of great success (beyond the morbid aspect) but in reality obtained very limited results.

Officially, only piloted aircraft were “Kamikazes,” but they were far from the only Japanese weapon system to use a suicidal pilot. The navy also mounted cockpits on torpedoes to create the Kaiten (“Turning of the Clouds”; a taijutsu martial arts manuever) suicide miniature submarine. This was the first Japanese program to deliberately include suicide as a planned feature (both American and Japanese pilots had crashed damaged planes into enemy ships from the start of the war) but saw combat after the first Kamikaze aircraft units.

A Kaiten Type 2, captured by U.S. forces.
Proposed in mid-1943, the Kaiten program failed to gain approval until early 1944. The Kaiten Type 1 was simply a Type 93 24-inch oxygen-fueled torpedo (the famous “Long Lance”) cut in half, with a new section inserted in the middle to carry the pilot. He had a canvas seat (comfort being a secondary consideration on a one-way mission) and a small periscope. The Type 93 already had a massive warhead compared to other nations’ torpedoes; the Kaiten carried one more than three times its size. If the suicide sub actually hit its target, it could cause catastrophic results. The tiny submarine was 48 feet long, with a variable speed of 12 to 30 knots (below 12 knots, the Kaiten would sink).

Torpedoes are not designed to be tiny submarines; the Italians called their similar (though non-suicidal) weapons “pigs” for their poor handling qualities. The Japanese vessels appear to have been even harder to handle, though few pilots came back to make complaints. A new-model Kaiten appeared anyway, the Type 2. The Type 2 was seven feet longer, with a more powerful motor using hydrogran peroxide and an even larger warhead. Testing showed it more manueverable than the Type 1. The Type 4 was identical, but with simpler engineering. Only a few dozen of these types were made. The bigger Kaiten could make 40 knots, and had more range as well.

A home-made Kaiten found at Truk. Surely it would have capsized when launched.
The Type 10 was based on the smaller, 21-inch Type 92 electric torpedo carried by submarines. It was even less satisfactory. At a number of installations, crews appear to have cobbled together home-made Kaitens, jury-rigging cockpits on the backs of Long Lance torpedoes. Total Kaiten production seems to have been about 400 Type I and perhaps two dozen Types 2 and 4, plus an unknown number of field conversions.

Most Kaitens used in action were launched from submarines. The submarines carried them in special deck well, usually modified from their aircraft hangars. Very few found targets: the first successful Kaiten attack came in November, 1944, when a submarine-launched Kaiten slipped into Ulithi Atoll and rammed its charge into the fleet oiler Mississinewa. In July, 1945 a Kaiten rammed the destroyer escort Underhill, blowing the ship apart and instantly killing half her crew.

Indianapolis sets out on her last voyage, 26 July 1945.
Later that month, the submarine I-58 spotted the heavy cruiser Indianapolis, travelling unescorted from Guam to Leyte. The submarine’s captain, Mochitsuru Hashimoto, sank the target with conventional torpedoes, but periodically the claim is made that at least one Kaiten was involved. Hashimoto testified after the war that he did not launch the suicide submarines, because he forgot to issue the order to do so amid the excitement of finding such a prized target alone and unguarded.

It’s not known how many Kaiten were launched unsuccessfully during the last two years of the war, but the success ratio appears to have been vanishingly small. A number of surface ships were modified to carry Kaiten as well, from overaged destroyers to cruisers to seaplane carriers.

Can the suicide subs strike home? Order our
game Great Pacific War and find out.