The world was horrified to hear of tragic accounts of suicide kamikaze attacks on US Navy vessels at the end of World War II but most people do not know of their ocean-going counterpart the kaiten. Kaiten were manned torpedoes that functioned as the equivalent of an airborne kamikaze but operating underwater. People would crawl into armed tubes and given just enough oxygen to live for but a few moments and gyroscope and launched towards enemy ships.

Between kamikaze planes, hopeless banzai charges, and the kaiten the Japanese zealotry for honorable suicide seems to have few boundaries.

But the kaiten is far more terrifying than the former.

A tiny one-way submersible

Manned torpedoes were not a Japanese invention, they had been used in the Mediterranean for many years. However, the original European manned torpedoes were not suicide devices, they were used for sabotage, reconnaissance, and other similar covert operations but the pilots were always meant to survive.

As desperation mounted in Japan for results, more drastic measures were ordered to be taken. Failure was no longer an option. Every torpedo that missed its mark was a stain on Japanese honor and a missed opportunity. As the Americans lined up for a naval encirclement and potential invasion of Japan’s outlying islands and eventually home islands, success at sea became imperative to Japanese survival.

In 1944, the kaiten began development in Japan. By summer of that same year one hundred units were ordered.

The kaitens were modified versions of the successful Type 93 torpedo that the Japanese had deployed to great effect throughout the course of the war. The propulsion section of a Type 93 was mounted to a small pod that held the pilot. The pilot had a small amount of oxygen, a gyroscope, and a periscope. The pilot’s entire purpose was to live long enough to guide the torpedo to its target and detonate.

The kaiten was equipped with a 3,420-pound warhead which was nearly three times the size of a standard torpedo warhead.

Once sealed, there was no way for the pilot to exit the craft.

These manned torpedoes were used by a variety of Japanese vessels but only submarines used them in combat. In total twenty-four submarines, fourteen Matsu-class destroyers, and one light cruiser were equipped to launch kaiten torpedoes.

Successes and failures

In 1944, the kaiten program opened itself to applicants. Japanese soldiers were not forced to board these suicide vessels — they volunteered by the thousands. But despite the overwhelming enthusiasm for the program (they had every open spot filled within days), it was not the success that the Japanese military designers had envisioned.

At first glance, the kaiten should have been more effective than the Type 93 torpedo as it had a human driver. However, the submersibles were prone to leaking, malfunctions, and premature detonations that rendered them less effective than their unmanned counterpart.

Only two ships of note were claimed to have been sunk by manned torpedoes, the USS Mississinewa, a refueling ship, and a destroyer the USS Underhill. The US Navy attributed 187 deaths to kaiten operations which came at the cost of 106 Japanese lives, not a great tradeoff for an entire division of new warfare.

What the Japanese did not account for was that the kaiten were slower, larger, and had to run shallower than Type 93 torpedoes which often gave the position of the parent submarine away. Estimates put the number of Japanese submarines found and destroyed because of the use of kaiten torpedoes at eight which led to nearly 1,000 extra deaths on the Japanese side.

Legacy

Today, the kaiten manned torpedoes are largely forgotten. There is a museum dedicated to their losses and service in the Japanese prefecture where they were tested. They stand as a stark reminder of the great lengths the Japanese high command and individual soldiers would go through in order to protect their nation from external threats.

In the realm of suicide devices, this ranks as one of the most terrifying. Being trapped underwater with hardly any air and the only way out being a button that detonated a two-ton warhead sounds simply awful.

Kaitens reported many cases of malfunction and premature detonation which some historians have attributed to pilot action rather than an error. They speculate that instead of turning the torpedo around in the case of a miss, as intended, many kaiten pilots simply detonated their warheads as soon as possible to avoid being trapped in a metal cylinder underwater for any longer than absolutely necessary.

At least in the seat of a kamikaze you could see the sky above, the sea below, and the target clearly. The plane was at your fingertips. In a kaiten there were no windows, no one else around, no view of the target, and only the hum of the electric motor propelling you towards imminent death.