Kaiten Human Torpedo

The Kaiten (回天, "Heaven Shaker" or "Return to Heaven") was a human torpedo developed by the Imperial Japanese Navy from 1943. It was essentially a modified Type 93 torpedo with an enlarged midsection added to accommodate a single pilot. The Type 1 Kaiten measured 14.75 meters in length and 1 meter in diameter, with a 1,550 kg explosive warhead. It could travel at up to 30 knots, with a maximum range of approximately 78 kilometers at lower speed.

Kaiten were launched from specially modified submarines. The pilot entered the weapon underwater via a connecting tube from the parent submarine, then steered toward the target. An escape hatch existed in theory but was rarely if ever used in practice.

The first operational use of Kaiten came on November 20, 1944, when the Kikusui group attacked US ships at Ulithi Atoll, sinking the oiler USS Mississinewa. Subsequent missions claimed varying results against Allied shipping. In total, about 420 Kaiten were built. Some 106 Kaiten pilots lost their lives, a figure that includes 15 killed in training accidents and two who took their own lives after the surrender; in addition, 846 men died aboard the eight Kaiten-carrying submarines that were sunk.

The first and principal training base was established on Otsushima Island (大津島) in Yamaguchi Prefecture. Further bases followed at Hikari and Hirao, also in Yamaguchi Prefecture, and at Ōga (大神) in the town of Hiji, Oita Prefecture — a shore base on Beppu Bay, not an island.