They were launched into combat from submarines that had been specially adapted to carry this bizarre and fatal cargo. There was a tube which connected the sub to the torpedo – just big enough for the pilot to squeeze through and enter the body of the torpedo. The Kaiten would then fire off in the direction of the target, surface briefly so the pilot could verify his position through a periscope, and then surge on for the final assault. If he missed the target more than once, there was a last resort: self-detonation. Whether the mission was a failure or a success, the pilot would not come back alive.

The first deployments took place in November 1944. One of these Kaiten contained one of the two men who pioneered the creation of these new weapons, and he carried the ashes of his co-inventor, who'd been killed during early testing exercises. This first Kaiten onslaught claimed the USS Mississinewa, which was anchored when the human-torpedo struck. Engulfed in flames, the ship sank with the loss of 63 American sailors, and was a success for the Kaiten fleet – although the Japanese thought they'd actually claimed more targets than they really did.