Kaiten

Cardinal Richelieu

I don't think this topic has ever been covered here. I came across the Kaiten manned torpedo recently in a Japanese War Movie. Like the Kamakazee of the air its actually success was overplayed.

http://pwencycl.kgbudge.com/K/a/Kaiten_class.htm

The Kaiten ("Heaven Shakers") were manned torpedoes intended for suicide attack. They were based on the Model 3 Long Lance torpedo. The design was completed in the spring of 1943, but senior officers initially rejected the concept because there was no way for the pilot to escape. At one point the inventors, Ensign Nishina Sekio and Lieutenant (junior grade) Kuroki Hiroshi, wrote a petition in their own blood begging the high command to reconsider. This was a traditional way in Japanese culture to show one's makoto ("sincerity"). Approval of the prototype design finally was granted in February 1944, on condition that the weapon have an escape mechanism for the pilot, but production remained slow. This changed after the loss of Saipan in June 1944. A crash program was begun to manufacture the weapon and train its crew, under the cover name "Circle Six Metal Fitting."

Although a number of surface ships were modified to carry Kaiten, the only attacks actually launched were from submarines. These were modified with four to six access tubes that allowed the Kaiten crew to man their craft from within the mother submarine. This necessitated removing any deck guns, reducing the mother submarine's defenses. The Kaiten was released about 7000 yards (7000 meters) from the target with its gyroscopes already set by the submarine navigator for the desired course and run time. The Kaiten ran at a depth of 20 feet (6 meters) during its initial run, then surfaced so that the pilot could pick out a target before setting course and diving to a suitable attack depth. If he missed, he was expected to surface and repeat the process. The explosive charge could be triggered either by impact or manually by the pilot.

With their high speed and large explosive charge, Kaiten were potentially quite dangerous. However, the Kaiten had a tendency to suffer leaks into the control compartment while its mother submarine was submerged. This caused about 40 percent of the Kaiten to suffer starting explosions in their waterlogged power units. The controls tended to be heavy and difficult to work, which was only worsened by corrosion damage from seawater. The craft were also only designed to withstand water pressure equivalent to a depth of 250 feet, which limited the dive depth of their mother submarines. A close depth charge attack on the mother submarine almost always disabled any Kaiten on deck.

The Kaiten's first combat mission took place on 18 November 1944. Submarines I-36, I-37, and I-47 were equipped with four Kaiten each, of which two could be manned directly from the mother submarine through access tubes, while the other two had to be manned while the submarine was surfaced. (On later missions, modifications were made so that all the Kaiten could be manned through access tubes.) I-36 and I-47 were assigned to attack Ulithi while I-37 would attack Kossol Roads. I-37 was detected and sunk before it could carry out its attack, and I-36 suffered malfunctions of three of its four Kaiten, but I-47 was able to launch all four. The mother submarines heard several explosions some time after launching their Kaiten, and the Japanese made exaggerated claims of three carriers and two battleships sunk. However, Allied records show that the only casualty was oiler Mississinewa.
Later missions were little more successful. Several mother submarines were sunk before they could launch their attacks, and mechanical or electrical failures meant that over half of those Kaiten that were delivered to their target areas could not be launched. The kaiten unit sent to Iwo Jima, consisting of I-370, I-368, and I-44, lost I-370 to a depth charge attack from destroyer escort Finnegan, while I-368 was sunk by aircraft from escort carrier Anzio. I-44 was pinned down by destroyers for 48 hours, nearly to the point of exhausting its oxygen supply, and was unable to make a successful attack. Many of the attacks against protected anchorages were foiled by antisubmarine nets. As a result, a number of Kaiten crew returned alive from their combat patrols, which was extremely damaging to the morale of men who had prepared themselves for certain death. However, the tendency of the Japanese to claim a kill every time the crew of a mother ship heard a Kaiten explode meant that realistic damage assessments were never made, or at least never published, though a change of strategy from attacking fleet anchorages to attacking convoys suggests that the Navy leadership were aware that their claims were suspect.
The catastrophic losses among Japanese conventional submarines and the threat of invasion dictated yet another change of strategy, to the use of Kaiten as coastal defense craft. These Kaiten would be based in hidden caves or coves near likely landing beaches and launched against the transports bringing in the assault force. The Japanese also began pressing transport submarines, never designed for combat, into service as Kaiten carriers. These lacked range and speed and proved highly vulnerable to Allied antisubmarine defenses.

A Kaiten was responsible for the destruction of destroyer escort Underhill on 24 July 1945. Underhill made a sound contact and rammed the Kaiten, thereby accomplishing its mission for it. The forward half of the destroyer escort was obliterated in a massive explosion that killed 112 of the crew, leaving 116 survivors to be rescued by nearby ships. Some historians suspect that Indianapolis fell victim to a Kaiten rather than conventional torpedo attack, though the commander of the submarine credited with sinking Indianapolis insisted that he used conventional torpedoes rather than his load of Kaiten.
About 1375 crew were assigned to Kaiten, many of whom were volunteers from among the trainee pilots of the Tsuchiura and Nara naval air stations. However, a shortage of the craft meant that only 150 sailors completed the training course, with fifteen deaths during training. Among these was Kuroki, whose ashes were taken by Nishina on the Ulithi mission. In return for sinking Mississinewa, Underhill, and cargo ship Canada Victory, the Japanese expended 80 Kaiten and their crew in combat, another 15 in training accidents, and eight mother submarines with over 600 men.

Models of Kaiten on Submarine. The one man Kaiten crew would enter from the main vessel.

Delancey

The Kaiten's greatest drawback was the need for a ' mother ship ' and many submarines that could have been more effectively used were lost on Kaiten missions having been left badly exposed.
Of course despite having the best torpedoe of any WW2 combatant ( Long Lance ) the Japanese never really utilised thier subs to greatest effect and tended to ' fritter ' them away on re-supply operations.

The sinking of the USS Underhill was significant in the story of the USS Indianapolis , the loss of the Underhill was never notified to the Indianapolis Captain who thus did not steer a zig zag course thus making his ship an easier target . It is debatable however if this would have prevented what was the greatest US Navy loss of life since the Arizona was lost at Pearl Harbour.