Kaiten Class, Japanese Manned Suicide Torpedoes

Naval Historical Center #NH 81489

Type 1 Kaiten ("Heaven Shaker")

Specifications:

The Kaiten ("Heaven Shakers") were manned torpedoes intended for suicide attack. 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."

The design was based on the Model 3 Long Lance torpedo. The warhead was removed from the Type 93 and the remainder of the torpedo was joined to a 3.3' (1m) tube with a streamlined fairing. The  main tube had a seat and control panel for the suicide pilot, a simple periscope, and upper and lower hatches. The forward part of the main tube held a second Type 93 oxygen flask and air bottles for the control surfaces, which were enlarged over those of the Type 93. The warhead was 3410 lb (1550 kg) of explosive, with both an inertial pistol and an electrical pistol controlled by the pilot.

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 craft were 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. Even at nominal operating depth, 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 periscope was almost useless at speeds above 5 knots, so a fuel reduction valve was installed to allow the pilot to periodically reduce speed and get a new bearing on his target. The pilot had to maintain trim using a manual water ballast control as his fuel was used up, burdening him with yet another tricky task.

A Kaiten attack was typically launched from about 7000 yards (6500 m) from the target, after the mother submarine had telephoned final instructions to the pilot. An autopilot on the Kaiten was set to steer the craft on the desired compass bearing to a distance about 1100 yards (1000 m) short of the target. At this point the autopilot brought the Kaiten to the surface, allowing the pilot to find his target, adjust his bearing and depth, and make his final approach.

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, I-58, 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.

Photo Gallery

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References

Branfill-Cook (2014)

Campbell (1985)

Carpenter and Polmar (1986)
Frank (1999)
Hastings (2007)

Jentschura, Jung, and Mickel (1977)

Morison (1959)

Yutaka (1962)

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