Кайтэны: торпеды-камикадзе Императорского флота Японии

Crewed torpedoes and suicide craft, used by the Imperial Japanese Navy in WWII
the suicide torpedo

Kaiten (回天) were crewed torpedoes and suicide craft, used by the Imperial Japanese Navy in the final stages of World War II.

In recognition of the unfavorable progress of the war, towards the end of 1943 the Japanese high command considered suggestions for various suicide craft. These suggestions were initially rejected, but later deemed necessary. Various suicide craft were developed in the Japanese Special Attack Units. For the Navy, this meant Kamikaze planes, Ohka piloted bombs, Shinyo suicide boats, Kaiten submarines, and Fukuryu suicide divers or human mines. The Kamikazes were somewhat successful, and the second most successful were the Kaitens. Research on the first Kaiten began in February 1944, followed on 25 July of the same year by the first prototype. By 1 August, an order for 100 units had been placed.

The very first Kaiten was nothing much more than a Type 93 torpedo engine compartment attached to a cylinder that would become the pilot's compartment with trimming ballast in place of the warhead and other electronics and hydraulics. The torpedo's pneumatic gyroscope was replaced by an electric model, and controls were installed which gave the pilot full control of the weapon. The original designers and testers of this new weapon were Lieutenant Hiroshi Kuroki and Lieutenant Sekio Nishina. They both died at the controls of Kaiten, Lieutenant Kuroki in a very early training prototype. In total six models of Kaiten were designed, Types 1, 2, 4, 5, and 6 were based on the Type 93 torpedo. Type 10 was the only model based on the Type 92 torpedo. Types 2, 4, 5, 6, and 10 were only manufactured as prototypes and never used in combat.

The island of Ōzushima, in the Inland Sea, was used as a training site. The island was equipped with cranes, torpedo testing pits, launch ramps, and had a large shallow bay for test running and firing. The Kaiten Memorial Museum is now situated there. Kaiten pilots were all men aged between 17 and 28. Initial training consisted of sailing fast surface boats by periscope and instrument readings alone. When a pilot had advanced past this basic training, he would begin training on Kaitens. Training craft were fitted with a dummy warhead that contained telemetry equipment and an emergency blowing tank that could return the craft to the surface should the trainee dive to a dangerous depth. Kaiten training started with basic circular runs to and from a fixed landmark at a reduced speed; the training advanced to faster and more hazardous runs around rocks and through channels in deeper waters. The more difficult runs required the pilot to surface and check the periscope repeatedly, and required conscientious adjusting of trim tank levels because of the reducing weight as oxygen was used up. When the instructors were confident about a pilot's abilities, they would advance the pilot to open water training against target ships. Training at this level was often done at full attack speed, and either at night or in twilight. The final phase of training would be a submarine launch and more open water attack runs on target ships. Training was dangerous, and 15 men died in accidents, most commonly collisions with the target vessels. Although the warheads were only dummies, the impact at ramming speed was enough to both cripple the Kaiten and severely injure the pilot. In action, the Kaiten was always operated by one man, but the larger training models (Types 2, 4, and 5) could carry two or even four. Kaiten pilots who were leaving for their final missions would leave testaments and messages behind for their loved ones.

Kaiten were designed to be launched from the deck of a submarine or surface ship, or from coastal installations as a coastal defense weapon. The cruiser Kitakami was equipped to launch eight Kaiten and took part in sea launch trials of Type 1s. In addition, two destroyers of the Minekaze class were converted to Kaiten carriers. Shiokaze could carry four, and Namikaze two. Twelve destroyers of the Matsu class were to follow with capacity for one Kaiten, however only one, Take, was completed. In practice, only the Type 1 craft, using the submarine delivery method, were ever used in combat. Twenty one specially equipped submarines carried two, four, five, or six Kaiten, depending on their class. The Kaiten were lashed to the host vessel on wooden blocks with a narrow access tube connecting the submarine to the lower hatch of the Kaiten. This allowed the Kaiten crew to enter from the host submarine while submerged. Kaiten had a very limited diving depth, which in turn limited the diving depth of the host submarine. This is one of several factors blamed for the very poor survival rate of submarines using them, eight submarines being lost for the sinking of only two enemy ships and damage to several others. Once the target was acquired and the host submarine was within range the pilot was briefed, the Kaiten's starting air bottles were charged and the cockpit was ventilated. The pilot then entered the vessel, the gyroscope was programmed with the correct bearing and depth and the pilot was given his final briefing. The Kaiten separated from the host submarine and headed at speed in the direction fed into the gyroscope. Once within final attack range the Kaiten would surface and the pilot would check his range and bearing via periscope and make any adjustments necessary. He would then submerge to a suitable depth, arm the warhead and proceed on his final attack run. If he missed he could make adjustments and try again. If the mission failed he would detonate his vessel as a last resort.

The Type 93 torpedo formed the majority of this model of Kaiten with the only alterations being the warhead yield being increased from and the control planes enlarged and altered to allow both gyroscope and pilot control. Between the torpedo warhead and the engine section is the torpedo compressed air flask, 6 (or 8 in later models) steering air bottles and the forward trim tank, followed by the control area and the pilot's seat. In later models the Tetrachloromethane starting air bottle is located in the cockpit and a further smaller trimming tank is supplied for use at initial launch. The engine section is slotted in above the aft trim tank with the joint protected by a sheet metal cowl. The pilot's compartment was entered from below through the lower hatch, which was mated to the host submarine. There was a small hand operated periscope with a vertical range of about 70 cm, controls to arm and detonate the weapon if the attack failed and steering, velocity and depth controls. Batteries to power the 20,000 rpm gyroscope were located under the pilot's seat. The air was filtered by sodium peroxide stored in the pilot's compartment. The Type 6 Kaiten was a Type 1 with a modified forward air tank.

After initial trials in water, it was decided to have a maximum surface cruising speed and, for technical reasons, a minimum running speed at any depth of and a submerged running trim of 1–3° nose down. During development and use several problems were encountered; the most pressing were major water leaks into the pilot's chamber during transport and deep diving, and explosions caused by ingress of water into the torpedo engine. These were never fully eliminated during the weapon's active service.

In late 1944, Type 2 prototypes were tested in dry dock and in controlled submerged conditions; however, they never met a standard satisfactory for open water running.

In practice however, the Type 10 proved to be troublesome. Water leaks into the battery compartments and pilot's compartment were commonly reported by test pilots. It was also very cramped and uncomfortable for the pilot. Japan surrendered before full development could finish.

The Type 10 was designed and intended as a coastal defense weapon to counter the expected invasion of the Japanese mainland by Allied troops. On 16 July 1945 the Imperial Japanese Naval command ordered the construction of over 500 Type 10s to be stationed and readied for launch from several existing and new kaiten bases. Details available in the Deployment section above.

When compared with the Type 93 torpedo which was surface vessel–launched, Kaiten had the obvious advantages of having a pilot to guide the weapon, and of being launched from a submerged submarine. Despite these advantages, however, they were not nearly as effective on a one for one basis as the highly successful Type 93 torpedo on which they were based. United States sources claim that the only sinkings achieved by Kaiten attacks were the fleet oiler Mississinewa anchored at Ulithi on 20 November 1944, with the loss of 63 men; a small infantry landing craft (LCI 600), with the loss of three men; and the destroyer escort Underhill while operating northeast of Cape Engaño on 24 July 1945, with the loss of 113 men. Contrary to the above, some Japanese sources give much larger numbers of Kaiten successes. Reasons given for this discrepancy are the fact that the submarine launching the Kaiten could only estimate success by listening for the detonation of their weapons, and also that the size of the explosion after the attack on USS Mississinewa gave the impression of a much larger number of ships sunk. American losses attributed to Kaiten attacks came to a total of 187 officers and men. The losses of Kaiten crews and support staff were much higher. In total 106 Kaiten pilots lost their lives (including 15 killed in training accidents and two suicides after the war). In addition to the pilots, 846 men died when eight Japanese submarines carrying Kaiten were sunk, and 156 maintenance and support personnel were also killed.

The Kikusui group (菊水隊) of kaitens was launched against hostile vessels near Ulithi on 20 November 1944. The group consisted of two submarines, Japanese submarine I 47 and I 36, carrying a total of eight Kaiten. This mission gave the Kaiten their first sinking, Mississinewa, but at the cost of all eight Kaiten pilots. The first Kaiten launched from I 47 was piloted by Sekio Nishina, one of the original designers of the weapon. He carried with him the ashes of the other creator, Hiroshi Kuroki, who died in a training accident very early in the Kaiten's development. At the same time, submarine I 37 was sighted and engaged by US ships off of Leyte Island. The boat, together with her Kaiten, was sunk by hedgehog attack from the destroyers Conklin and McCoy Reynolds, resulting in the loss of 117 officers and men.

The Kongō group (金剛隊) of Kaiten operation was undertaken on 9 January 1945 against the U. S. anchorage at Hollandia, Ulithi, Manus, Kossol Roads and Apra Harbor. I 36 engaged US ships with Kaiten at Ulithi on 12 January 1945. One was destroyed by depth charges from VPB 21 but the others succeeded in damaging Mazama (with eight casualties) and sinking an infantry landing craft (USS LCI(L) 600) (with three deaths). At Ulithi was sunk by Conklin. None of the 122 men aboard survived. launched all four Kaiten off Apra Harbor, of which one exploded immediately after launch. Sometime after deployment, pillars of smoke were seen in the distance along their general bearing.