Kaiten

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

Background

thumb|left|upright|Kaiten Type 1 periscope at the [[Yūshūkan|Tokyo Yasukuni War Memorial]]

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 as defeatist 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.

Development

The very first Kaiten was little 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.

Pilots

The island of Ōzushima, in the Inland Sea, was used as a training site. The island was equipped with cranes, torpedo testing pits, and 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.

Deployment

thumb|300px|left|Map of known Kaiten base locations at the end of World War II

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 were converted to Kaiten carriers. Namikaze was modified to carry two to four, while 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 using metal bands that could be unlatched with a lever in the cockpit. A narrow access tube connected the submarine to the lower hatch of the Kaiten. This allowed the Kaiten crew to enter from the host submarine while submerged.

thumb|right|A Kaiten Type 1 being trial-launched from the light cruiser Kitakami

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 before the hatches were locked.

The pilot would pull a lever to release the latches that fastened the metal rings holding the Kaiten down, separating it from the host submarine. It then 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.

General arrangement

thumb|upright=1.5|Schematic of a Kaiten type 1

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, while the Type 3 would've had an improved kerosene-oxygen engine, later used in the Type 4.

Performance

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.

Several problems were encountered during development and use; 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.

Specifications

thumb|A Kaiten Type I at the [[Yūshūkan|Tokyo Yasukuni War Memorial Museum]]

Total weight:
Length:
Diameter:
Warhead:
Detonation mechanism: Contact, Manual electric fuze
Engine: Type 93 torpedo engine. Wet heater Double action Reciprocating 2 cylinder
Propellant: Kerosene and oxygen
Maximum range:
Cruising speed:
Maximum speed:
Maximum operating depth:
Number built: approx. 330 produced

Type 2

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.

Type 4

Type 10

In practice, however, the Type 10 proved to be troublesome. Water leakage into the battery and pilot compartments were commonly reported, and it was generally very cramped and uncomfortable for the pilot. Japan surrendered before full development could finish.

Deployment plans

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.

Effectiveness

thumb|, victim of a kaiten attack on 20 November 1944

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 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 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 estimate success only by listening for the detonation, 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.

Deployments

First

The of kaitens was launched against hostile vessels near Ulithi on 20 November 1944. The group consisted of two submarines, and I-36, carrying a total of eight Kaiten.

This mission gave the Kaiten their first sinking, , 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 destroyer escorts and , resulting in the loss of 117 officers and men.

Second

The 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 (with eight casualties) and sinking an infantry landing craft (USS LCI(L)-600) (with three deaths).

At Ulithi was sunk by . 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.

Third

The departed on 20 February 1945 for Iwo Jima.

was sighted and hunted for over two days underwater; crew compartment carbon dioxide saturation reached 6% before she managed to escape.

was detected and attacked by a Grumman TBF Avenger on approaching Iwo Jima on 26 February and was sunk by Mark 24 Mines with the loss of all 85 hands.

On 16 June the US submarine fired two torpedoes at the , both of which missed. On 27 June, a patrolling Lockheed Ventura sighted I-165 and dropped three Mark 47 depth charges which sank her with her crew of 106.

Yutaka Yokota, a Kaiten pilot whose three missions were canceled due to mechanical failures, and who wrote a memoir of his Kaiten experiences, witnessed the attack on the Underhill.

Following the successful attack on the Underhill, I-53 launched a further Kaiten at an unnamed vessel six days later. The attack was unsuccessful. On 3 August I-53 was detected by and the destroyer began a series of unsuccessful Hedgehog attacks. I-53 launched two Kaitens separated by 30 minutes, explosions were heard, and it was confirmed that the destroyer was damaged in the attack. She escaped pursuit and returned home.

I-58 was patrolling the Guam-Leyte route on 28 July when she was forced to dive by an aircraft. A tanker and a destroyer, , were sighted and the commander decided to attack. Two Kaiten were launched, one of which was sunk by gunfire and the other by ramming, damaging the destroyer slightly in the process. A day later, I-58 sighted and the commander, Mochitsura Hashimoto ordered two Kaiten prepared for attack. Once in firing range the commander realised it would be a waste of a Kaiten to attack such an easy target, and instead launched a spread of six Type 95 torpedoes, three of which hit, causing the cruiser to sink rapidly. On 9 August I-58 came across a convoy led by and readied three of her Kaitens to attack, of which only one could be launched. This was followed by another rapidly prepared, and both made for . Although one narrowly missed the destroyer, both were destroyed by gunfire and depth charging. The convoy searched for other submarines, but I-58 escaped. On 12 August a Kaiten was launched against and her escort . The Kaiten passed under the destroyer, then surfaced and self-detonated. A second object was spotted by the destroyer and depth charges were launched, after which an explosion occurred. Whether this was a Kaiten is unknown, as all six of I-58s weapons were accounted for, but with two failures, perhaps one was repaired and launched later.

On 11 August I-366 attacked a convoy north of Palau. The commander attempted to launch all of the Kaiten, but two failed, and the ones that were launched didn't score a hit or even explode. Less than a week later, Japan surrendered and all submarines were ordered home, and I-366 saw no further action.

Tenth

The consisting solely of , sailed on 16 August 1945 to attack Soviet convoys in the Sea of Japan. The mission was cancelled by headquarters before any action and I-159 returned with all of her Kaiten on 18 August 1945.

Kaiten carriers

Japanese naval vessels adapted to carry Kaiten were:

Light cruiser: Kitakami
Destroyer: Namikaze, Take, Kiri, Sugi, Maki, Kashi, Kaya, Kaede, Tsuta, Hagi, Nire, Nashi, Shii
Submarine: I-36, I-37, I-44, I-46, I-47, I-48, I-53, ', I-58, I-156, I-157, I-158, I-159, I-162, I-165, I-361, I-363, I-366, I-367, I-368, I-370

File:Japanese submarine I-47 in 1944.jpg|Submarine I-47 as Kikusui group on 8 November 1944

File:Japanese submarine I-56.jpg|Submarine I-56 as Kongō group on 21 December 1944

File:Japanese submarine I-47.jpg|Submarine I-47 as Kongō group on 25 December 1944

File:Japanese submarine I-48.jpg|Submarine I-48 as Kongō group on 1 January 1945

File:Japanese submarine I-370.jpg|Submarine I-370 as Chihaya group on 21 February 1945

File:Japanese submarine I-44.jpg|Submarine I-44 as Tatara group on 3 April 1945

File:2 kaiten atop C2 submarine.jpg|Submarine I-36 as Tembu group

File:KaitenMission.JPG|Submarine I-47 as Tembu group on 20 April 1945

File:Japanese submarine I-367 in May 1945.jpg|Submarine I-367 as Simbu group on 2 May 1945

File:Japanese submarine I-361.jpg|Submarine I-361 as Todoroki group on 23 May 1945

File:Japanese submarine I-165 in 1945.jpg|Submarine I-165 as Todoroki group on 15 June 1945

File:Japanese submarine I-367.jpg|Submarine I-367 as Tamon group on 19 July 1945

File:Japanese submarine I-363.jpg|Submarine I-363 as Tamon group in August 1945

File:Japanese cruiser Kitakami 1945.jpg|Light cruiser Kitakami on 20 January 1945 at Sasebo Naval Arsenal

File:Kaiten Type 1 launch test from port of Japanese cruiser Kitakami.jpg|Kaiten Type 1 being trial launched from the light cruiser Kitakami (port)

File:Japanese Matsu-class destroyers.jpg|Type D destroyers on 11 September 1945 at Kure Naval Base

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Exhibits

Although most surviving Kaitens were scrapped after World War II, some have survived into preservation, and have been placed on display at museums around the world.

Kure Maritime Museum, Kure, Hiroshima Prefecture. A restored Type 10.
History and Folklore Museum, Yamaguchi, Yamaguchi Prefecture. A Type 2 hull section in the World War II exhibition.
Yasukuni War Memorial Museum, Tokyo. A Type 1 and section of hull from a Type 4, in the main hall.
New Jersey Naval Museum, Hackensack, New Jersey, United States. A preserved Type 4.
United States Naval Undersea Museum, Keyport, Washington, United States. A cut open Type 1.
USS Bowfin Submarine Museum, Oahu, Hawaii, United States. A preserved Type 4 with windows cut into it for inspection.
Explosion! Museum of Naval Firepower, Gosport, United Kingdom. A section of a Type 2.

References

External links

US Navy Historical Center Account of the kaiten program.
Kaitens in action. Details of battles and accounts of kaitens type 1 and 2.
Account from a crewman of Kaiten Special Attack Corps Submarine A-367
Stories and Battle Histories of the IJN's Submarines
HNSA Web Page: IJN Kaiten
Human torpedo 回天 Kaiten (Japanese)
Development and history. Information about kaitens, their history, crews, bases, and technical information. (Japanese).