| Kaiten | |
|---|---|
Kaiten Type 1, Tokyo Yasukuni War Memorial Museum |
|
| Type | Human torpedo |
| Place of origin | Empire of Japan |
| Service history | |
| In service | 1944-1945 |
| Used by | Imperial Japanese Navy |
| Wars | World War II |
| Production history | |
| Number built | approx. 420 |
| Variants | Type 1 Type 1 Mod.1 Type 1 Mod.2 Type 2 (4~ produced) Type 3 (only a project) Type 4 (approx. 50 produced) Type 5 (only a project) Type 6 (only a project) Type 10 (1+2 or 1+6 produced) |
| Specifications | |
|
|
|
| Guidance system |
Manually piloted with gyroscopic stabilisation and automatic running. |
| Launch platform |
Submarine, Surface ship, Coastal bunker |
The Kaiten (Japanese: 回天, literal translation: "Return to the sky", commonly rendered as: "The turn toward heaven", "The Heaven Shaker" or "Change the World"[1]) were manned torpedos and suicide craft, they were used by the Imperial Japanese Navy in the final stages of World War II.
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Towards the end of 1943 the Japanese command in response to unfavorable progress in the war heard suggestions for various suicide craft. These suggestions were initially rejected but later deemed necessary.[2] For the naval department this meant kamikaze planes, suicide boats, submarines and human mines. The kamikazes were somewhat successful, and the second most successful of these were the kaitens.[3]
Research on the first kaitens began in February 1944, followed on July 25 of the same year by the first prototype. By August 1, an order for 100 units had been placed.[4]
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 chamber and 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 linked up to give the pilot full control over the weapon.
The original designers and testers of this new weapon were Lieutenant Hiroshi Kuroki and Lieutenant Sekio Nishina. They were both to die at the controls of kaitens, Lieutenant Kuroki being in a very early training prototype.[5][6][7][8]
In total six models of kaiten were designed, the types 1, 2, 4, 5 and 6 were based on the Type 93 torpedo. The 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.[2]
Early designs allowed the pilot to escape after the final acceleration toward the target. There is no record of any pilot attempting to escape or intending to do so and this provision was dropped from later kaitens so that, once inside, the pilot could not let himself out. The kaiten was fitted with a control for self destruction, intended for use if an attack failed or the impact fuse failed.[9][10]
Kaiten pilots were all men aged between 18 and 20. In the event of their being killed in action their families were promised to be paid ¥10000 reward. It is thought that because of the wartime economy and political climate there was often little choice but to volunteer for Kaiten (or other suicide) duty.
The island of Otsushima, situated in the Inland Sea was used as a training site. It was equipped with cranes and torpedo testing pits, launching ramps as well as a large shallow bay for test running and firing. The Kaiten Memorial Museum is now situated in that location.[11]
Initial readiness training consisted of piloting 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 chamber, 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 treacherous runs around rocks and through channels in deeper waters. The more difficult runs required the pilot to surface and check the periscope multiple times and also required conscious adjusting of trim tank levels because of the reducing weight as oxygen was used up. When the instructors were confident of the pilot's abilities, he would be advanced onto training in open waters against target ships. Training now was often done at full charging speed and in the dark or twilight. The final phase of training would be a submarine launch and more open water running at target ships.[2][12]
Training was dangerous and 15 men died because of accidents, the most common being an accidental impact upon the target vessel. Although the warheads were only dummies, the impact at ramming speed was enough to not only cripple the kaiten but also severely injure the pilot.[13]
In action the kaiten was always piloted by a single person. However in training the larger models (types 2, 4 and 5) could carry two or even four personnel.
Kaiten pilots who were departing for their final missions would leave testaments and messages behind for their loved ones.[14]
Kaiten were designed to be launched from the deck of a submarine or surface ship, or from coastal installations as a coastal defence weapon. The only surface ship recorded as equipped to launch Kaitens was the cruiser Kitakami, which took part in sea launch trials of Type–1 Kaitens.[15][16] In practice, only the Type–1 craft, using the submarine delivery method, were ever used in combat. Specially equipped submarines carried two to six Kaitens, depending on their class. The Kaitens were lashed to the host vessel on wooden blocks with a narrow access tube connected from the submarine to the lower hatch of the Kaiten. This allowed the Kaiten crews to enter from the host submarine while submerged.
Kaitens 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 damaging several others.[11]
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 running 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 set 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 his 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.[2]
Of the six different type classes created, only four were ever significant enough to be noted by the American technological missions into post-war Japan.
Only the type 1, a one-person model with a 1,550 kg (3,400 lb) warhead, was used operationally. Over 300 were built, more than 100 of which were sent on suicide missions.[2][17]
The type 93 torpedo formed the majority of this model of kaiten with the only alterations being the warhead yield being increased from 490 kg (1,100 lb) and the control planes enlarged and altered to allow both gyroscope and pilot control. Between the torpedo's warhead and the engine section is placed the torpedo air flask, 6 (or 8 in later builds) steering air bottles and the forward trim tank followed by the control area and the pilot's seat. In later builds the 5.5 l (9.7 imp pt) 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 the joint protected by a sheet metal cowling.
The pilot's chamber 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 and controls to arm and detonate the weapon if the attack failed, steering, velocity and depth controls were also included. Under the pilot's seat were the batteries for the 20 000 RPM gyroscope.
The air was kept clean by the use of sodium peroxide stored in the pilot's chamber.
The type 6 kaiten was a type 1 with a modified forward air vessel.
After initial water run testing it was decided to have a maximum surface cruising speed and for technical reasons a minimum running speed at any depth of 9.5 km/h (5.1 kn) and a submerged running trim of 1-3° nose-down.
During development and use several problems were encountered, the most pressing being 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.
[2][17] In late 1944 type 2 prototypes were tested in dry-dock and in controlled submerged conditions, however they never met a standard that was satisfactory for open water running.
The type 2 was fueled by diesel and oxidized by the product of the reaction between hydrogen peroxide and hydrazine hydrate catalyzed by potassium cuprocyanide, it also used water as diluent in the combustion cycle. The engine was a bespoke design specifically created to satisfy the requirements for the kaiten. It was of a U8 configuration and was in the aft compartment of the vessel, this compartment was open to the sea and sea-water was used as coolant. The complete operation of the engine had to be simple for a pilot who was already under immense stress so it was designed to be controlled with a single lever.
The general construction of the type 2 is substantially different than that of the type 1. In the forward part of the vessel is the warhead followed by the fuel, trimming and 2 steering air tanks. The forward part of the mid section is occupied by the large complex hydrogen peroxide chamber. This is a 2,600 l (570 imp gal) cylindrical tank that, because of the material it was carrying, was immensely complicated to make. Its construction consisted of welding 5 ribs evenly spaced around the tank, then coating the inside of the tank with tin, then asphalt and finally with a thick tin plating. Construction of each tank took on average 2 weeks and the skill set required was very high.
Following on from the peroxide chamber is the pilot's chamber. This is a much more complex chamber with more controls than in the type 1. From fore to aft controls available to the pilot are: Depth control gear, trim tank controls, electric switches, gyroscope, rudder control, engine control lever, gauges for various attributes, warhead safety gear, engine starter and fuel flow control and lights with their respective switches.
In the aft quarter of the vessel are found the battery for the gyroscope and other electrics, the aft trim tanks and 2 hydrazine hydrate containers. These containers are steel, lined with a rubber bag to prevent sea water (which is used to force the hydrazine hydrate to the engine) and the hydrazine hydrate from coming into contact with each other. Immediately behind these tanks is an auxiliary water tank then the engine compartment.
The engine compartment is always completely filled with sea-water, so it only has mechanical components. Immediately after the midsection is the generator, then the engine, followed by the reduction gears and finally the propeller and control planes.
The type 2 had several improvements over the type 1. It could stay relatively reliably on course with no pilot input and could withstand depths twice as deep as that of the type 1.
Many problems were encountered in the design and engineering of the type 2, mostly relating to the engine. In initial tests water pressure caused deformation and seizing of the engine; although strengthening was added the problem was never fully resolved. Once the engine was installed into a prototype type 2 it was unable to reach the required power rating and this, along with the complexity of the manufacturing process of the type 2 itself, led to the abandonment of the project.
[2][17] In early 1945, concerned with the slow pace of development and the unreliability of the supply of hydrogen peroxide, the Japanese admiralty decided to pursue another line of kaiten development. Engineers responsible for kaiten development were opposed to any new work and wished to expend their efforts on development and production of the type 1.
In all about fifty type 4 prototypes were made, however they never went into full-scale production and were ultimately abandoned.
The type 4 was an attempt to modify the kaiten type 2 to be fuelled by the same kerosene and oxygen combination as the type 93, model 3 torpedo. The dimensions, equipment and engine were all identical to the type 2 although the arrangement differed in several key areas.
The warhead is identical to the type 2, although some later models had an access cover at the after end of the warhead.
The forward end of the forward section contains the air vessels, there are four in this section, one type 93 torpedo air vessel flanked either side by 2 small trim tanks on the keel and three smaller vessels directly above it. The vessels are held in place simply with wood packing. The smaller air vessels are a proprietary design that took some heavy research to perfect. They are sealed by the pressure of the gas, as the pressure rises, a slackly threaded cap presses up against a sealing ring which is screwed down with another cap, thus making an airtight seal. Directly aft of the air vessels is the fuel tank which is ringed by the main forward trim tanks. The fuel tank is lightly constructed and contains baffles to prevent sloshing. Just behind this are the 4 steering air bottles.
The pilots space is identical to that of the type 2 (minus hydrogen peroxide specific circuit controls). Immediately behind the pilot are three more of the smaller oxygen cylinders however in some models these are omitted and chairs are placed for training purposes. Between the bulkheads joining this section with the engine section are two type 93 generators, feeding the same type 6 engine as in the type 2 kaiten.
The type 5 kaiten was a type 4 with a modified forward air vessels.
The first unmanned test runs of the type 4 at cruising speed were made in early 1945, and it was noted that oxygen efficiency was very low. The same problem occurred in the first test run with a pilot, with sensor readings indicating a large percentage of unburned oxygen in the exhaust gasses.
The weapon made little progress in development and never exceeded a speed of 40 km/h in open sea trials; this combined with untraceable leaks in the engine and the consequent inefficiency of the propulsion system led to this design being filed as a failure and its eventual abandonment. The fact that by now the Kaiten Type 1 was in mass production was also a factor in the cancellation of the Type 4.
[2][17] The abandonment of the types 2, 4 and their intermediaries, development of higher capacity batteries, abundance of type 92 torpedoes and the ever increasing urgency to be able to defend the Japanese mainland led to a change of methodology for the kaiten design teams. The type 10 is the result. It is essentially a type 92 electric torpedo with a pilot chamber in-between the warhead and drive unit.
Over 500 units were ordered to be produced between August and October 1945 however, only around 6 (including prototypes) were ever completed.
The type 10 is significantly smaller than the type 1 and consequently has a much smaller warhead of 300 kg (660 lb). The forward section of the weapon contains the warhead and the manual electric fuze, but no contact detonator unlike other kaiten types. The mid section contains the first set of type 92 batteries as well as a steering air bottle strapped to the underneath of the weapon. The pilot's chamber contains firing, starting and gyroscope starting switches as well as a fixed periscope that could only be rotated but not raised or lowered, the rudder control, trim gauge and a sodium peroxide tin for air purification. The latter part of the weapon contained the remainder of the batteries and a small external steering air bottle. The control planes are identical to the type 92 torpedo's other than having a manually operated rudder fitted.
Unlike all previous kaitens the type 10 only had an upper hatch, so could not be entered from within a host submarine. This reflects the design and operation purpose of the weapon as a land-launched coastal defense weapon.
On paper this model had several advantages over the previous types. Firstly it was very simple to construct and maintain. Because it had no pilot controls other than to start and steer it was not complicated to train pilots to use it. It was powered by electricity and consequently had no issue of weight reduction as the fuel was used up, a problem that had caused headaches for test pilots and combat pilots of all previous models. Unlike other models the engine of the type 10 could be stopped and even reversed, although this would be of little practical value in a combat situation. Finally it was very light and small, so it was easily transported to different bases of operation should the need arise.[18]
In practice however, the type 10 proved to be troublesome. Water leaks into the battery compartments and pilot's chamber were commonly reported by test pilots. It was also very cramped and uncomfortable for the pilot. The war ended before development could really iron out these problems so the type never went into mass production.
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 the 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.[18]
When compared with the type 93 torpedo which was surface vessel launched, kaitens had the obvious advantages of having a pilot to guide the weapon, and being launched from a submerged submarine. Despite these advantages, however, they were not nearly as effective round-for-round as the highly successful type 93 torpedo on which they were based. Sources from the United States claim the only sinkings achieved by kaiten attacks were the fleet oiler USS Mississinewa on 20 November 1944 with the loss of 63 men,[19] a small infantry landing craft (LCI-600) with the loss of 3 men[20] and the destroyer escort USS Underhill on 24 July 1945 with the loss of 113 personnel.[21] 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 listen for the impact of their weapons, also the size of the explosion after the attack on the USS Mississinewa gave the impression of a much larger number of ships sunk.
American losses accredited 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 2 suicides after the war). In addition to the pilots, 846 men died as eight Japanese submarines carrying kaiten were sunk and 156 maintenance and support personnel were also killed.[11][22]
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, I-47 and I-36, carrying a total of eight Kaiten.
This mission gave the Kaitens their first sinking, the USS 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.[23][24]
At the same time, the submarine I-37 was spotted and engaged by US ships off of Leyte Island. The boat, together with her Kaitens, was sunk by hedgehog attack from the destroyers USS Conklin and USS McCoy Reynolds, resulting in the loss of 117 officers and men.[22]
The Kongō group (金剛隊) of kaitens was undertaken on 9 January 1945 against the U.S. anchorage at Hollandia, Ulithi, Manus and Kossol Roads.
I-47 launched a further four kaitens and succeeded in only damaging the SS Pontus H Ross, a small "Liberty ship".[23][25]
At Ulithi I-48 was sunk by USS Conklin. None of the 122 men aboard survived.[22]
I-36 engaged US ships with kaitens at Ulithi on 12 January 1945. One of her kaitens was destroyed by depth charge fire from VPB-21 but her other kaitens succeeded in damaging USS Mazama (With 8 fatalities) and sinking an infantry landing craft (USS LCI(L)-600) (With 3 deaths).[20]
I-53 succeeded in launching her four kaitens but only 2 traveled any distance and none reached their targets.
I-58 launched all four kaiten of which one exploded immediately after departure, some time after their launch pillars of smoke are spotted in the distance along their general bearing.
I-56 failed to even reach the launching areas for her kaitens and returned home without firing a single shot.[24][26]
The Chihaya group (千早隊) departed on 20 February 1945 headed for Iwo Jima.
I-44 is spotted and chased for over 2 days underwater running; her carbon dioxide percentage reached 6% before she could escape.
I-368 on approach to Iwo Jima is detected by a Grumman TBF Avenger on 26 February and later attacked with Mark 24 Mines and sunk with the loss of all 85 hands.[22]
I-370 is detected and attacked by USS Finnegan on 26 February. After an initial hedgehog and depth charge run a final depth charge run is commenced and shortly after small explosions and bubbles are detected. I-370 was lost with all 84 officers and men aboard as well as all of her kaitens and pilots.[22][24]
The Shimbu group (神武隊) was originally intended to supplement the previous attacks on Iwo Jima and launched on 1 March 1945. I-58 and I-36 were within a day of Iwo Jima when they were recalled for a new operation. Both returned home safely.[24]
The Tatara group (多々良隊) consisted of I-44, I-47, I-56 and I-58 was to attack the US anchorage at Okinawa, they departed on 28 March 1945.
On 29 March I-47 is attacked by a squadron of Grumman TBF Avengers and is forced to dive. She is pursued for several hours before having to surface once again. On her surfacing she is hit by some shrapnel or fragments and her periscope and fuel tanks are damaged. She is forced to limp home for repairs.[23]
I-56 is detected on approach to Okinawa and hunted by the cruiser USS Bataan and destroyers USS Heermann, USS Uhlmann, USS Collett, USS McCord and USS Mertz she is depth charged heavily by aircraft from the cruiser and the latter three destroyers and eventually succumbs to the ferocity of the assault going down with all 122 persons aboard.[22]
I-58 is hounded by aircraft and anti-submarine fire and arrives to her destination late. She returns without firing a shot.
I-44s location and actions are unknown for the entirety of the mission. A submarine that is likely to be I-44 was attacked around the vicinity of Okinawa on 29 April by an aircraft from the USS Tulagi. The submarine was hit firstly by a depth charge and finally by a mark 24 mine. All 129 hands were lost.[24]
The Tembu group (天武隊) consisted of I-47 and I-36. They were to attack cargo and troop ships between Ulithi and Okinawa. I-47 departs on 20 April and I-36 on 22 April.
On the 27 April I-36 launches her kaitens (four) at a convoy of 28 US ships, none of them are successful in reaching any targets. Two of her kaitens are unable to be launched. I-36 while cruising east of Okinawa notices a replenishment vessel sailing unescorted. The commander attempts to launch kaitens, but they fail, a torpedo attack ends when the torpedoes detonate prematurely.
On 2 May I-47 launches a two kaiten attack upon two US ships, an hour later explosions are heard and I-47 launches one kaiten at the escort vessel. Later analysis shows that none of the kaitens launched were successful and the explosions heard were probably kaiten pilots self destructing or anti-submarine fire.[22][24]
The Shimbu group (振武隊) consisted solely of I-367 and was commenced on 5 May 1945 heading for north-west Saipan, she is damaged by a mine on the 6 May and cannot continue her mission until 17 May. By 27 May I-367 spots a four ship logistics support convoy and launches two kaitens. At least one of the kaitens is destroyed by gun fire from USS Sioux. The rest of the kaitens suffer from failures of some kind and are unable to be launched. I-367 returns home.[24]
The Todoroki group (轟隊) of kaiten equipped submarines sorties on 24 May to patrol east of Guam.
I-36 spots a lone oiler on the 22 June and commences an attack with her kaitens, they both fail and she launches an attack with four conventional torpedoes which explode early and damage the USS Endymion a landing craft repair ship. On the 28 June I-36 attacks the USS Antares with a single kaiten, the ship manages to sink the kaiten with its defensive guns and signals to a nearby destroyer (USS Sproston). The destroyer arrives and begins to attack with depth charges, the submarine launches one of its faulty kaitens controlled manually by its pilot, although it doesn't hit it does help secure the safety of its host submarine. Further ships arrive to the area and they proceed to hunt the I-36, however she manages to escape with only a minor leak in the forward torpedo room and a damaged rudder. She would not see any more action in the war and surrendered to the allies after the official surrender was announced.[27]
On the 16 June I-165 is spotted by USS Devilfish, the US submarine fires a pair of torpedoes but they easily glide by the Japanese vessel. On the 27 June a patrolling Lockheed Ventura spots the I-165 and drops three mark 47 depth charges and successfully hits and sinks the submarine. There were 106 officers and men aboard.[22]
I-361 is detected by a minesweeper on 26 May and the carrier USS Anzio is alerted and launches aircraft to search for the submarine. Five days later a patrolling Grumman TBF Avenger detects the I-361 and launches a volley of rocket fire. The submarine dives and the aircraft drops a mark 24 mine which detonates close to the submarine. The explosion is felt by the crew of USS Oliver Mitchell 30 km (16 nmi) away. All 81 crew were lost.[22]
On the 28 May I-363 spots several ships but is unable to get into kaiten firing range. On the 15 June she spots a convoy and attacks with conventional torpedoes because of rough seas. I-363 returns home.[24]
The Tamon group (多聞隊) is the last kaiten equipped group to go into combat. It was a large force consisting of I-47, I-53, I-58, I-363, I-366 and I-367. They departed on 14 July headed for an area south-east of Okinawa. I-363 and I-367 never engage in further battles before the announcement of unconditional surrender and an end to all hostilities.
The I-47 launches a kaiten at a lone merchant on the 21 July but the attack doesn't succeed. She would see no further action.[24]
Arguably the most successful attack by kaitens was that on the USS Underhill commenced on 24 July 1945. She was a unit of the numerous Buckley class and at the time of sinking was escorting several supply and troop ships. Subsequent to being spotted by a Japanese naval reconnaissance plane; submarine I-53 attached to the Tamon group and carrying six kaitens was redirected to the expected location of the convoy.
The submarine launched a decoy mine ahead of the convoy's position causing the convoy to shift bearing to avoid the mine. This, however, was just diversionary and the mine was a dummy. The USS Underhill after realizing this noticed several sonar contacts, which were later revealed to be a Japanese submarine and several kaitens. A depth charge run was made which did not succeed in killing the submarine although it is suspected that it did succeed in neutralizing one of the kaitens. The depth charge run was followed by a ramming attempt on a submarine at periscope depth.
As the Underhill rammed the surfaced vessel (later revealed to be a kaiten) it was struck by a second kaiten waiting in ambush. Both pilots detonated their charges, one of which led to the detonation of the destroyer's boilers, which led to the her being torn in half by the explosions. The sinking resulted in the loss of almost half of her complement including most of the officers.
One of the attacking kaitens did also attempt an attack on a cargo vessel LST-991, but for some reason glided cleanly under the ship's keel. This very same kaiten could be the one which successfully rammed and sank the Underhill.[21][28]
Yutaka Yokota, a kaiten pilot whose three missions had been canceled due to damage to his weapon or faults with the weapon, was a witness to the attack on Underhill.[11]
Following the successful attack on the Underhill, I-53 launched a further kaiten at an unnamed vessel 6 days later. The attack was unsuccessful. On August 3, I-53 was detected by USS Earl V. Johnson 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.
The I-58 was patrolling the Guam-Leyte route on July 28 when she was forced to dive by an aircraft. A tanker and the USS Lowry were spotted and the commander decided to attack. Two kaitens were launched but one was sunk by gun fire and the other when the destroyer rammed it, although the destroyer was lightly damaged in the process. A day later the I-58 spotted the USS Indianapolis and resolved to make an attacking run; the commander ordered 2 kaitens prepared for attack. Once in firing range the commander realized that 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 August 9 the I-58 noticed a convoy led by the USS Salamaua and readied three of her kaitens to attack, although two failed. One kaiten was launched followed by another heading towards the USS Johnnie Hutchins. One narrowly missed the destroyer, however both were destroyed by gun and depth charge fire. The convoy hunted for further submarines but the I-58 escaped. On August 12 a kaiten attack was made on the USS Oak Hill and her escort the USS Thomas F. Nickel, 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-58's weapons were accounted for, but with two failures, perhaps one was repaired and launched.[29]
On the eleventh of August, I-366 spotted and attacked a convoy north of Palau. The commander attempted to launch all of his kaitens, however two of them failed to launch and the ones that were launched never recorded a hit or even exploded. Less than a week later, Japan surrendered and all submarines were ordered home, thus the I-366 never saw any further action.
The Shinshū group (神州隊) consisted solely of I-159 made way for the Sea of Japan on 16 August 1945. Her duty was to attack Russian convoys. The mission was cancelled by headquarters before any weapons could be fired and I-159 with all of her Kaiten returned home on 18 August 1945.
Japanese naval vessels converted to a Kaiten mother ship were as follows;
Although there are very few intact kaitens left, there are some that have been restored and form part of various exhibits around the world.