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Kaiten

Kaiten

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Encyclopedia
The Kaiten
were manned torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

s and suicide craft
Suicide attack
A suicide attack is a type of attack in which the attacker expects or intends to die in the process.- Historical :...

, they were used by the Imperial Japanese Navy
Imperial Japanese Navy
The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...

 in the final stages of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

History


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.
For the naval department this meant kamikaze
Kamikaze
The were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, designed to destroy as many warships as possible....

 planes, suicide boats, submarines and human mines
Fukuryu
Suicide divers were a part of the Japanese Special Attack Units prepared to resist the invasion of the Home islands by Allied forces. They were armed with a mine containing of explosive, fitted to a bamboo pole. They would dive and stick the pole into the hull of an enemy ship, destroying...

. The kamikazes were somewhat successful, and the second most successful of these were the kaitens.

Research on the first kaitens began in February 1944, followed on July 25 of the same year by the first prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

. By August 1, an order for 100 units had been placed.

Development


The very first kaiten was nothing much more than a Type 93 torpedo
Type 93 torpedo
The Type 93 was a -diameter torpedo of the Imperial Japanese Navy , launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given it after the war by Samuel E. Morison, the chief historian of the U.S...

 engine compartment attached to a cylinder that would become the pilot's chamber and trimming ballast
Ballast tank
A ballast tank is a compartment within a boat, ship or other floating structure that holds water.-History:The basic concept behind the ballast tank can be seen in many forms of aquatic life, such as the blowfish or argonaut octopus, and the concept has been invented and reinvented many times by...

 in place of the warhead
Warhead
The term warhead refers to the explosive material and detonator that is delivered by a missile, rocket, or torpedo.- Etymology :During the early development of naval torpedoes, they could be equipped with an inert payload that was intended for use during training, test firing and exercises. This...

 and other electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 and hydraulics
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...

. The torpedo's pneumatic
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

 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.

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
Type 92 torpedo
The Type 92 torpedo was a submarine-launched torpedo used by the Imperial Japanese Navy during World War II. It was in length and 21 inches in diameter. This type of torpedo was battery powered. It could deliver a 660 pound warhead at 30 knots to a target 7 kilometers away....

. Types 2, 4, 5, 6 and 10 were only manufactured as prototypes and never used in combat.

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.

Pilots


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 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.

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.

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.

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.

Deployment


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
Cruiser
A cruiser is a type of warship. The term has been in use for several hundreds of years, and has had different meanings throughout this period...

 Kitakami
Japanese cruiser Kitakami
was a Kuma class cruiser in the Imperial Japanese Navy, named after the Kitakami River in Iwate Prefecture, Japan.-Background:Kitakami was the third of five vessels completed in the Kuma-class of light cruisers...

, which took part in sea launch trials of Type–1 Kaitens.
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.

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.

Types


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.

Type 1


Only the type 1, a one-person model with a 1550 kg (3,417.2 lb) warhead, was used operationally. Over 300 were built, more than 100 of which were sent on suicide missions.

General arrangement


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 (1,080.3 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
Periscope
A periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle....

 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
Sodium peroxide
Sodium peroxide is the inorganic compound with the formula Na2O2. This solid is the product when sodium is burned with oxygen. It is a strong base and a potent oxidizing agent. It exists in several hydrates and peroxyhydrates including Na2O2·2H2O2·4H2O, Na2O2·2H2O, Na2O2·2H2O2, and...

 stored in the pilot's chamber.

The type 6 kaiten was a type 1 with a modified forward air vessel.

Performance


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 (4.8 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.

Specifications



  • Total weight: 8.3 tonne
  • Length: 14.75 m (48.4 ft)
  • Diameter:: 1 m (3.3 ft)
  • Warhead 1550 kg (3,417.2 lb)
  • Detonation mechanism: Contact, Manual electric fuze
    Fuze
    Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...

  • Engine: Type 93 torpedo engine. Wet heater Double action
    Double-acting cylinder
    A double-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts alternately on both sides of the piston. This is in contrast to a single-acting cylinder, in which the working fluid acts in one direction only....

     Reciprocating
    Reciprocating engine
    A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

     2 cylinder 410 kW
  • Propellant: Kerosene and oxygen
  • Maximum range: 78 km (42.1 nmi)
  • Cruising speed: 22 km/h (11.2 kn)
  • Maximum speed: 56 km/h (28.6 kn)
  • Maximum operating depth: 80 m (262.5 ft)
  • 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 that was satisfactory for open water running.

General arrangement


The type 2 was fueled by diesel and oxidized by the product of the reaction between hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 and hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

 hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....

 catalyzed by potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 cuprocyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

, it also used water as diluent in the combustion cycle. The engine was a bespoke
Bespoke
Bespoke is a term employed in a variety of applications to mean an item custom-made to the buyer's specification...

 design specifically created to satisfy the requirements for the kaiten. It was of a U8
U engine
A U engine is a piston engine made up of two separate straight engines joined by gears or chains. It is similar to the H engine which couples two flat engines...

 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 2600 l (571.9 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.

Performance


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.

Specifications



  • Total weight: 18.37 tonne
  • Length: 16.5 m (54.1 ft)
  • Diameter:: 1.35 m (4.4 ft)
  • Warhead 1500 kg (3,306.9 lb)
  • Detonation mechanism: Contact, Manual electric fuze
    Fuze
    Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...

  • Engine: 4.3 l (262.2 cu in) U8 engine. Wet heater 1110 kW
  • Propellant: Diesel, hydrogen peroxide, hydrazine hydrate and sea water
  • Maximum range: 83 km (44.8 nmi)
  • Maximum speed: 75 km/h (38.3 kn)
  • Maximum operating depth: 100 m (328.1 ft)
  • Number built: 4~ (Yokosuka Naval Arsenal: 1~ produced, Hikari Naval Armory: 3 produced)

Type 4


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.

General arrangement


The type 4 was an attempt to modify the kaiten type 2 to be fuelled by the same kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

 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.

Performance


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.

Specifications

  • Total weight: 18.17 tonne
  • Length: 16.5 m (54.1 ft)
  • Diameter: 1.35 m (4.4 ft)
  • Warhead 1800 kg (3,968.3 lb)
  • Detonation mechanism: Contact, Manual electric fuze
    Fuze
    Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...

  • Engine: 4.3 l (262.2 cu in) U8 engine. Wet heater 900 kW
  • Propellant: Kerosene and oxygen
  • Maximum range: 38 km (20.5 nmi)
  • Maximum speed: 37 km/h (18.9 kn)
  • Maximum operating depth: 100 m (328.1 ft)
  • Number built: approx. 50 produced

Type 10


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.

General arrangement


The type 10 is significantly smaller than the type 1 and consequently has a much smaller warhead of 300 kg (661.4 lb). The forward section of the weapon contains the warhead and the manual electric fuze
Fuze
Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...

, 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.

Performance


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.

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.

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 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.

Specifications



  • Total weight: 3 tonne
  • Length: 9 m (29.5 ft)
  • Diameter: 0.7 m (2.3 ft)
  • Warhead 300 kg (661.4 lb)
  • Detonation mechanism: Manual electric fuze
    Fuze
    Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...

  • Engine: Electric motor 6 kW
  • Propellant: 112 (28×4) battery cells producing 54V at 120A
  • Maximum range: 3.5 km (1.9 nmi)
  • Maximum speed: 13 km/h (6.6 kn)
  • Maximum operating depth: 20 m (65.6 ft)
  • Number built: 1 prototype and 2 or 6 produced

Effectiveness


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
Replenishment Oiler
A replenishment oiler or fleet tanker is a naval auxiliary ship with fuel tanks and dry cargo holds, which can replenish other ships while underway in the high seas. Such ships are used by several countries around the world....

  on 20 November 1944 with the loss of 63 men,
a small infantry landing craft (LCI-600) with the loss of 3 men
and the destroyer escort
Destroyer escort
A destroyer escort is the classification for a smaller, lightly armed warship designed to be used to escort convoys of merchant marine ships, primarily of the United States Merchant Marine in World War II. It is employed primarily for anti-submarine warfare, but also provides some protection...

  on 24 July 1945 with the loss of 113 personnel.
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.

The first deployment


The of kaitens was launched against hostile vessels near Ulithi
Ulithi
Ulithi is an atoll in the Caroline Islands of the western Pacific Ocean, about 191 km east of Yap. It consists of 40 islets totalling , surrounding a lagoon about long and up to wide—at one of the largest in the world. It is administered by the state of Yap in the Federated States of...

 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
USS Mississinewa
USS Mississinewa may refer to:, a Cimarron-class fleet oiler, was launched 28 March 1944 and sunk 15 November 1944, a Neosho-class fleet oiler, was in service from 1955 to 1991...

, 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, the submarine I-37 was spotted and engaged by US ships off of Leyte Island
Leyte Island
Leyte is an island in the Visayas group of the Philippines.The island measures about 180 km north-south and about 65 km at its widest point. In the north it nearly joins Samar, separated by the San Juanico Strait, which becomes as narrow as 2 km in some places...

. The boat, together with her Kaitens, was sunk by hedgehog
Hedgehog (weapon)
The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings...

 attack from the destroyers and , resulting in the loss of 117 officers and men.

The second deployment


The of kaitens was undertaken on 9 January 1945 against the U.S. anchorage at Hollandia
Jayapura
Jayapura City is the capital of Papua province, Indonesia, on the island of New Guinea. It is situated on Yos Sudarso Bay . Its approximate population in 2002 was 200,000....

, Ulithi, Manus
Manus Island
Manus Island is part of Manus Province in northern Papua New Guinea and is the largest island of the Admiralty Islands. It is the fifth largest island in Papua New Guinea with an area of 2,100 km², measuring around 100 km × 30 km. According to the 2000 census, Manus Island had a...

 and Kossol Roads
Kossol Roads
Kossol Roads, Palau is a large body of reef-enclosed water north of Babeldaob. During World War II, it was used by the United States Navy as the location of a floating resupply and repair base....

.

I-47 launched a further four kaitens and succeeded in only damaging the , a small "Liberty ship
Liberty ship
Liberty ships were cargo ships built in the United States during World War II. Though British in conception, they were adapted by the U.S. as they were cheap and quick to build, and came to symbolize U.S. wartime industrial output. Based on vessels ordered by Britain to replace ships torpedoed by...

".

At Ulithi I-48 was sunk by . None of the 122 men aboard survived.

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 (With 8 fatalities) and sinking an infantry landing craft (USS LCI(L)-600)
Landing Craft Infantry
The Landing craft, Infantry or LCI were several classes of sea-going amphibious assault ships of the Second World War utilized to land large numbers of infantry directly onto beaches. They were developed in response to a British request for a vessel capable of carrying and landing substantially...

 (With 3 deaths).

I-53 succeeded in launching her four kaitens but only 2 traveled any distance and none reached their targets.

I-58
Japanese submarine I-58
I-58 was a Japanese B3 type cruiser submarine that served in the final year of World War II. Modified to carry Kaiten manned torpedoes, she damaged two enemy destroyers with them, but her most significant success was the , sunk with conventional torpedoes on 30 July 1945...

 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.

The third deployment


The departed on 20 February 1945 headed for Iwo Jima
Iwo Jima
Iwo Jima, officially , is an island of the Japanese Volcano Islands chain, which lie south of the Ogasawara Islands and together with them form the Ogasawara Archipelago. The island is located south of mainland Tokyo and administered as part of Ogasawara, one of eight villages of Tokyo...

.

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.

I-370 is detected and attacked by 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.

The fourth deployment


The 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.

The fifth deployment


The 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.

I-56 is detected on approach to Okinawa and hunted by the cruiser and destroyers , , , and 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.

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 . The submarine was hit firstly by a depth charge and finally by a mark 24 mine. All 129 hands were lost.

The sixth deployment


The 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.

The seventh deployment


The consisted solely of I-367 and was commenced on 5 May 1945 heading for north-west Saipan
Saipan
Saipan is the largest island of the United States Commonwealth of the Northern Mariana Islands , a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean with a total area of . The 2000 census population was 62,392...

, 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 . The rest of the kaitens suffer from failures of some kind and are unable to be launched. I-367 returns home.

The eighth deployment


The of kaiten equipped submarines sorties on 24 May to patrol east of Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

.

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 a landing craft repair ship. On the 28 June I-36 attacks the with a single kaiten, the ship manages to sink the kaiten with its defensive guns and signals to a nearby destroyer . 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.

On the 16 June I-165 is spotted by , the US submarine fires a pair of torpedoes but they easily glide by the Japanese vessel. On the 27 June a patrolling Lockheed Ventura
Lockheed Ventura
The Lockheed Ventura was a bomber and patrol aircraft of World War II, used by United States and British Commonwealth forces in several guises...

 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.

I-361 is detected by a minesweeper on 26 May and the carrier 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 30 km (16.2 nmi) away. All 81 crew were lost.

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.

The ninth deployment


The 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.
Sinking of the USS Underhill


For more complete information, please see: Underhill sinking.

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
Buckley class destroyer escort
The Buckley class destroyer escorts were 102 destroyer escorts launched in the United States in 1943 - 1944. They served in World War II as convoy escorts and anti-submarine warfare ships. The lead ship was USS Buckley which was launched on 9 January 1943. The ships had General Electric steam...

 and at the time of sinking was escorting several supply and troop ships. Subsequent to being spotted by a Japanese naval reconnaissance plane
Mitsubishi Ki-46
The Mitsubishi Ki-46 was a twin-engine reconnaissance aircraft used by the Imperial Japanese Army in World War II. Its Army Shiki designation was Type 100 Command Reconnaissance Aircraft ; the Allied nickname was "Dinah"....

; 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.

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.

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 and the destroyer began a series of unsuccessful Hedgehog
Hedgehog (weapon)
The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings...

 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 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 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 and readied three of her kaitens to attack, although two failed. One kaiten was launched followed by another heading towards the . 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 and her escort the , 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.

On the eleventh of August, I-366 spotted and attacked a convoy north of Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...

. 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 tenth deployment


The consisted solely of I-159 made way for the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...

 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.

Kaiten carriers


Japanese naval vessels converted to a Kaiten mother ship were as follows;
  • Light cruiser: Kitakami
    Japanese cruiser Kitakami
    was a Kuma class cruiser in the Imperial Japanese Navy, named after the Kitakami River in Iwate Prefecture, Japan.-Background:Kitakami was the third of five vessels completed in the Kuma-class of light cruisers...

  • Destroyer: Shiokaze
    Japanese destroyer Shiokaze
    was a destroyer, built for the Imperial Japanese Navy immediately following World War I. Advanced for their time, these ships served as first-line destroyers through the 1930s, but were considered obsolescent by the start of the Pacific War.-History:...

    , Namikaze
    Japanese destroyer Namikaze
    was the second ship of the Nokaze sub-class, an improvement to the 1st class destroyers built for the Imperial Japanese Navy following World War I...

    , Hanazuki
    Japanese destroyer Hanazuki
    was an Akizuki-class destroyer of the Imperial Japanese Navy. Her name means " March". In June 1947, Hanazuki was turned over to United States as "DD-934", and was later sunk as target off Gotō Islands, Japan on 3 February 1948....

    , Take, Kiri, Sugi, Maki, Kashi, Kaya
    Japanese destroyer Kaya (Type D)
    Japanese destroyer Kaya was a in service during the later part of World War II....

    , Kaede
    Japanese destroyer Kaede (Type D)
    Kaede was a Japanese in service during the later part of World War II. After the war the ship was ceded to China....

    , Tsuta, Hagi, Nire, Nashi, Shii
  • Submarine: I-36, I-37, I-38, I-41, I-44, I-46, I-47, I-48, I-53, I-56, I-58
    Japanese submarine I-58
    I-58 was a Japanese B3 type cruiser submarine that served in the final year of World War II. Modified to carry Kaiten manned torpedoes, she damaged two enemy destroyers with them, but her most significant success was the , sunk with conventional torpedoes on 30 July 1945...

    , I-156, I-157, I-158, I-159, I-162, I-165, I-361, I-363, I-366, I-367, I-368, I-370, I-372


Exhibits


Although there are very few intact kaitens left, there are some that have been restored and form part of various exhibits around the world.
  • Kure Maritime Museum
    Yamato Museum
    The Yamato Museum is a nickname of the "Kure Maritime Museum" in Kure, Hiroshima, Japan.-History:The museum opened on April 23, 2005. It is nicknamed the Yamato Museum due to the display in the lobby of the large model ship Yamato Hiroba, a 1/10 scale model of the Japanese battleship Yamato...

    , Kure
    Kure
    Kure can refer to:*KURE, a radio station in Ames, Iowa*Kure Software Koubou, Japanese video game development company*Kure, Hiroshima , a city in Hiroshima prefecture, Japan**Kure Line, a rail line in the city...

    , Hiroshima Prefecture
    Hiroshima Prefecture
    is a prefecture of Japan located in the Chūgoku region on Honshu island. The capital is the city of Hiroshima.- History :The area around Hiroshima was formerly divided into Bingo Province and Aki Province. This location has been a center of trade and culture since the beginning of Japan's recorded...

    . A refurbished type 10.
  • History and Folklore Museum, Yamaguchi
    Yamaguchi, Yamaguchi
    is the capital city of Yamaguchi Prefecture, Japan.As of February 1, 2010, the city has an estimated population of 198,971 and a population density of 194.44 persons per km²...

    , Yamaguchi Prefecture
    Yamaguchi Prefecture
    is a prefecture of Japan in the Chūgoku region on Honshū island. The capital is the city of Yamaguchi, in the center of the prefecture. The largest city, however, is Shimonoseki.- History :...

    . A type 2 hull section is displayed in the Word War 2 exhibit.
  • Yasukuni War Memorial Museum, Tokyo. A type 1 and section of hull from a type 4, in the great hall.
  • New Jersey Naval Museum
    New Jersey Naval Museum
    The New Jersey Naval Museum , located along the Hackensack River in Hackensack, New Jersey, is dedicated to New Jersey's Navy heritage and naval history in general. The prominent element in the collection is the USS Ling , a long Balao-class submarine of World War II...

    , Hackensack, New Jersey
    Hackensack, New Jersey
    Hackensack is a city in Bergen County, New Jersey, United States and the county seat of Bergen County. Although informally called Hackensack, it was officially named New Barbadoes Township until 1921. As of the 2010 United States Census, the city population was 43,010....

    , United States
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

    . A preserved type 4.
  • Keyport Naval Submarine Museum, Seattle, Washington
    Seattle, Washington
    Seattle is the county seat of King County, Washington. With 608,660 residents as of the 2010 Census, Seattle is the largest city in the Northwestern United States. The Seattle metropolitan area of about 3.4 million inhabitants is the 15th largest metropolitan area in the country...

    , United States. A sliced open type 1.
  • USS Bowfin museum, Oahu, Hawaii, United States. A preserved type 4 with windows cut into it for visibility.
  • The Royal Navy Submarine Museum, Gosport
    Gosport
    Gosport is a town, district and borough situated on the south coast of England, within the county of Hampshire. It has approximately 80,000 permanent residents with a further 5,000-10,000 during the summer months...

    , United Kingdom
    United Kingdom
    The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

    . A section of a type 4.

Further reading

  • Midget submarine
    Midget submarine
    A midget submarine is any submarine under 150 tons, typically operated by a crew of one or two but sometimes up to 6 or 8, with little or no on-board living accommodation...

  • Human torpedo
    Human torpedo
    Human torpedoes or manned torpedoes are a type of rideable submarine used as secret naval weapons in World War II. The basic design is still in use today; they are a type of diver propulsion vehicle....

  • Living torpedo
  • Type 92 torpedo
    Type 92 torpedo
    The Type 92 torpedo was a submarine-launched torpedo used by the Imperial Japanese Navy during World War II. It was in length and 21 inches in diameter. This type of torpedo was battery powered. It could deliver a 660 pound warhead at 30 knots to a target 7 kilometers away....

  • Type 93 torpedo
    Type 93 torpedo
    The Type 93 was a -diameter torpedo of the Imperial Japanese Navy , launched from surface ships. It is commonly referred to as the Long Lance by most modern English-language naval historians, a nickname given it after the war by Samuel E. Morison, the chief historian of the U.S...

  • Kamikaze
    Kamikaze
    The were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, designed to destroy as many warships as possible....

  • Shinyo
  • Fukuryu
    Fukuryu
    Suicide divers were a part of the Japanese Special Attack Units prepared to resist the invasion of the Home islands by Allied forces. They were armed with a mine containing of explosive, fitted to a bamboo pole. They would dive and stick the pole into the hull of an enemy ship, destroying...

  • Kairyu
    Kairyu class submarine
    The was a class of midget submarines of the Imperial Japanese Navy, designed in 1943–1944, and produced from the beginning of 1945. These submarines were meant to meet the invading American naval forces upon their anticipated approach of Tokyo.-History:...


External links