Kaiten
Kaiten were crewed torpedoes and suicide craft, used by the Imperial Japanese Navy in the final stages of World War II.
Background
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.
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 Kaiten so that, once inside, the pilot could not unlock the hatches. The Kaiten was fitted with a self-destruct control, intended for use if an attack failed or the impact fuze failed.
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 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
Kaiten were designed to be launched from the deck of a submarine or surface ship, or from coastal installations as a coastal defense weapon. The cruiser Kitakami was equipped to launch eight Kaiten and took part in sea launch trials of Type 1s. In addition, two destroyers of the Minekaze-class were converted to Kaiten carriers. Shiokaze could carry four, and Namikaze two. Twelve destroyers of the Matsu-class were to follow with capacity for one Kaiten, however only one, Take, was completed.In practice, only the Type 1 craft, using the submarine delivery method, were ever used in combat. Twenty-one specially equipped submarines carried two, four, five, or six Kaiten, depending on their class. The Kaiten were lashed to the host vessel on wooden blocks with a narrow access tube connecting the submarine to the lower hatch of the Kaiten. This allowed the Kaiten crew to enter from the host submarine while submerged.
Kaiten had a very limited diving depth, which in turn limited the diving depth of the host submarine. This is one of several factors blamed for the very poor survival rate of submarines using them, eight submarines being lost for the sinking of only two enemy ships and damage to several others.
Once the target was acquired and the host submarine was within range, the pilot was briefed, the Kaiten's starting air bottles were charged, and the cockpit was ventilated. The pilot then entered the vessel, the gyroscope was programmed with the correct bearing and depth and the pilot was given his final briefing.
The Kaiten separated from the host submarine and headed at speed in the direction fed into the gyroscope. Once within final attack range the Kaiten would surface and the pilot would check his range and bearing via periscope and make any adjustments necessary. He would then submerge to a suitable depth, arm the warhead and proceed on his final attack run. If he missed he could make adjustments and try again. If the mission failed he would detonate his vessel as a last resort.
Types
Of the seven type classes created, only four were significant enough to be noted by the American technical missions to post-war Japan.Type 1
Only the Type 1, a one-man model with a 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 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 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
- 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
General arrangement
The Type 2 was fueled by diesel fuel oxidized by the product of the reaction between hydrogen peroxide and hydrazine hydrate catalyzed by potassium cuprocyanide; water was also used as a diluent in the combustion cycle. The engine was a custom design specifically created to satisfy the requirements of the Kaiten. It was of a U8 configuration and was in the aft compartment of the vessel. This compartment was open to the sea, with seawater 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 by 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 midsection is occupied by the hydrogen peroxide chamber. This cylindrical tank required a complicated construction of welding five ribs evenly spaced around the circumference, 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 required was very high.
Behind the peroxide chamber is the pilot's compartment. This is much more complex with more controls than that of 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 applications, warhead safety gear, engine starter, fuel flow control, and lights with their respective switches.
In the aft quarter of the vessel is found the battery for the gyroscope and other electronics, the aft trim tanks and 2 hydrazine hydrate containers. These containers are made of steel lined with a rubber bag to prevent sea water 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, the engine, the reduction gears, and finally the propeller and control planes.