Speaker: Tadamasa Iwai
Former officer in Japan's Tokko Suicide Regiment

Below is an excerpt from Mr. Tadamasa Iwai's Book.
It is available for sale in Japanese only, but Mr. Iwai provides
an English-language excerpt below.


Explanation of special attacking weapons “Kaiten” and “Fukuryu”
(extract from my book “Tokko”)

About “Special attack” in general: It is widely known and need not make detailed explanation about the fact that the Japanese Navy, having achieved great gains in Pearl Harbor and in Malayan Sea at an early stage of the War, was beaten in the Battle of Midway and, after this, it repeated defeats everywhere it fought under overwhelming predominance of the American Navy and Air Force. Going with those defeats, the Japanese Navy rapidly lost many battleships, cruisers, carriers, aircrafts and combatants and it was anticipated that final defeat would come soon. In such a hopeless situation the special attack tactics was conceived by the Japanese military, having been deprived of all other effective means. This tactics was named afterwards “Tokko”, which means “special attack” and the word “special” was a euphemistic expression of “suicidal”.

The special attackers consisted of young men: teen aged volunteers, reserved officers (officers coming from students were called so) and professional ones.

The first special attack called “Kamikaze” was the one made by planes against the American landing operation on the Philippines in December 1944. . .

(Note: The word “Kamikaze” originally means “God’s wind”. In 1274 and 1281 Japan was attacked by Kublai Khan’s force of Yuan (Mongolia now).

But the attacks ended in failure due to typhoons happened by chance which sank almost all the Mongolian warships and Japan won them. The typhoons were named “Kamikaze” and the belief came out among Japanese people that in any emergency God would help Japan by his supernatural power. The suicide attacks made by Japanese military in the War were given that name after this ancient origin and setting slightest hopes of victory.)

But already at that time, not yet having been applied, other types of special attack tactics using other means than airplanes had been contrived, weapons had been produced for those purposes, troops had been organized and exercise had begun: small-sized submarines called “Kairyu” and “Koryu”, wooden motorboat called “Shin-yo” etc. I make explanations only about Kaiten and Fukuryu under.

About “Kaiten”: This was a torpedo altered to be operated by a pilot on board i.e. human torpedo. As known originally, torpedo is not made for getting on. Having been shot out from a ship or dropped down from an airplane it only dashes forward underwater by itself to the direction determined beforehand by means of built-in gyro mechanism. Among normal torpedoes the type numbered “93” had special superiorities to others and Kaiten torpedo was made utilizing this type.

(Note: The word “Kaiten” means “Revolution of heaven” and the name was adopted perhaps hoping complete recovery of the unfavourable war situation.)

In case of normal torpedo other than 93-type the engine is supplied with kerosene and compressed normal air, which consists of about 22 % oxygen and 78 % nitrogen. So the exhaust gas discharged from the engine contains a large amount of nitrogen gas as it stands and the bubbles of which make a distinct wake making the torpedo easily findable.

But in case of 93-type pure oxygen was used instead of normal air, of course compressed. Therefore nitrogen was not included in its exhaust gas and so this type ran not leaving striking wake, as the steam in the discharged exhaust gas united at once with the sea waterÅAthe carbonic acid gas was readily soluble in water and no nitrogen gas made bubbles. These characters made the torpedo unfindable. Moreover it was helpful in raising the power output of the engine as well as in extending the cruising range. So the Japanese Navy was proud of this type of torpedo very much and made it a top secret. Kaiten torpedo inherited these superiorities of 93-type torpedo.

Kaiten torpedo consisted of two parts: the hind part of 93-type torpedo (the part with an air flask, a fuel flask, an engine, fins and double propellers turning to reverse directions) and a big shell with a diameter of one meter added to it which contained upper and lower hatches, controlling device, a seat for pilot, a small-sized periscope, an auxiliary air flask and an explosive charge at the top. Total length was about 15 meters (16 yd. See Ill. 1). Every part was made watertight, of course.

It ran underwater at 30 knots per an hour with the same engine as the original 93-type torpedo. The explosive charge loaded at the top weighed as much as 1.6 tons (about 3,500 lb) and its explosive power was enormous enough to send any huge battleship to the bottom within one minute, we heard.

“Kaiten” differed in the character from normal torpedo in the following points:

In case of normal torpedo including 93-type the moving direction is determined by built-in gyro-compass before shooting out and it runs straight on keeping the determined direction. It is impossible, of course, to change the moving direction or running speed after shooting.

The moving direction of Kaiten was determined by means of gyro-compass, too. But it could be changed by adjusting the gyro-compass by the pilot on board with his hand and thereby he could control vertical rudders and change traveling direction freely after departure. Running depth could be adjusted by controlling horizontal rudders and running speed also by adjusting feeding amount of fuel and oxygen to the engine. It could rise onto the surface of the sea and make scouting with the periscope.

Thus, Kaiten torpedo had controllability owing to the embarkation of man. But it inherited some defects from the original: it was impossible to go back and to re-set the engine which once stopped, because the engine for original torpedo was converted intact to it: though the traveling direction could be changed, the rudders worked ineffectively and its turning radius was as large as about 200 meters (about 183 yards), as they were small and installed before the propellers.

Anyway the controllability of Kaiten must have raised its accuracy rate in theory. But, in fact, in most of the cases attacking results could not be identified. And its hit must inevitably bring death to the pilot on board. There was no escaping device.

Kaiten torpedo could not be shot out from torpedo tube like the normal one, as its size was too large. So it must be launched from the deck of a submarine which had been loaded with it. (Usually one submarine was loaded on its deck with 4?6 Kaiten torpedoes). Only after announcement of beginning of “Kaiten battle” the pilot got on it, the lower hatch was closed and then it was liberated.

Thus many pilots went on board submarines to the southern seas in such a way and lost their lives. Not a few were killed before they got on the torpedoes together with the crewmembers of the submarines sent to the bottom by depth charge attacks from hostile vessels.

Despite its superiorities in functions the mechanism of Kaiten torpedo was considerably imperfect, as it was merely a remodel of normal torpedo. And not a few pilot were killed with accidents caused by various troubles still during exercise. There were often such cases when pilot who had departed on board submarine for fighting from his base returned in vain with the submarine for the sake of mechanical breakdown found before launching of the Kaiten torpedo or failure in finding target vessel.

In case when, after launching, the Kaiten failed to find a target vessel it could not return to the mother ship. Because she must have seceded from the launching point in order to avoid enemy’s attack. In such a case, therefore, Kaiten was obliged to carry out self-destruction by means of equipment for this purpose. Having once launched, it was the pilot’s doom to depart this life, regardless if his attack was successful or not. Inevitable death of pilots had been counted in from the planning stage.

About “Fukuryu”: Very few people still know the existence of such special attacking weapon at the time of the War, because, perhaps, it was hurriedly contrived at the latest stage of the War but not applied to the actual fighting.

(Note: The word “Fukuryu” means “Crouching dragon”. The reason why the Fukuryu bore this name is unknown.)

Fukuryu was one of “special” attack tactics contrived by Japanese Navy in the early summer 1945 in order to hinder the expected U.S. Forces’ landing operations on the Japanese mainland, when Okinawa islands had been already captured by U.S. Army. The idea of Fukuryu tactics was as follows: troop of Fukury-divers is to be stationed in water near seashore at the expected landing place of enemy troops: each of Fukuryu-divers wears special diving helmet and suit with two oxygen bottles on his back and carries in hand a small-sized portable mine fixed to the top of a bamboo pole. They waits for hostile landing crafts dashing to the seashore in the water and hit their bottoms with the mines. Success of such attack, if any, meant not only blast of the hostile craft and soldiers on board but also inevitable death of the attacker himself, of course. (See Ill.2).

In any other special attacking tactics something vehicle-like was used: airplane (Kamikaze), small-sized submarines (Kairyu and Koryu), small-sized motorboat (Shin-yo) or human torpedo (Kaiten). These vehicles threw themselves at the hostile ships in their ways. But in case of Fukuryu no vehicle was used but, instead, walking on foot on the seafloor was its only moving method. Fkuryu diver could not swim as the suit was very heavy. .

Anyone who learns of this tactics is astonished and understands that this plan was too harsh and too primitive to fight against American corps armed with modern weapons. And it proved how the Japanese Navy at that time came to a dead end and how Japanese state made light of people’s lives. Exercise was carried out but, happily, it was not applied to actual fighting after all. But not a few divers were killed with accident still during exercise in the water. I also fell unconscious during exercise in the water and had a narrow escape from death. I will give a full account of the accident later.

Because the purpose of Fukuryu tactics was as mentioned above, it was impossible for the Fukuryu diver to be supplied with air through a pump from ground or vessel like for normal diver was. He breathed oxygen gas receiving from two oxygen bottles settled on his back. Exhaled breath was blown into the absorbing (purifying) box on his back through a rubber tube, being deprived of carbonic acid here the purified oxygen was sent into the helmet and breathed again. When the oxygen for inhaling was consumed to a certain extent it was supplied from the bottles on the back by controlling a supplying valve. In the absorbing box there were thin sticks of soda hydroxide which played role of absorbent of carbonic acid contained in the exhaled breath.

The diver must avoid inhaling carbonic acid gas contained in his own exhaled breath. So he must inhale through nose and exhale into the mouthpiece attached inside of the helmet sticking his mouth to it. Inhaling through nose and exhaling through mouth into the mouthpiece? it was the most important way of breathing for the diver. If he does not observe this rule he will soon fall unconscious or, in the worst case, go to death.

The diving suit was coated with rubber (converted from gasproof cover , as I heard) and consisted of two parts -- upper and lower -- which were connected about the waist. Different from modern tight wet suit it was very loose and looked like space suit which astronaut wears when he works out of the space craft. Even if the awkwardness was ignored, it was very heavy and disturbed moving.

There were some reasons why oxygen was used instead of normal air as mentioned under:

It allows to stay longer in the water;

It prevents caisson disease;

It makes Fukuryu diver unfindable as he need not discharge each exhaled breath into water.

The special diving suit for Fukuryu was considerably heavy, as the helmet, its holder around the neck and two oxygen bottles were of iron. Moreover to the suit belonged an absorbing box, various metal fittings and rubber tubes etc. They were settled almost all on his back. So the diver put on lead sandals and attached a lead ballast on his abdomen in order to lower the center of gravity. Therefore the diver carried a load as heavy as about 60kg (160 lb) altogether according to my memory. This weight made it hard to walk on land and the diver was liberated from the difficulty only in water.

The diver must always hold a posture bending forward in water as heavy things were all on his back, or he was turned over just as a tortoise flipped over and, once he fell into such position, it was almost impossible to restore normal posture and work in some way or other.

The Fukuryu diver, wearing such special suit, carried in his hand a bamboo rod with a small- sized mine at its top. The mine had a horn made of glass and covered by rubber at the top detonating on contact. This special mine was developed only for Fukuryu-tactics. But we were not given the mine for practical use but the one only for exercise.

Normal mine is a weapon which is laid beforehand in the hostile watercourse expecting hostile ship carelessly passing on it and so its how to use is passive. But in the case of Fukuryu the attacker in the water hits the mine against the hostile craft, so the how to use is active.