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The Japanese word Kaiten means heaven-shaker and  was given to a secret weapon used by the Japanese towards the end of World War D.  The Kaiten was a modified torpedo carrying 3,000 pounds of high explosives and launched from the deck of a fleet submarine.  As only one of several suicide weapons developed by the Japanese, a human pilot would guide the Kaiten weapon  to  its target.   Although  some  believe the  Kaiten was relatively successful during the last three months of the war, it was highly criticized from both an economic and a humanity stand-point.   Not  only  was  an  expensive  torpedo  destroyed,  but  a valuable manpower resource as well.  The Japanese industrial base was almost totally exhausted by the time Kaitens were employed and it was impossible to produce the amount of Kaiten weapons and mother  submarines  required  to attain the expected results. More importantly, the loss of manpower deemed essential in the operation of the weapon,  would not be replaced  for  an  entire generation.

The mere concept of a suicide weapon was against the Japanese tenet of “Death in war is inevitable, but it should not be pointless-ly courted”. (Ito, page 162) The development of such weapons to include: the Kaiten, Kamikaze, Obka (glider, Shinyo (motor-boat), and Fukurya (swimmers) shows the desperation that the Japanese leadership felt knowing they had lost the war. The disaster at Midway was followed by substantial naval defeats in the Gilbert, Marshall, Solomons, and Marianas Islands and the threat of an invasion of the Japanese mainland was increasing each day. Most of their naval ships and aircraft carriers bad been destroyed and along with them, their superior aircraft and pilots. Addition-ally, unlike the German U-boats in the Atlantic, Japanese subma-rines were employed poorly and made little contribution to the war.

The war was not going the way the Japanese High Command had planned and the suicide weapons were a last ditch effort to bring about a tremendous change and win the war. In fact, a quote from one of the Kaiten inventors, illustrates the desperate thinking of the Japanese.

“It must be obvious that the American fleet will have to use atolls for anchorages, for their westernmost large base is at Pearl Harbor! Now then, if the American fleet anchored in such atolls, what better weapon is there than a Kaiten for attacking these task forces? Just four submarines, carrying four Kaiten each, could be on the enemy before he suspect-ed their presence, launch Kaiten, and retreat. The Kaiten would penetrate the atoll, and 16 enemy ships would be sunk at one blow. Imagine trying to dodge a weapon that is faster than any ship, especially when you are in a crowded anc~orage. Our weapon could reverse the way this war is going. We could still win it!” (Yokota, page Unfortunately, the employment strategy proposed by the inventors yielded poor results for both the mother submarines and the Kaiten.

Even when it was obvious the Japanese would be defeated, they refused to give up. Instead they went to extremes to develop suicide weapons in hope that these weapons would change the outcome of the war. Evidence of this never say die attitude is shown in the Kaiten pilots wearing hachimaki (white bandanna) to signify relentless determination. Three aspects of the Kaiten-the weapon, the men and the results-let us better understand this desperate measure by the Japanese.

The Weapon

After the Japanese defeat in the Solomons, Lieutenant Junior Grade Hiroski Kuroki and Ensign Sekio Nishina, both pilots of midget submarines. conceived the idea of the human torpedo. Midgets were small battery powered submarines which carried only two torpedoes and participated in the attacks on both Pearl Harbor and Midway. Although the Imperial Japanese Navy considered them valuable weapons, they had many limitations: low speed, lack of maneuverability, ability to operate only near shores, and long launching time from the mother submarine. So Kuroki and Nishina concluded that what was needed was a better weapon-one that had more accuracy and high speed.

Fortunately for Kuroki and Nishina, Japan already possessed the oxygen-powered Model 93, Long Lance Torpedo. This potent torpedo could travel 22,000 meters at 50 knots and was never matched by the United States nor the British. While conventional torpedoes left an obvious bubbly wake, the Model 93 left no track.

“A torpedo which had greater range than the biggest gun of a battleship provided the opportunity for a revolution in surface actions.” (Ito, page 195)

The final design for the Kaiten weapon was completed in January 1943 and required a few modifications to the Long Lance Torpedo. These modifications included removing the warhead and inserting a pilot’s compartment, a periscope and a set of controls. Then the warhead would be replaced and the torpedo reassembled. With these modifications, the Model 93 torpedo could be trans-formed into a secret weapon that was undetectable, powerful enough to sink a large ship and had precision control to the target.

With high hopes that their weapon would change the way the war in the Pacific was going, Kurold and Nishina set off to sell their plan to the Japanese General Staff. They initially got nowhere. Prime Minister Kantaro Suzuki said

“Using men in a situation where there is no chance of survival is not proper military operation. The Japanese Navy has always opposed such undertakings. (Ito, page 192)

However, as the war became more desperate and news of what Americans called the Marianas Turkey Shoot (the loss of over 400 Japanese planes in that engagement) reached the Japanese High Command, they finally accepted the suicide weapon. Realizing the Kaiten was inhumane, there was no apparent alternative-Japan’s resources and industrial capability were almost exhausted.

Nearly 13 months after Kurold and Nishina first approached the Japanese General Staff, their prototype design was finally ap-proved. A secret base was set up on Otsujima Island in Tokuyama Bay, Yamaguchi Prefecture, with Lieutenant Commander Mitsuma ltakura as the first commanding officer. (Orita, page 232) Lieutenant Kurold and Lieutenant Junior Grade Nishina, both promoted, became the chief instructors as well as Kaiten pilots. Unfortunately, even before the Kaiten program was off the ground, disaster struck. Lieutenant Kuroki and another student Lieutenant Higuchi drowned when their Kaiten cracked and flooded after it took a sudden dip and struck bottom. The Kaiten was recovered and the bodies were cremated. Nishina vowed to carry Kuroki’s ashes with him on the first Kaiten mission, which subsequently occurred near the Ulithi Atoll at 4:15 AM on November 22, 1944.

Although seemingly simple, the operation of a Kaiten was rather complex. Once a target was sighted, the submarine captain would order the Kaiten pilot to this weapon (a fleet submarine could carry up to six Kaiten). The pilot would enter his Kaiten weapon through a special hatch, which would then be sealed off. As the submarine closed on the target, relative position and other information would be passed to the pilot via a telephone. At the optimum moment, the Kaiten pilot would release the remaining two cables holding his torpedo in place and then start his engine. From then on, the Kaiten pilot was on his own. Using his single-eyepiece periscope, the pilot could make periodic spot checks of th~ target and correct his course if necessary. The pilot could control his speed by turning the oxygen valve overhead which regulated the oxygen flow to the engine. Additionally, there was a crank to regulate the rate of descent or climb underwater and a valve on the left for letting in sea water to maintain stability as the oxygen was used up. Finally, on the right there was a rudder control lever to steer the torpedo. Words from an actual Kaiten pilot, Yutaka Yokota, who survived the war, illustrate the complexity of the weapon:

“A man had to have about six hands for operating a Kaiten. And about the same number of eyes for watching its control panel. There was an air-driven gyrocompass, a clock , a depth meter, a fuel gauge and an oxygen pressure gauge to keep an eye on, and that periscope was close by, always ready to gash your skull in if you moved too suddenly or knocked into some underwater object.” (Yokota, page 63)

The Kaiten weapon, compared to the high tech weapons of today, was a crude machine which required a skilled pilot. However, the determined Japanese pilots were able to master the complex controls in just a few underwater training sessions.

The Men

Japanese men were expected to fight, and die if necessary, for their country simply because it was their duty. It was Japanese tradition that no one ever received medals while they were still alive-the privilege of fighting or dying was enough. It is with this tradition that the Kaiten weapon was brought to life.

A total of 200 volunteers for the secret weapon were solicited from two naval air training bases, Nara and Tsuchiura. The men were not told what the secret weapon was, only that whoever mans the weapon would not return alive. The men were then asked to draw two circles on a piece of paper if they really wanted to volunteer, only one circle if they didn’t really want to go at all. Because so many men volunteered to die for their country, they had to be screened. No married men were allowed and only the top 100 men from each base were accepted.

The volunteers arrived at the secret Kaiten base of Otsujima towards the end of August 1944, where 30 men were already in training (a second base at Kiari was created a few months later). Lieutenant Commander Italcura addressed the new recruits and showed them the Kaiten weapon. For security reasons, he instructed them to refer to the Kaiten as maru roku kanamorw– circle six metal fitting. With that, classes began at once on the construction, maintenance and control of the Kaiten weapon. Due to the limited number of Kaiten training torpedoes, it would be some time before the new recruits would experience the thrill of operating one underwater.

The men, who bad decided to die for their country, grew impatient waiting for their chance to prove themselves. When not out in a Kaiten, the men would practice how to estimate the range, course, and speed of a ship accurately, practice identifying American warships, participate in physical exercise and assist on torpedo boats. Anything to stay busy.

Japanese training methods would be considered harsh in American terms. Trainees were punched or slapped for making a mistake or forgetting to do something. Such methods are evident in Petty Officer Yutaka Yokota’s account of an incident that happened after he had made a poor training run in his Kaiten:

“Lieutenant Hamaguchi (training officer) was full of rage when I climbed out of the Kaiten and stood before him. You fool! be said, and punched my face. You fool! You could have killed yourself. Do you know what that would mean? It would mean you had given back the enemy one ship! How can we sink enemy ships if fools like you are going to kill themselves before they every go into action? Get out of my sight!” (Yokota, page 89)

Furthermore, the Imperial Navy principle ofmass punishment was applied routinely. When one person made a mistake, then the whole group was punished.

Although training was harsh, the respect given to a Kaiten pilot was enormous. They were considered elite and had been granted the great privilege of dying for their country. A shrine was even built to honor them. On the eve of the first Kaiten mission, a special ceremony was conducted for the 12 men (four Kaiten each were attached to three modified submarines, 1-36, 1-37 and 1-47). Vice Admiral Shigeyoshi Miwa, Commander of the Sixth Fleet, presented each man a short sword. The sword was an important symbol for Japanese fighting men. They must fight honorable to victory or use the sword to commit seppuka or what we call hara kiri.

“Once this sword was presented, a life was pledged for the Empire, either through battle death or disembowelment.” (Yokota, page 44)

Following the ceremony, the officers held a party to honor the 12 heroes. Sake was poured and all enjoyed a fine traditional Japanese meal, even though, by late 1944 there was a shortage of everything. The next morning a band played the Japanese National Anthem while the Kaiten men boarded their submarines. Before boarding though, the men made sure all their earthly possessions including bits of hair and fingernail partings, were packed for shipment to their loved ones. As the men stood proudly on their Kaitens, a crowd cheered as the submarines moved out of the harbor.

Once the submarines were enroute to their targets, 1-36 and 1- 47 to the Ulithi Atoll and I-37 to the Kossol Strait, the Captain’s dilemma began. He had to provide some men the means for death, and the others a means for life. He would have to order men to die and in a sense, become their executioner. Many agonizing moments were spent trying to come to terms with this dilemma. (Orita, page 240)

The night before the first Kaiten operation near the Ulithi Atoll, the men made their final preparations. They packed their spare uniforms, other belongings and wrote any last notes. One pilot wrote this note to his mother:

“My hearts breaks when I think of how you will be provid-ed for. Your words that one should die nobly for our country are strong in my mind as I leave on a mission from which there is no return. Please take good care of your self. (Ito, page 211)

These young men gave the ultimate sacrifice for their country dying with bravery and grace-they loved their parents, families and sweethearts and above all, their country.

Not all Kaiten were launched on the first mission, primarily because of mechanical failures. This was a great disappointtnent to the intense young men who were full of courage and determina-tion. They returned to base in hope that they would go back out immediately with a new Kaiten in perfect condition. However to their surprise, once they returned to base, they were viewed as cowards. Yutaka Yokota gives another interesting account of the intense humiliation felt by the returned Kaiten pilots after a poor training performance.

“The new executive officer slammed his bamboo pointer down on a table. You should be ashamed of yourself, Normural he shouted. As for the rest of you, it is no wonder that one or two of you come back from each mission, without being launched at a target. What is your hachimalci for? And your sword! Doesn’t it mean anything at all to your spirits? And the big send~ff given you by all hands when you leave on a mission. These things are not done so that you can tum around and come back again! Once at sea, you must overwhelm the enemy! If anything goes wrong with you Kaiten, fix itt If the propeller won’t spin, tum it with your bare hands I Crash into the enemy, no matter what! That’s what the Kaiten is fori (Yokota, page 200)

After the announcement of the unconditional su”ender ofJapan on August 15, 1945, the remaining Kaiten pilots were in shock.

“It is simply impossible for us, all dedicated men who had long ago offered to die for Japan, to accept the fact that our Emperor was now ordering to live.” (Yokota, page 246)

They had seen their friends go off and die and felt that the surrender was a betrayal of them. They had no desire to live. Fortunately, an admiral who was concerned about the well-being of the human torpedo volunteers, devised a plan to form a fanning force. He donated a piece of land, where all Kaiten men who wanted to retreat from the world, could join his force. Eleven men, all emotionally unsettled, tilled the land and planted crops until they were ready to make a new life for themselves.

The Results

When the Kaiten program ended, 88 pilots had been killed in action, with an additional 15 killed in training accidents. Addi-tionally. eight submarines, with crews totalling over 600 men, were sunlc while seeking the enemy for Kaiten operations. For this enormous loss of life, the Japanese Sixth Fleet estimated that Kaiten pilots were responsible for sinking between 40-50 enemy ships. However, only two U.S. tankers and one U.S. merchant ship can be confirmed by U.S. records.

There are many reasons why the Kaiten weapon failed to achieve significant results. First, like the Japanese submarine force, the Kaitens were ineffectively employed. Instead of attacking enemy shipping and sea lines of communications, they were initially employed against naval ships in well protected harbors. The enemy’ s anti-submarine warfare tactics and radar proved to be extremely deadly to Japanese submarines. Even if the submarine was lucky enough to survive a depth charge attack by the enemy, the Kaitens they were carrying were usually damaged. Additionally, the Kaiten’s hull was only one-fourth of an inch thick and could not withstand the pressure of a deep dive. Thus, the submarine’s defensive actions were severely hampered. Consequently, when the Kaitens were finally employed against enemy shipping, they achieved impressive results (note: results have not been confirmed by U.S . records). In the last three months of the war, nine submarines carrying Kaiten weapons sunk15 tankers and transports, two cruisers, five destroyers, one seaplane tender, and six unidentified ships; and damaged two ships. (Ito, page 199)

Second, the Kaiten was a complex mechanical weapon, where lots of things could go wrong. Take for example I-36’s maiden voyage. At the moment set for firing, the No. 1 and No. 2 Kaitens were stuck fast to their racks and No. 4 Kaiten was leaking oil. 1-36 was only able to launch one Kaiten for the entire mission.

“Of the 24 Kaiten sent out with the Kongo Group, only fourteen were launched at the enemy. ” (Yokota, page 55)

Electronic problems also plagued the Kaiten. Essential informa-tion had to be passed to the pilot over telephone lines when he was sealed inside his Kaiten and without the updated information the Kaiten could not be launched. Furthermore, once the Kaiten was launched, the possibility existed that one of the many controls or valves would malfunction and cause disaster for the Kaiten.

Third, there were not enough mother submarines nor Kaiten weapons. The Japanese lost a total of 130 submarines during the war and by August 1945, they only had seven operational subma-rines left-even the heaven-shaker could not change the tide of the war. At the time of the first Kaiten mission only three submarines were converted to carry Kaitens, the rest were being used to transport much needed supplies to stranded Japanese forces. Additionally, Kaiten torpedoes were in short supply which delayed actual hands-on training for most of the pilots.


The Japanese in World War n were convinced that the human torpedo would give them the advantage and that somehow they could still win. Having lost most of their military force in one disaster after another following Midway, the Japanese knew that defeat was at their doorstep, but they refused to give up. They chose instead to develop weapons with infallible control mecha-nisms-human pilots. It was the determined will of the Japanese people that allowed such a weapon to be developed, for it was considered a great honor to be selected to die for your country.

With a few modifications, Japan’s superior torpedo, the Model 93 Long Lance, was transformed into a highly accurate, undetectable, and powerful secret weapon. The men endured rigid training to become respected heroes of the Japanese people.

The Kaiten could have achieved substantial results, bad the I apanese employed them effectively, developed sufficient numbers of weapons and mother submarines, and been able to fix the mechanical problems plaguing the weapons. As it turned out, the Kaiten was too little too lale to change the war in their favor.

Consequently, the Japanese desperate and inhumane effort to develop a secret weapon to change the outcome of the war was futile. It expended both scarce torpedoes and valuable manpower resources, without achieving any significant results. The patriotic men who volunteered as Kaiten pilots and the crews of the submarines that carried the Kaiten, died in vain.

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