Plans were being concocted for a one-man midget which could be released while the mother submarine was submerged. During the winter of 1942-43 two naval officers, lieutenants Nishina and Kuroki, and a naval architect Hiroshi Suzukawa drafted a design based on the Type 93 Long Lance. All the major components of the original torpedo were retained, and the only major modification was the inclusion of an additional section between the warhead in the nose and the oxygen motor. This was the pilot’s compartment, fitted with a periscope and a set of controls enabling a man to direct the torpedo run. By the spring of 1943 the designers had completed their drawings, and had calculated that their ‘manned’ torpedo, fitted with a 3,000 pound high explosive warhead, would have a range of forty nautical miles. The Long Lance had already proved it could break the back of a heavy cruiser with a man to direct it and a warhead three times more powerful there was every reason to suppose it could do the same to a battleship or an aircraft carrier.
Things had already started to go badly for the Imperial Navy and the Naval General Staff in Tokyo were looking for some way of changing the pattern of the Pacific war. The plans were presented for what the designers were now calling the kaiten. (The literal translation of kaiten is ‘Heaven Shaker’. But in Japanese it means much more – suggesting a radical change in affairs.) But they were rejected as being too fantastic even But when the for consideration. Imperial Navy’s attempt to smash the Americans at Saipan went awry the men in Tokyo began to have second thoughts about the kaiten. Nishina and Kuroki’s persistent pleas to the Navy Ministry had culminated in a petition written in their own if this had much what undoubtedly caused the Naval General Staff to listen was what the Americans termed the ‘Marianas Turkey Shoot.’ when over blood. It is doubtful effect; 400 Japanese planes were lost. Thirteen months after they first sought it, permission was given for the construction of a prototype. But only on condition that it should have an escape hatch giving the kaiten pilot a chance to get away safely once he had put his weapon on a sure course to the tar- get. In February 1944 the prototype was approved and a base was set up on Otsujima Island near the Kure naval base, headquarters of Japan’s Sixth Fleet and submarine force.
Strict security measures kept news of the project out of the public eye and only a few kaiten had been built by June 1944. But when the extent of the disaster which had overtaken the Imperial Navy in the Marianas finally dawned on them, the Naval General Staff sent out a frantic order for more to be produced on a crash priority. A second order called for volunteers to operate a Kyukoko heiki, a new national salvation weapon, on missions from which they were not expected to return alive. At first no mention was made of the nature of the weapon, but even when it was learned that their probable fate was an unseen death beneath the waves there were plenty of volunteers. Indeed it appears that the first ones were grateful at being accepted. Selection was supposedly based on three qualifications: physical and moral strength, evidence of strong sense of patriotism, and a minimum of family responsibilities. Married men were excluded and very few elder or only sons were chosen. The accent was on young fit men who would have little tendency to look over their shoulders.
At the kaiten depot on Otsushima, ‘Base P’, every effort was made to instill esprit de corps, Yamato damashii, Japanese spirit, in the volunteers. On arrival they were introduced to a prototype of their steel coffins before being shown to their quarters. The latter were, like their food, luxurious in comparison with what most of them had known in their previous training. But there were few recreation facilities – no cinema and no women. Nor were the men permitted leave of absence until they had completed their training, and were ready for the mission which was to be their finale.
Nishina and Kuroki organised the training of the first volunteers. But on 6th September, 1944, the kaiten claimed its first victim when Kuroki’s torpedo stuck in the mud at the bottom of the placid waters of the Inland Sea. Six other lives were to be lost in training before the end of the war brought the demise of the kaiten. But, from September 1944 until the end of the Okinawa campaign, volunteers in groups which were given traditional names such as ‘God’s warriors’, ‘Group for the furtherance of the Samurai way’, took kaiten courses at Otsushima. Lessons in the functions of the Type 93 torpedo were followed by simulated dry run missions to familiarise the pilots with the controls and accustom them to the confined space of their tiny cabin. Submerged practice drill against ships moored in Tokuyami Bay followed. Finally, when the pilots were considered proficient at these drills, the group was embarked on one of the fleet submarines for an operational dummy run.
Each of the I class submarines fitted to carry kaiten could take six of the weapons. During the approach to the target the kaiten pilots climbed into their tiny craft through a special hatch which was then sealed off. As the submarine closed on its victim, a telephone link between the submarine’s conning tower and the kaiten enabled the captain to keep the pilots informed on the relative positions of the target. At the optimum moment the kaiten’s engines were started and they were released at five-second intervals from the mother ship. Once in motion the pilot could observe the target through his own periscope, and make the necessary corrections to his course. Then at about 500 yards distance he would switch his craft on to automatic control for the final dash at full speed submerged to a depth of about twelve feet.
Inside the kaiten even a small man was cramped. And, although the controls were simple, considerable skill needed to operate the craft Under his feet was a tiny box of emergency rations and a small flask of Japanese whiskey. Neither was intended for operational missions. Directly in front of the pilot’s face was the viewing glass of the short, stubby periscope which was raised or lowered by a crank on the right. Also on the right but above the pilot’s head was the valve regulating the oxygen flow to the motor immediately behind him. Overhead on the left was a lever connected with the kaiten’s diving planes, which controlled the rate of descent or climb underwater. Below efficiently. was a valve for letting in sea water. This was necessary to maintain stability as the oxygen fuel was used up. Finally, there was the rudder control lever which steered the weapon right or left and which was the last control to be touched by the pilot when he set his final course for an enemy ship. To operate the kaiten efficiently a man really needed six hands. And about the same number of eyes for watching the control panel. Apart from the periscope there was a gyrocompass, a clock, and depth and fuel gauges. Any sudden change in the controls or contact with an underwater obstacle invariably resulted in the pilot banging his head on one or other of the instruments. In consequence, bandaged heads were a frequent sight on Otsushima.
On an operational mission the captain of the mother submarine would align his ship with the target and this lever man would check his compass bearing. In the conning tower each kaiten the attack course of each individual kaiten would then be plotted and relayed by telephone. For example a typical order might be ‘Go right thirty degrees on leaving. Speed twenty-five knots for twelve minutes and thirty seconds.’ These instructions were designed to bring the kaiten to within 500 yards of his target, at which point the pilot was expected to raise his periscope and set the controls for his dash for the enemy ship’s vitals at the top speed of forty knots.
Training finished with the successful completion of an operational dummy run. The kaiten men were then entitled to a few days leave before assignment to an operational mission. On this leave they were not expected to reveal the fact that they were now committed to a suicide operation. Nevertheless many of the families of such men appear to have guessed the reason for the special leave even if they were not told. Any suspicions they may have had would often be confirmed by little luxuries with which their relative was laden when he arrived. When the leave was over it was not considered good taste to mention that the next meeting would probably be at Yasukuni. But no doubt the thought was there.