Most Americans are familiar with the Kamikaze air forces of World War II Imperial Japan. Yet few know there was an underwater force created to do battle with American landing craft and vessels rushing the island nation during the expected invasion. While the atomic bombs changed the need for invasion plans, those countermeasures drafted by the Japanese resulted in the Fukuryu, or Crouching Dragons.
The frogmen were at first volunteers from the trainee pilot corps of the Japanese air force. They were to don a completely enclosed diving suit and helmet, outfitted with a self contained underwater breathing apparatus (SCUBA.) Upon the first waves of allied landing craft, the suicide frogmen would begin their defense by piercing the hulls of soldier laden U.S. vessels.
Japanese Navy tests revealed the Fukuryu could work along the bottom at a depth of 15 meters for up to eight hours. They were also expected to walk along the harbor floor at a rate of 2,000 meters per hour while carrying their primary weapon- the Type 5 Attack (Suicide) Mine.
The mine was essentially an explosive packed container at the tip of a several foot long pole. The head of the pole was the mine, filled with 21 pounds of TNT. The Fukuryu would walk out amid the invasion overhead and lance the bottoms of the landing craft, detonating the mine and destroying the vessel. However, the charge would result in the death of the Fukuryu as well. To prevent one diver killing another during assaults, minimum safe distances were established for the Crouching Dragons.
The Japanese suicide divers would lay and deploy mines as a first line of defense. The Fukuryu would then comprise the next three layers of suicide defense, ranks deployed along the ocean bottom at depths between 12 and 19 feet, suicide mine poles in hand.
However, the innovation expressed by these last-gasp defense measures didn't end with the Fukuryu. The Japanese laid the ground work for a series of subterranean tunnels that would allow the suicide mine bearers to enter and exit the water without being seen.
Even more ambitious were plans to construct underwater domiciles for the Fukuryu. These shelters, pressurized and equipped for several men, would allow the suicide divers to deploy at will from within a wrecked ship. The ship would provide cover for the troops barracked inside, creating in essence, underwater pillboxes.
The use of a ship as cover and base for seaborne troops was also used by the Naval Commando units of Benito Mussolini. His Decima Flotilla used the Italian cargo ship the SS Olterra as a floating base off Gibraltar. The Italian frogmen came and went from the staging ship via a secret hatch at the ship's waterline.
For all the development in both weapons and the vitally important SCUBA units and diving suits, the Fukuryu never saw combat.