A less known unit of the Imperial Japanese Navy was the Special Harbor Defense and Underwater Attack Unit - Tokyo Bay.
– FUKURYU –
These divers used rubber diving suites with a circular breath system. The air contains only 23 % oxigen and this spent oxigen was replaced by two steel 3,5 liter compressed oxigen bottles by a valve/pressure device. The poisonous CO² we breath out was bound by a Calciumoxid purifier cartridge. There are no bubbles or wakes visible at the surface.
These system was known from U Boat safe and breath devices. 1000 suits where completed. 10000 more was ordered. The system was simple and effective and several suits where shipped to the USA for closer tests and examination.
This suite enabled trained divers to be submerged for 8 hours in about 8 meter deep water. For a longer time the oxigen breathing become poisonous for the body in more than 10 meter deep water. It was no problem to walk about 2000 meter in a hour. A liquid food was developed and the diver could eat underwater with a small hose.
Shortly for trained persons 35 meter where possible and the suite improved every day. At the end of the war 4000 men served in the unit, 1200 men where well trained. Every man got a wrist compass and a flashlight.
The weapon was a sort of lance mine - the Type 5 attack mine. It was
3,3 meter long with a 56 cm long sheet metal container holding a 10 Kg TNT charge. The rest of the container was empty and used as a floating chamber.
Ignited by a 12cm long horn fuze very similar to, if not the fuze used on sea mines.
The diver simply push the mine against a ship. The tested safety range between each diver was app. 60 meter.
Submerged concrete installations and sunken ships with a diver chamber shouldt be bases for several divers equipped with food, water and oxigen bottles.
Normal mines and underwater explosives should be used too. Even underwater torpedo facilities where build. May be they are still there today.
This is a memorial statue in a japanese museum
Any additional information about this subject is very welcome.
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