F-Go Navy Project
The Imperial Japanese Navy (IJN) decided to create it's own Atomic bomb project in 1943. Known informally as the Kyoto Group, IJN funded a team around the maverick scientist Prof Arakatsu with 600,000 yen in March 1943.
The Imperial Japanese Navy (IJN) project to enrich Uranium 235 was led by rear Admiral Nitta Shigeru. Nitta worked closely during early stages of the project from 1942 to 1944 on isotope separation with Sakae Shimizu . Dr. Shimuzu developed F-Go’s gaseous Uranium centrifuges.
IJN’s centrifuges were developed by a company specialised in precision ship gyros, Hokushine Electric Company with assistance from Tokyo Keiki Electric Co. These were built under contract by heavy engineering firm Sumitomo. Centrifuges were constructed from Rare earth metal alloys and spun at between 100,000 to 150,000 RPM.
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This was an impressive speed since even today the best centrifuges only operate at about 50,000 RPM. The measure of efficiency for any centrifuge at enriching Uranium depends upon the speed at which the centrifuge spins. It has been claimed that these centrifuges were never built, but the revolution could not be known without testing of an actual prototype machine. The biggest hurdles for any centrifuge are in creating bearings and rotor drums able to withstand the enormous forces involved. the earliest rotors used aluminium rotors, Subsequently maraging steel construction allowed even higher speeds, but the Japanese used alloys with Rare Earth metals to create exceptionally strong rotor drums. The Nazis developed carbon fibre brushes and may have shared these concepts with Japan.

Prof Arakatsu seated with Dr Kimura standing
Leading nuclear theorists for the Naval A-bomb were Professor Arakatsu Bunsuku, Dr Sugimoto Asao, Dr. Yukawa and Dr. Kobayashi. Heavy water was harvested by two heavy water plants, one in Kyushu and another at Noguchi's JNFC-Nitchitsu Fertiliser factory in Korea. Heavy water was harvested as a by-product of Amonia Production for explosives. Noguchi is now a company known by the name Shoji Kamata. Heavy water was used by F-Go in a nuclear reactor project about which there is little publicly available evidence, except post war claims by Prof. Arakatsu.
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It is not known whether Japan's reactor built at Kyoto worked successfully, or managed to breed any Plutonium. All wartime archives are now controlled by the Japanese Government which is under no obligation to disclose them.
An interesting point emerges however that A.H Compton's investigation report for the Manhattan Project notes that Japan made far more progress in the field of developing nuclear energy than Germany did. [11]