Japanese Nuclear Weapon Program - World War II

World War II

The leading figure in the Japanese atomic program was Dr. Yoshio Nishina, a close associate of Niels Bohr and a contemporary of Albert Einstein. Nishina had co-authored the Klein-Nishina Formula. Nishina had established his own Nuclear Research Laboratory to study high-energy physics in 1931 at Riken Institute (the Institute for Physical and Chemical Research), which had been established in 1917 in Tokyo to promote basic research. Nishina had built his first 26-inch (660 mm) cyclotron in 1936, and another 60-inch (1,500 mm), 220-ton cyclotron in 1937. In 1938 Japan also purchased a cyclotron from the University of California, Berkeley.

In 1939 Nishina recognized the military potential of nuclear fission, and was worried that the Americans were working on a nuclear weapon which might be used against Japan. Indeed, in 1939, President Franklin D. Roosevelt started the first investigations into fission weapons in the United States, which eventually evolved into the massive Manhattan Project, and the laboratory from which Japan purchased its own cyclotron would become one of the major sites for weapons research.

In the early summer of 1940 Nishina met Lieutenant-General Takeo Yasuda on a train. Yasuda was at the time director of the Army Aeronautical Department's Technical Research Institute. Nishina told Yasuda about the possibility of building nuclear weapons. However, the Japanese fission project did not formally begin until April 1941 when Yasuda acted on Army Minister Hideki Tojo's order to investigate the possibilities of nuclear weapons. Yasuda passed the order down the chain of command to Okochi Masatoshi, director of the Riken Institute, who in turn passed it to Nishina, whose Nuclear Research Laboratory by 1941 had over 100 researchers.

Meanwhile, the Imperial Japanese Navy's Technology Research Institute had been pursuing its own separate investigations, and had engaged professors from the Imperial University, Tokyo, for advice on nuclear weapons. This resulted in the formation of the Committee on Research in the Application of Nuclear Physics, chaired by Nishina, that met ten times between July 1942 and March 1943. It concluded in a report that while an atomic bomb was, in principle, feasible, "it would probably be difficult even for the United States to realize the application of atomic power during the war". This caused the Navy to lose interest and to concentrate instead on research into radar.