Abstract
A plan of plutonium bomb was existed separately from a plan of uranium bomb at the beginning of the development of atomic bombs. The following is the transition of significance of the plan of plutonium bomb.
In December 1940, the plan of plutonium bomb was posed in England and U.S.A. independently.
In December 1941, the plan of plutonium bomb was not stated clearly, but it was interested in whether the fission chain reaction using uranium is feasible or not. Because, such reactions will produce the "94" (plutonium) which is material of plutonium bomb.
In June 1942, the plan of plutonium bomb was stated clearly, and also it caused Army and Industries to be concerned in the development of atomic bomb in earnest.
In December 1942, the chain reaction was proved. So the plan of plutonium bomb was changed from which to be for ending the war to which to be concerned with the atomic power policy of the post war.
