Operation Downfall was the Allied invasion plan for Japan that would have followed if Japan had not surrendered in 1945.
The plan was the proposed invasion of the Japanese home islands. It had two major stages: Operation Olympic, the planned invasion of southern Kyushu, and Operation Coronet, the proposed attack on the Tokyo Plain. Olympic was scheduled for November 1945, while Coronet was planned for March 1946.
Allied planners expected fierce resistance because Japanese forces were preparing for a decisive defense of the homeland. Civilian mobilization, fortified positions, kamikaze attacks, and difficult terrain all contributed to estimates of potentially enormous casualties.
The plan was never carried out. Japan announced its acceptance of the Potsdam Declaration in August 1945, after the atomic bombings, the Soviet declaration of war, and political decisions by Japan’s leadership. The cancellation of Downfall meant that the planned invasion of the home islands did not occur.