Operation Downfall was the overall Allied invasion plan for Japan’s home islands that was canceled after Japan surrendered. It was planned for late 1945 and 1946 if Japan continued fighting.
Downfall had two major stages. Operation Olympic was scheduled to land on Kyūshū on 1 November 1945, while Operation Coronet was planned for the Kantō Plain near Tokyo on 1 March 1946. The plan required enormous naval, air, and ground forces and was expected to produce severe casualties.
The invasion never occurred because Japan accepted the Allied terms in August 1945 and formally surrendered in September. The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war on Japan, and the Soviet invasion of Manchuria all formed part of the final strategic crisis surrounding the surrender.
Downfall is sometimes confused with Olympic, but Olympic was only its first phase. It is also not the same operation as Overlord, the Allied invasion of German-occupied France in 1944.