What was the proposed Allied invasion plan for Japan called if surrender had not occurred?

The proposed Allied invasion plan for Japan was called Operation Downfall.

Operation Downfall was the planned invasion of the Japanese home islands if Japan did not surrender. It had two major components: Operation Olympic, aimed at southern Kyushu, and Operation Coronet, aimed at the Kanto Plain near Tokyo.

Olympic was planned for November 1945, while Coronet was expected in spring 1946. The operation would have required enormous Allied forces and involved anticipated casualties on a potentially massive scale, although estimates varied widely.

Downfall was never carried out. Japan’s surrender followed the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the Soviet offensive in Manchuria. Once Japan accepted surrender terms, the invasion plan was canceled.

Operation Downfall is often confused with its two component operations. Overlord was the Allied invasion of Normandy in 1944, while Olympic and Coronet were the proposed landings within Downfall.