What was the proposed Allied invasion plan for Japan that was canceled after the 1945 surrender?

Operation Downfall was the proposed Allied invasion plan for Japan that was canceled after Japan surrendered in 1945.

The plan covered a large-scale invasion of the Japanese home islands. Its first stage, Operation Olympic, was intended to land on southern Kyushu in November 1945. The second stage, Operation Coronet, was planned for the Kanto Plain near Tokyo in spring 1946.

Downfall was never carried out. Japan’s surrender followed the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war on Japan, and the Soviet invasion of Japanese-held territory in Manchuria. These events helped produce Japan’s decision to accept the Potsdam Declaration.

If implemented, Downfall would have required an enormous concentration of Allied troops and shipping. Estimates of possible casualties varied widely, which is why claims about a single certain casualty figure should be treated cautiously. The operation’s cancellation prevented the planned invasion from becoming a battlefield.