What was the Allied plan for invading Japan's home islands if Japan had not surrendered in 1945?

Operation Downfall was the Allied plan for invading Japan's home islands if Japan had not surrendered in 1945.

The proposed operation had two major stages. Operation Olympic was intended to land on southern Kyushu in November 1945, while Operation Coronet was planned for the Kanto Plain near Tokyo in spring 1946. Together, they would have created the largest amphibious operation in history.

Japanese planners anticipated an invasion and developed Operation Ketsugo to defend the home islands. Allied casualty estimates varied widely, and the expected cost of an invasion was a major factor in wartime planning and later historical debate.

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 Emperor's decision to accept the Allied terms.