What was the Allied plan code-named for a full-scale invasion of Japan’s home islands in 1945?

Operation Downfall was the Allied plan for a full-scale invasion of Japan’s home islands in 1945.

The proposed operation had two major stages. Operation Olympic would attack southern Kyushu in November 1945, while Operation Coronet would follow with an invasion of the Kanto Plain near Tokyo in spring 1946. The plan was canceled after Japan accepted surrender terms.

Downfall was expected to require enormous forces and could have caused severe casualties on both sides. Allied planners prepared for fierce resistance because Japan had mobilized military units and civilians for homeland defense. The estimates varied widely, and no invasion of the main Japanese islands actually took place.

The plan is often confused with Operation Overlord, the Allied invasion of Normandy in June 1944. It is also distinct from Operation Ketsugō, Japan’s defensive plan for resisting an Allied invasion. The atomic bombings and Soviet offensive made Downfall unnecessary.