What was the Allied invasion plan for Japan called if Japan refused to surrender in 1945?

The planned Allied invasion of Japan was called Operation Downfall. It was prepared for use if Japan did not surrender, but the operation was never carried out because Japan accepted the Allied terms in August 1945.

Downfall was divided into two major phases. Operation Olympic was scheduled as the first phase and would have targeted southern Kyūshū. Operation Coronet was planned as the second phase and would have attacked the Kantō Plain near Tokyo on Honshū. The projected invasion involved enormous Allied forces and uncertain casualties.

Planning for Downfall reflected the expectation that Japan might continue resisting after years of intense fighting. Japanese military leaders were also preparing defensive plans for a possible invasion of the home islands. The atomic bombings, the Soviet declaration of war, and political developments inside Japan changed the situation before the invasion began.

Operation Downfall is often confused with Operation Overlord, the Allied invasion of German-occupied France in 1944. Olympic and Coronet were components of Downfall, while Overlord belonged to the European theater. No Allied troops landed on Japan’s main islands as part of Downfall.