What planned Allied invasion of Japan was prepared for World War II if Japan did not surrender?

Operation Downfall was the planned Allied invasion of Japan if Japan did not surrender.

The plan had two major stages. Operation Olympic was scheduled to begin with an invasion of southern Kyūshū, while Operation Coronet was intended to follow with an assault on the Kantō Plain near Tokyo. Downfall was the overall plan combining both operations.

Olympic was scheduled for November 1945, and Coronet was planned for March 1946. Allied planners expected fierce resistance because Japanese forces had prepared defenses, civilians were being organized for possible combat, and the battles of Iwo Jima and Okinawa had shown how costly assaults could be.

Operation Downfall was never carried out. Japan’s acceptance of the Allied terms in August 1945 and the formal surrender in September removed the need for the invasion. Operation Overlord, by contrast, was the 1944 Allied invasion of Normandy. Operation Olympic was not the full invasion plan; it was only Downfall’s first major phase.