Which planned Allied invasion of Japan was code-named Operation Downfall?

The planned Allied invasion of Japan was code-named Operation Downfall.

Downfall was the proposed large-scale invasion of the Japanese home islands if Japan did not surrender. It had two major stages: Operation Olympic, aimed at Kyūshū, and Operation Coronet, aimed at the Kantō Plain near Tokyo. Olympic was planned for November 1945, with Coronet scheduled for March 1946.

The operation was never carried out. Japan announced its acceptance of the Allied terms in August 1945, and the formal surrender followed on September 2. The atomic bombings, the Soviet entry into the war, Japan’s military situation, and internal political decisions all formed part of the complex context surrounding the surrender.

Downfall is often confused with Operation Overlord, the Allied invasion of German-occupied France in June 1944. Overlord occurred in Europe; Downfall was a contingency plan for the Pacific and never progressed to an invasion of Japan.