What was the Allied operation name for a planned invasion of Japan’s home islands?

The planned Allied invasion of Japan’s home islands was called Operation Downfall.

Operation Downfall was the broad American plan for invading Japan if its government did not surrender. It had two main stages: Operation Olympic, the proposed invasion of Kyushu, and Operation Coronet, the proposed invasion of Honshu near Tokyo. Olympic was scheduled for November 1945, while Coronet was planned for March 1946.

The invasion never occurred because Japan accepted the Allied surrender terms in August 1945. The atomic bombings of Hiroshima and Nagasaki, the Soviet entry into the war against Japan, and political decisions by Japan’s leaders all shaped that outcome.

Operation Downfall is sometimes confused with Operation Overlord, the Allied invasion of Normandy in June 1944. Overlord concerned the European theater; Downfall was the unexecuted plan for the final campaign against Japan.