What code name did the Allies give their planned invasion of Japan?

Operation Downfall was the Allied code name for the planned invasion of Japan.

Downfall was the proposed campaign to defeat Japan through a direct invasion of the Japanese home islands. It consisted of two planned stages: Operation Olympic, an invasion of Kyushu scheduled for November 1945, and Operation Coronet, an assault on Honshu near Tokyo planned for March 1946.

The invasion was never carried out. Japan’s surrender in August 1945 followed the atomic bombings of Hiroshima and Nagasaki, the Soviet entry into the war against Japan, and the Japanese leadership’s decision to accept the Potsdam terms. The cancellation avoided the enormous casualties that planners expected from an invasion.

Operation Downfall is often confused with Operation Overlord, the code name for the Allied invasion of Normandy in June 1944. Olympic and Coronet were components of Downfall, not alternative names for the entire plan. The projected invasion influenced Allied military planning even though its first landings never occurred.