What was the overall Allied code name for the planned invasion of Japan’s home islands?

Operation Downfall was the overall Allied code name for the planned invasion of Japan’s home islands.

The plan had two major stages. Operation Olympic was intended to land on southern Kyushu in November 1945. Operation Coronet was planned for March 1946 and would have targeted the Kantō Plain near Tokyo on Honshu. Downfall therefore described the complete invasion concept rather than one landing.

American planners expected fierce resistance from Japan’s military and civilian population. They prepared large forces, naval support, air power, and supplies for an operation that could have produced enormous casualties on both sides. The plan was developed while Allied forces continued fighting toward Japan’s surrender.

Downfall was never carried out. Japan accepted the Potsdam Declaration after the atomic bombings, the Soviet declaration of war, and internal political decisions by the Japanese leadership. Olympic and Coronet were consequently canceled, and the Allies instead began the occupation of Japan in late August 1945.