What was the U.S. military plan for invading Japan’s home islands if Japan did not surrender in 1945?

Operation Downfall was the U.S. military plan for invading Japan’s home islands in 1945.

The proposed operation had two major stages. Operation Olympic would have attacked Kyushu, the southernmost of Japan’s four main islands, on November 1, 1945. Operation Coronet was planned for Honshu, near Tokyo, on March 1, 1946. Together they formed Operation Downfall.

The plan was never carried out because Japan surrendered in August and signed the formal instrument in September. Allied planners expected severe resistance from Japanese forces and civilians, and preparations included estimates of potentially enormous casualties. The planned invasion is often discussed when explaining why American leaders considered alternatives to continued conventional warfare.

Operation Downfall should not be confused with Operation Overlord, the Allied invasion of Normandy in June 1944. Downfall was a contingency plan for Japan, not a completed battle. Its cancellation also meant that the planned landings, occupation zones, and expected fighting on the home islands never occurred.