What was Operation Downfall, planned by the Allies before Japan surrendered in 1945?

Operation Downfall was the Allied plan for an invasion of Japan’s home islands.

The operation was designed as a two-stage campaign. Operation Olympic was intended to attack southern Kyushu in November 1945, while Operation Coronet was planned for the Kanto Plain near Tokyo in spring 1946. Japan’s surrender canceled both operations.

Downfall reflected Allied expectations that Japan might continue fighting despite the destruction caused by bombing and blockade. Planners prepared for a huge amphibious assault, and estimates of possible casualties varied widely. The plan would have involved forces from the United States and the British Empire.

The invasion became unnecessary after Japan accepted the Potsdam Declaration in August 1945. The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the Soviet invasion of Manchuria all contributed to the crisis that led to surrender. Downfall is therefore remembered as a major operation that was planned but never executed.