What was the name of the Allied plan for invading Japan if it refused to surrender in 1945?

Operation Downfall was the Allied plan for invading Japan if it refused to surrender in 1945.

The plan was designed as a massive two-stage invasion of the Japanese home islands. Operation Olympic would have attacked southern Kyūshū, while Operation Coronet would have followed with an assault on the Kantō Plain near Tokyo. Olympic was planned for November 1945, and Coronet for March 1946.

Downfall was never carried out because Japan accepted the Allied terms in August 1945. The atomic bombings of Hiroshima and Nagasaki, the Soviet entry into the war, Japan’s internal political crisis, and the emperor’s intervention all preceded the surrender announcement.

The plan is sometimes confused with its component operations. Downfall was the overall invasion plan; Olympic and Coronet were its two major phases. Estimates of the possible casualties varied widely, and later claims about what the invasion would have cost remain contested because the operation never occurred.