What Allied invasion plan was prepared in case Japan refused to surrender in 1945?

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

The plan was divided into two major stages. Operation Olympic was scheduled to begin with an invasion of Kyushu, Japan’s southernmost main island, in November 1945. Operation Coronet would then have targeted the Kanto Plain near Tokyo in March 1946. Together, these operations formed Operation Downfall.

The plan required enormous forces and anticipated fierce resistance. Japanese military leaders prepared defensive measures under Operation Ketsugo, mobilizing regular troops and civilians for a homeland battle. American planners expected very high casualties, although the exact numbers remain debated by historians.

Japan surrendered before either Olympic or Coronet began. The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, Japan’s military situation, and internal political decisions all contributed to the final outcome. Because the invasion was never launched, Downfall remains a major example of a large military operation that existed only as a plan.

Operation Downfall is often confused with Operation Olympic, but Olympic was only its first stage.