What was the Allied invasion plan for Japan that was prepared before Japan surrendered in 1945?

Operation Downfall was the Allied invasion plan for Japan prepared before Japan surrendered in 1945.

The plan was divided into two major stages. Operation Olympic called for an invasion of southern Kyūshū, while Operation Coronet was intended to attack the Kantō Plain near Tokyo. Olympic was scheduled for November 1945, with Coronet planned for March 1946.

Downfall was never carried out because Japan accepted the Allied surrender terms in August and formally signed the surrender instrument in September. The atomic bombings, the Soviet entry into the war, Japan’s internal political crisis, and the emperor’s intervention all formed part of the final sequence leading to surrender.

Operation Downfall is sometimes confused with Olympic or Coronet. Those were component operations within the larger invasion plan. The plan also differs from Operation Detachment, the earlier American operation for the Battle of Iwo Jima.