What was the proposed Allied invasion plan for Japan that surrender made unnecessary in 1945?

Operation Downfall was the proposed Allied invasion plan for Japan that surrender made unnecessary in 1945.

Downfall was designed as a two-part invasion of the Japanese home islands. Operation Olympic was scheduled to attack southern Kyūshū in November 1945, while Operation Coronet was planned for the Kantō Plain near Tokyo in spring 1946. Japan’s surrender canceled the entire operation before it began.

The plan reflected Allied expectations that Japan might continue fighting despite blockade, bombing, and military defeat. Its planners included major American commanders such as Chester Nimitz and Douglas MacArthur. The proposed invasion would have required enormous forces and was expected to cause very heavy casualties on both sides.

Operation Downfall is often confused with its component operations. Olympic and Coronet were not separate completed invasions; they were the two planned phases of Downfall. Operation Ketsugō was the Japanese defensive plan prepared to oppose an Allied invasion of the home islands.