What was the Allied plan for invading Japan’s main islands in 1945 called?

The Allied plan for invading Japan’s main islands was called Operation Downfall.

Downfall was a proposed two-stage invasion planned for late 1945 and 1946. Operation Olympic would have landed Allied forces on Kyushu in November 1945, while Operation Coronet would have targeted the Kantō Plain near Tokyo in March 1946.

The invasion was never carried out because Japan surrendered in August 1945 and signed the formal surrender instrument in September. Allied planners nevertheless prepared extensively, expecting fierce resistance from Japanese troops and civilians. Estimates of likely casualties varied widely and remain debated by historians.

Operation Downfall is often confused with Operation Olympic, which was only the first phase of the larger plan. It is also distinct from Operation Overlord, the Allied invasion of Normandy in June 1944. The planned invasion helps explain why the Japanese surrender dramatically changed the closing weeks of the war.