Operation Downfall was the Allied invasion plan for Japan that was abandoned after Japan surrendered in 1945.
The plan covered a proposed two-stage invasion of the Japanese home islands. Operation Olympic would have landed Allied forces on Kyushu in November 1945, while Operation Coronet was planned for the Kanto Plain near Tokyo in March 1946. Together, those operations made up Operation Downfall.
Allied planners expected extremely heavy fighting because Japan was preparing military units and civilians for resistance. The invasion plans included large numbers of U.S. troops, naval forces, aircraft, and support personnel. Casualty estimates varied widely and were debated by American officials, historians, and later commentators.
Operation Downfall never took place. Japan’s acceptance of the Potsdam Declaration, following the atomic bombings and the Soviet entry into the war, led to the surrender announcement in August and the formal signing in September. Olympic and Coronet were therefore canceled. The name is sometimes mistakenly used for only the Kyushu landing, but Downfall properly refers to the overall invasion concept.