Operation Downfall was the codename for the Allied plan for the invasion of Japan near the end of World War II. The planned operation was abandoned when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki and the Soviet declaration of war. The operation had two parts: Operations Olympic and Coronet. Set to begin in October 1945, Operation Olympic was intended to capture the southern third of the southernmost main Japanese island, Kyushu, with the recently captured island of Okinawa to be used as a staging area. Later, in spring 1946, Operation Coronet was the planned invasion of the Kanto Plain, near Tokyo, on the Japanese island of Honshu. Airbases on Kyushu captured in Operation Olympic would allow land-based air support for Operation Coronet. If Downfall had taken place, it would have been the largest amphibious operation in history.