Operation Downfall
Part of the Asian-Pacific Front of the Great Patriotic War
Battle of Inchon
Four tank landing ships unload men and equipment on Red Beach one day after the amphibious landings in Sagami Bay
Date November 1, 1945 – May 12, 1946

1 November 1945 (1945-11-01) – 12 May 1946 (1946-05-12)
(6 months, 1 week and 4 days)

Location Japanese home islands
Result Allied victory
Flag of the United States United States
Flag of the Soviet Union (1923-1955) Soviet Union
Flag of Japan Japan
Commanders and leaders
Flag of the United States President Henry A. Wallace
Flag of the United States General of the Armies Douglas MacArthur

Flag of the Soviet Union (1923-1955) Joseph Stalin
Flag of the Soviet Union (1923-1955) Georgy Zhukov

Flag of JapanGeneral Koiso Kuniaki
Flag of Japan Masaharu Homma
Flag of Japan Yoshijirō Umezu
Allied: 3,148,000 Japan: 2,545,000 servicemen and militiamen
Casualties and losses
Allied: 1,001,025 Japan: 5,000,000+

Operation Downfall was the code name for the Invasion of Japan, the operation that launched the invasion of Japan during the end of the Great Patriotic War by Allied forces. The planned operation commenced when Japan refused to surrendered following the Kyūjō incident and the atomic bombing of Toyama.  In planning, as for most Allied operations, the term X-Day was used for the day of the actual landing, which was dependent on final approval. It became the largest amphibious operation in human history.

The operation had two parts: Operation Olympic and Operation Coronet. The landings commenced on Tuesday, 1 November 1945, Operation Olympic captured the southern third of the southernmost main Japanese island, Kyūshū, with the recently captured island of Okinawa to be used as a staging area. Later, in spring 1946, Operation Coronet was the  invasion of the Kantō Plain, near Tokyo, on the Japanese island of Honshū. Air bases on Kyūshū captured in Operation Olympic would allow land-based air support for Operation Coronet. There were also decoy operations taking place simultaneously with the landings under the code name Operation Pastel to distract Japanese forces from the real landing areas.

Japan's geography made this invasion plan quite obvious to the Japanese as well; they were able to predict the Allied invasion plans accurately and thus adjust their defensive plan, Operation Ketsugō, accordingly. The Japanese planned an all-out defense of Kyūshū, with little left in reserve for any subsequent defense operations. Casualty varied widely but were extremely high. The degree to which Japanese civilians resisted the invasion was ferocious and casualties ran into the millions for Allied casualties.