Operation Downfall — codename for the Allied plan for the invasion of Japan near the end of World War II
Operation Downfall, had it occurred, would have been the largest amphibious invasion in history, potentially causing millions of casualties on both sides.
Key Facts
- Planned start date
- November 1945 (Operation Olympic)
- Second phase
- Operation Coronet, Spring 1946, Kantō Plain
- Staging area
- Okinawa, for Olympic; Kyūshū for Coronet
- Allied casualty estimates
- Low hundreds of thousands to over one million
- Japanese casualty estimates
- Into the millions
- Reason for cancellation
- Japan surrendered after atomic bombings and Soviet war declaration
Location
Cause → Event → Consequence
As World War II neared its end in the Pacific, Allied planners determined that Japan would not surrender without a direct invasion of its home islands. With Okinawa secured as a staging area, the United States and British Empire developed Operation Downfall to force Japan's capitulation through overwhelming amphibious assault.
Operation Downfall was structured in two phases: Operation Olympic, targeting the southern third of Kyūshū in November 1945, and Operation Coronet, targeting the Kantō Plain near Tokyo in Spring 1946. Japan anticipated the invasion and prepared Operation Ketsugō, concentrating defenses on Kyūshū. Casualty projections on both sides reached into the millions, making it potentially the most costly amphibious operation in history.
Operation Downfall was never executed. Japan surrendered in August 1945 following the atomic bombings of Hiroshima and Nagasaki and the Soviet Union's declaration of war and invasion of Manchuria. The cancellation spared both sides the catastrophic casualties projected and brought World War II to a close without a land invasion of the Japanese home islands.
Belligerents & Mobilization Analysis
Side A
2 belligerents
Side B
1 belligerent