Operation Downfall is the overall code name for the proposed U.S. invasion of Japan in
World War II. It would have been the largest amphibious operation in history. In the first phase (Operation Olympic), some 250,000 army troops and 87,600 marines would have assaulted Kyushu, the southernmost of Japan's home islands, in November 1945. They were to take the southern half of Kyushu, where air bases would be built for the invasion (Operation Coronet) of Honshu in March 1946. Most of the troops for that invasion would have been U.S. veterans of European fighting.
The planned invasion had historical significance, because President Harry S. Truman weighed the projected high casualty cost of the invasion against the use of the atomic bomb. General of the Army
Douglas MacArthur, who would have commanded ground forces for Downfall, initially estimated that battlefield casualties for the first ninety days of the Kyushu assault would total 95,050. Later he said that a Soviet invasion of Manchuria would greatly lessen casualties because so many Japanese troops would be unable to be deployed from the Asian mainland to the home islands.
By August 1945 Japanese had at least 370,000 ground troops and 575,000 home-defense forces on Kyushu, with defenders massed at the three beaches where U.S. troops would land. President Truman later said that he had been told an invasion "would cost at a minimum one-quarter of a million casualties." Critics of Truman's decision to drop the atomic bomb claimed he had inflated casualty estimates to justify his decision. But U.S. casualties undoubtedly would have been extremely high, especially because of the Japanese "Decisive Battle" strategy: kill so many Americans that the war-weary United States would negotiate a peace. The strategy would be carried out by more than two million troops on the home islands and thousands of kamikaze attacks on troop-filled transports. Japanese troop strength on Kyushu eventually rivaled the size of the invaders' forces, which, as an intelligence report to MacArthur said, "is not the recipe for victory."
Thomas B. Allen
