By August, 1945, Japan's main cities and key war industries were already seriously damaged or destroyed from the use of conventional bombs. Japan's harbors were heavily mined, and it could no longer import sufficient food or fuel. A U. S. Strategic Bombing Survey team which went into Japan in 1945 estimated that the Japanese would have surrendered by November 1945 even without an invasion of their homeland.
"It wasn't necessary to hit them with that awful thing."
-- Dwight D. Eisenhower, former U.S. president and
Supreme Allied Commander in Europe during World War II, 1963
"It occurred to me that a quarter of a million of the flower of our young manhood was worth a couple of Japanese cities, and I still think they were, and are."
-- President Truman, late 1945.
President Truman and his top civilian and military advisors thought the war would be ended quickly if the atomic bomb were used. Using the atomic bomb, Truman said, would actually save the lives of more people than were killed at Hiroshima and Nagasaki.
Some military estimates said American forces invading the Japanese mainland could suffer up to a million casualties. U.S. allies would also suffer heavy losses, and Japan would experience even higher losses. While the Japanese Navy and Air Force were virtually destroyed by August 1945, the Japanese Army still had five million men under arms.
According to some scholars, Japan's military leaders did not plan to surrender in 1945. In January 1945, the Emperor approved a strategic plan that called for the defense of the homeland and the "final decisive battle" of the war. This included using thousands of remaining Japanese aircraft in kamikaze raids, where the pilots would crash their planes into American ships in suicide missions.