On May 25, 1945, the Joint Chiefs of Staff met in Washington to approve plans for invading Japan. The invasion, code named "Downfall," would be in two stages. The first, Operation Olympic, would take place on the southern island of Kyushu on November 1. Phase two, Operation Coronet, would use Kyushu as a staging area for the invasion of the Tokyo plain in March 1946.
A Quick End to the War
The chief advocate of the invasion was the Army's chief of staff, General George C. Marshall. He believed that democracies could not endure long wars, and that the best way to end this one quickly was to occupy the Japanese capital.
By the Book
The initial American intelligence estimate predicted that Kyushu would be defended by six divisions. U.S. planners anticipated that the Japanese would be uncertain where the landing would occur and would spread their forces thin -- three divisions in the north, three in the south. The invasion on Kyushu's southern beaches would consist of nine divisions. This three-to-one ratio of invader to defender was the textbook recipe for a successful invasion. The U.S. held another three divisions in reserve.
Death Weighs In
The unprecedented American losses on Okinawa -- one third of the invasion force was killed, wounded or missing -- heightened President Harry Truman's concern about what it would cost in American lives to defeat Japan. He informed the Joint Chiefs of Staff that casualties would be his criterion for authorizing an invasion of the Japanese homeland, a decision he would describe as his hardest up to that point.
Predicting Casualty Numbers
Truman met with the Joint Chiefs and other senior advisers in June 1945 to review the initial invasion plans. At least four different opinions emerged about potential casualties. These estimates for U.S. losses on Kyushu ranged from as low as 31,000 for just the first thirty days, to a total of about 280,000. Truman authorized the landing on Kyushu, but withheld his approval for Coronet.
The Japanese Intended to Fight
American fears about casualty levels were sent soaring in July by intercepts of Japanese military cables. The new intelligence revealed a massive build-up of Japanese forces in southern Kyushu. Historian Edward Drea describes the situation: "It was as if the very invasion beaches were magnets, drawing the Japanese forces to those places where the Americans would have to land and fight their way ashore. It was also very clear in those messages that the Japanese intended to fight to the bitter end."
A New Weapon
Also in July, American military leaders reported successful tests of a devastating new weapon -- the atomic bomb. According to historian Barton Bernstein, the president's advisers focused on "not the issue of use, which... was rather assumed, but rather postwar implications, the power of the bomb... and what it would mean for the world." The bomb's availability would become a factor in the invasion plan, although military planning scenarios never assumed atomic weapons would end the war.
In early August the intercepts indicated 13 Japanese divisions defending the invasion beaches. One intelligence officer noted that the U.S would be attacking on a ratio of one-to-one -- "not the recipe for victory." A deeply worried General Marshall asked General Douglas MacArthur, who was to lead the Kyushu landing, whether it was still feasible, and if not to consider alternatives, including landing troops in northern Japan.
At the same time, General Marshall considered another option to make the Kyushu invasion work. He found out that at least seven atomic bombs would be ready by November 1. On August 6, the U.S. destroyed Hiroshima with an atomic bomb, yet Japan did not surrender. Marshall doubted if bombing cities would force the war to end, and began to consider using atomic bombs to soften up the invasion beaches -- almost as if they were naval gunfire. Planners did not fully comprehend or take into account the lingering, deadly effects of atomic radiation. We know today that, had the invasion taken place under cover of atomic weapons, Japanese defenders who did not die instantly from the bomb blasts would have died a lingering death from radiation poisoning. So would have many American invaders.
After the Soviet Union shocked Japan on August 8th by declaring war, and the U.S. dropped a second atomic bomb on Nagasaki the following day, Japan came to understand it should surrender. There was no need for an invasion after all. But a major legacy of the war's end would be the debate over whether dropping atomic bombs on Hiroshima and Nagasaki saved lives by ending the war sooner. In a postwar article, Secretary of War Henry Stimson would argue that using the atomic bombs saved a million American casualties that might have resulted from an invasion.
Historians today -- like the military planners of the 1940s -- disagree about how many Americans might have died in an invasion. Counting up projected invasion casualties has become important to people seeking to understand why Truman and his cabinet dropped two atomic bombs on Japan. But, as Bernstein points out, "This is really a post-Hiroshima analysis, growing with more fervor as the distance from Hiroshima grows, about the moral legitimacy and the moral justifications for the act, and not about understanding the decision-making leading to the act."
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