19. Casualty estimates of an invasion were widely disparate
In May 1945, Admiral Nimitz directed his staff to prepare a casualty estimate based on the known Japanese defenses at the time. His staff estimated 49,000 casualties in the first 30 days of an invasion of Kyushu, including 5,000 at sea. In contrast, MacArthur’s staff estimated less than half the number of casualties in the first 30 days, and a total of 125,000 in four months, at which point the US Army would assume a defensive posture in preparation to support Operation Coronet. MacArthur’s estimate was based on fighting what he claimed was the true number of combat troops on Kyushu, approximately 300,000 men. In fact, there were over 900,000 combat troops present, with more on the way.
In conference with President Truman, George Marshall reported that American casualties would be about 20% of those sustained by the Japanese on Kyushu, which he assumed would be the entire force of 350,000. His estimate was thus 70,000 American casualties. But the real strength of the Japanese force was over 900,000, making American casualties 180,000. Neither MacArthur’s nor Marshall’s estimates included naval casualties. At Okinawa, two thousand kamikazes led to just under 9,000 Navy dead and wounded, with more dead than wounded. The Japanese had ten thousand kamikaze aircraft alone prepared for Operation Olympic, with a large number of suicide weapons on and under the sea as well.