16. The atomic bomb accelerated invasion planning
The first atomic bomb was dropped over Hiroshima on August 6, 1945. Even before the second bombing at Nagasaki on August 9, invasion planners were incorporating the use of the bomb as part of Operation Downfall. The Joint Chiefs had begun adding atomic weapons to the plans following the successful Trinity test of the device in July. George Marshal requested a report on the number of weapons that would be available by November 1 and a recommendation regarding their use on Japanese troop concentrations in Kyushu. The report was requested because the Americans had begun to notice the concentration of Japanese assets in the invasion areas.
Nimitz and King, also concerned by the apparent increases in Japanese aircraft strength and assuming they were to be used as kamikaze weapons, recommended bypassing the Kyushu phase of Operation Downfall and concentrating on one of the northern islands. King was for canceling the invasion altogether. MacArthur was unconcerned with the reports of Japanese strength and recommended moving the invasion date up. “I am certain that the Japanese air potential reported to you as accumulating to counter our Olympic operation is greatly exaggerated,” he wrote to Marshall. MacArthur also discounted the reports of Japanese troop strength and continued to urge invasion.