Command and Control

The ideal target of the atomic bomb would be a large city that had not yet been firebombed, so the effects of the new weapon could be reliably assessed. The first four choices of the president’s Target Committee were Kyoto, Hiroshima, Yokohama, and Kokura. Secretary of War Henry Stimson insisted that Kyoto be removed from the list, arguing that the city had played too central a role in Japanese art, history, and culture to be wiped out. Nagasaki took its place. The day after the Trinity test, Szilárd and more than sixty-eight other Manhattan Project scientists signed a petition, addressed to the president. It warned that using the atomic bomb against Japan would open the door “to an era of devastation on an unimaginable scale” and place American cities in “continuous danger of sudden annihilation.” The petition never reached the president. And even if it had, it probably wouldn’t have changed his mind.

Franklin Roosevelt had never told his vice president, Harry Truman, about the Manhattan Project or the unusual weapon that it was developing. When Roosevelt died unexpectedly, on April 12, 1945, Truman had the thankless task of replacing a beloved and charismatic leader during wartime. The new president was unlikely to reverse a nuclear policy set in motion years earlier, at enormous expense, because a group of relatively unknown scientists now considered it a bad idea. Truman’s decision to use the atomic bomb was influenced by many factors, and the desire to save American lives ranked near the top. An invasion of Japan was scheduled for November 1. Former President Herbert Hoover warned Truman that such an invasion would cost between “500,000 and 1,000,000 American lives.” At the War Department, it was widely assumed that American casualties would reach half a million. During the recent battle of Okinawa, more than one third of the American landing force had been killed or wounded — and a full-scale invasion of Japan might require 1.8 million American troops. While meeting with the Joint Chiefs of Staff in June 1945, Truman expressed the hope of avoiding “an Okinawa from one end of Japan to the other.”

Unlike most presidents, Truman had firsthand experience of battle. During the First World War, half of the men in his infantry division were killed or wounded during the Meuse-Argonne offensive. Standing amid piles of dead American soldiers, the sergeant of his platoon had yelled at the survivors: “Now… you’ll believe you’re in a war.” Truman took no pleasure in the deaths of Japanese civilians. But he preferred them to the deaths of young American servicemen. Atomic bombs, he decided, would be dropped on Japan as soon as they were ready.

The Trinity test had been preceded by weeks of careful preparation, and every effort had been made to control the outcome. The device had been slowly and patiently assembled. The wiring and explosives had been repeatedly checked. The tower had been built, the location of the test chosen, and each step of the countdown arranged as part of an elaborate, scientific experiment. Turning an experimental device into an operable weapon presented a new set of challenges. Atomic bombs had to be dropped, somehow, and American aircrews had to survive the detonations. B-29 bombers were secretly retrofitted so that nuclear weapons would fit inside them. And pilots were secretly recruited to fly these “Silverplate” B-29s. They practiced dropping dummy bombs, then banking steeply to escape the blast. Enough fissile material for two nuclear weapons — a gun-type device loaded with uranium-235 and an implosion device with a plutonium core — were readied for use against Japan. The arming and fuzing mechanisms of the bombs would determine when they exploded, whether they exploded, and how much time the bomber crews would have to get as far away as possible.