Why Did We Drop the Bomb?

By Walter lsaacson

The ceremonies marking the 40th anniversary of Hiroshima's obliteration are over, and the ghostly figures of vaporized corpses that were stenciled on the sidewalks of scores of American cities have already begun to fade. What remains is a question, the same one that has gnawed at us from the first: Did the U.S. really have to drop the atomic bomb?

Harry Truman, the man who gave the order, explained often and emphatically that he did so for the simplest yet most compelling of reasons: to end the war. Such surety seems comforting. Yet one thing last week's observances showed is that such a simple explanation remains unsettling. We continue to poke through the rubble of history, compelled to search for clues about why something so incomprehensible can seem so explainable.

There were without doubt persuasive military reasons for using the new weapon in the summer of 1945. The first day of fighting on Iwo Jima had cost more American casualties than D-day; on Okinawa, 79,000 U.S. soldiers were killed or wounded. As the U.S. readied plans to invade the main islands, Japan was deploying up to 2 million soldiers and additional millions of "auxiliaries" who were clearly prepared to defend their homeland to the death. It was easy to believe estimates that an invasion would result in as many as a million American casualties, plus many more Japanese. The Bomb offered the chance of ending the war and saving lives.

In addition, the Bomb, like any new weapon, had developed a constituency and a momentum of its own. J. Robert Oppenheimer, the charismatic master of Los Alamos, gave short shrift to those scientists working under him who urged that their creation not be used. Congressional committees, the first of them led by a Missouri Senator named Truman, had long been grumbling about the huge secret appropriations poured into the Manhattan Project and warning that the results had better be worth the $2 billion investment, which was serious money in those days. When the scientists succeeded, it became all but impossible to argue that their weapon, one that could prevent a bloody invasion, should be shelved.

There was, however, another factor, one still enmeshed in historical controversy. By the end of July, Japan was reeling. It was likely that a Soviet declaration of war would be the coup de grace. Gar Alperovitz, a historical revisionist whose newly updated Atomic Diplomacy is a harsh critique of American policy, argues that Truman was well aware of this. One of his principal goals during the Big Three meeting in the Berlin suburb of Potsdam in July 1945 was to secure Stalin's pledge to enter the war within a few weeks. When the Soviet dictator agreed, Truman jotted in his diary: "Fini Japs when that comes about."

American officials, however, were already having second thoughts about entering into another partnership with the Soviets. Stalin was, to say the least, a troublesome ally in the occupation of liberated Europe. When news of the successful Alamogordo test reached Potsdam, top American officials began to view the Bomb as a way to avoid the need for Soviet involvement in the Pacific war, rather than viewing Soviet involvement as a way to avoid the need for the Bomb. Secretary of State James Byrnes, Truman's closest confidant on atomic matters, was eager to "get the Japanese affair over before the Russians got in" and felt that knowledge of America's new weapon would make the Soviets "more manageable." Secretary of War Henry Stimson, perhaps the most respected U.S. statesman of the century, was wary of using the Bomb as a diplomatic bludgeon, but even he referred to it as a "master card" in Washington's dealings with the Kremlin.

Ways to avoid dropping the Bomb were never really a matter of discussion. At one White House meeting in June, Stimson's assistant John McCloy suggested that Japan be issued a warning about the weapon and offered surrender terms that allowed the retention of the Emperor. McCloy's goal, however, was not so much to prevent the Bomb from being dropped as to avoid the need for the invasion being planned at the meeting. The secrecy surrounding the device known as S-1 was so pervasive that a hush quickly fell over the room and exploration of the options was inhibited. When Japan was issued a warning from Potsdam a month later, no explicit mention was made of either the Bomb or the Emperor. Radio Tokyo broadcast that the Japanese government would treat the warning with "silent contempt." On the island of Tinian that day, a 300-lb. lead cylinder with a core of enriched uranium was being transferred to the headquarters of Colonel Paul Tibbets' 509th Composite Group.

Perhaps the crucial factor in the decision to proceed with the atomic bombing was that none of America's leaders felt any urgency about finding a way to avoid it. The scientists had not stressed that their creation might unleash radioactive fallout that would make the Bomb a more sinister weapon than even chemical warfare. Truman and his advisers knew that the explosion would be phenomenally large, but considered it no more morally repulsive than the massive fire-bombing raids that had cremated much of Tokyo. Stimson, the man who wrestled most with these imponderables, called the Bomb "the most terrible weapon ever known," but even he considered it "as legitimate as any other of the deadly explosive weapons of modern war."

The decision, then, was from their vantage simple. If Truman had not used the Bomb, how could he have explained it to the families of the boys who would subsequently have died, be it 40,000 of them or a million? How could he have justified continuing the war, transferring weary G.I.s to the Pacific to prepare for an invasion, proceeding with the grotesque fire bombings and allowing the Kremlin to expand its grip in the Far East when he had spent $2 billion on a weapon that could produce a quick end to the conflict?

What makes the subject disquieting, however, is not that the decision seems so baffling but that it seems so explainable. Most Americans are convinced that their nation is among history's most moral. Yet a combination of factors, most of them justified and all of them understandable, created a momentum for unleashing a truly monstrous force. Will future historians someday find themselves sorting through the rubble of another atomic attack, by a nation as moral or one that is less so, and come to the same frightening conclusion? It would be far more comforting to think that the dropping of the Bomb made global war simply unthinkable, something that could never happen again. --By Walter Isaacson