War Stories

Sleepwalking Into the Atomic Age

The decision to bomb Hiroshima wasn’t a decision at all.

Visitors look at a picture showing the aftermath of the atomic bomb attack on Hiroshima at the Hiroshima Peace Memorial Park in Japan in 2005.
Junko Kimura/Getty Images

Seventy-five years ago today, on Aug. 6, 1945, the world erupted into a new era. A single B-29 Superfortress airplane, nicknamed Enola Gay, dropped a new kind of weapon—an atomic bomb—on the Japanese city of Hiroshima. Releasing the blast power of 12,500 tons of TNT, the heat of the sun, and a mushroom cloud of radiation, it obliterated 5 square miles of the city and killed 150,000 people, half of them instantaneously. Along with a second A-bomb dropped on Nagasaki three days later, it forced the Japanese to surrender, ending the Second World War. But it also triggered a nuclear arms race that continues to this day; and while the possession of whole arsenals of these weapons, in the hands of nine nations, may have deterred political leaders from starting a few wars, it is also true that, if these bombs—most of them tens or hundreds of times more powerful than the one dropped on Hiroshima—are ever used in anger again, the consequences could be catastrophic, possibly resulting in a “nuclear winter” that ends most life on Earth.

And so, on the anniversaries of Hiroshima, like some doomsday variant of Passover, we ask the four questions that ethicists and historians have been posing for decades:


• Why did President Harry Truman decide to bomb Hiroshima?

• Why did he then decide to bomb Nagasaki?

• Would a demonstration of the weapon—a massive eyewitnessed explosion in the middle of nowhere—have persuaded the Japanese to surrender?

• How might the war have ended—would more or fewer people have died—if the atom bomb had never been invented?

On the first two questions, declassified archival documents are pretty clear: There never was a decision to drop either bomb. Instead, there was a decision to build an atom bomb. Once it was ready, it was used; once the second bomb was ready, it too was used. From the outset, this was the plan—an automatic sequence from building the bomb to testing it to dropping it on the enemy. The only decision Truman made was not to alter the plan.

The project to build the bomb began with a 1939 letter from Albert Einstein to President Franklin D. Roosevelt, confiding that a fission chain reaction of uranium could produce a very powerful bomb and warning that German scientists were at work on building one for the Nazi government. Two years later, Roosevelt set in motion the Manhattan Project, a top secret, $2 billion enterprise run by the nation’s top physicists and engineers, supervised by Gen. Leslie Groves. By the time they detonated the first bomb at the Trinity test site in New Mexico, on July 16, 1945, the Germans had surrendered. And so, it would be used against the Japanese, who were fiercely fighting on.


Already, by this time, the War Department had created a targeting panel, to decide precisely where to drop the bomb. The minutes of a meeting in May 1945 note that the destruction of the selected target should inflict “the greatest psychological effect against Japan.” By that measure, “Hiroshima has the advantage of being such a size, and with possible focusing from nearby mountains, that a large fraction of the city may be destroyed.”

Scott Sagan, a nuclear scholar at Stanford University, has recently argued that deliberately dropping the bomb on a city, with a prime intention to kill civilians, would be considered a war crime—a violation of the Geneva Convention, which hadn’t yet been signed in 1945. Still, even well before World War II, distinctions had been drawn between civilian and military targets, especially in the context of aerial bombardment, which had started in the First World War.

However, this Rubicon was firmly crossed by the time of Hiroshima. At the start of World War II, Allied air forces pursued a policy of “precision bombing” against the “vital nerve centers” of the German economy. But that meant flying in daylight, in order to see the target, which opened up the bombers to German fighter pilots and anti-aircraft gunners. The Allies started flying at night instead but couldn’t find specific targets, so they made a virtue of necessity and proclaimed that the main target of attack was the “morale” of the German people: It didn’t matter what you hit as long as you hit something. Nearly one-fifth of German houses were destroyed or heavily damaged by Allied bombing, 300,000 civilians were killed, and 780,000 wounded. By the same token, Germany fired its V1 and V2 rockets at the heart of London, under the same rationale.


By the final year of the war, in the Pacific, Gen. Curtis LeMay’s 21st Bomber Command firebombed Tokyo and nearly every other city in Japan. (When the Target Committee decided which cities to hit with A-bombs, they skipped over the remaining cities that LeMay still planned to incinerate.) In March, LeMay amassed 334 B-29s to drop incendiary bombs over Tokyo, killing 84,000 residents. The unique thing about the atom bomb wasn’t that it killed lots of civilians; it was that it did so with stunning efficiency—for, as the targeting panel put it, “the greatest psychological effect.”

In June 1945, a few of the physicists in the Manhattan Project, notably James Franck and Leo Szilard, expressed concerns about what they called “political and social problems” of the bomb—its murderous destructiveness and the possibility of a nuclear arms race after the war—and urged the administration to demonstrate the bomb, on a “desert or barren island,” before using it to kill people. A month later, they and 66 of their colleagues signed a petition to the president, making the same points. However, the top-ranking scientists on the project—including J. Robert Oppenheimer, Ernest Lawrence, Enrico Fermi, and Arthur Compton (who was Franck and Szilard’s immediate supervisor)—disagreed, saying a peaceful demonstration would prolong the war. The top U.S. officials sided with the directors—or, more accurately, took the directors’ reports as affirmation of their own position. President Harry Truman—who hadn’t heard of the Manhattan Project until April, when Roosevelt died and he stepped up from vice president to commander in chief—never saw these petitions, in any case. (After the war, many of these scientists joined or led anti-nuclear organizations. Oppenheimer opposed development of the much more powerful hydrogen bomb and lost his security clearance as a result.)


Before the bombs fell, Truman’s briefers told him that Hiroshima and Nagasaki were military targets. (There was a troop-loading dock on the outskirts of Hiroshima, but this was a minor consideration; the bomb was aimed at the city’s center.) For many years after, Truman feigned total comfort with having dropped the bombs, boasting that he “never lost any sleep” over Hiroshima or Nagasaki. However, the archives reveal that, in fact, he was horrified by the civilian destruction—and even ordered his generals not to drop a third bomb, so he wouldn’t have to kill more of “those kids.” Groves, the Manhattan Project’s supervisor, had been planning to do just that as soon as a third bomb was ready, sometime after Aug. 24, if Japan hadn’t surrendered by then; but Army chief of staff Gen. George Marshall told him not to do so without Truman’s express orders. (Not long after the war, Truman imposed civilian control over atomic weapons, telling his generals, “This isn’t a military weapon”; for a few years, A-bombs were kept separate from the planes that would carry and drop them, under the control of the Atomic Energy Commission, not Strategic Air Command.)

So Truman did decide not to use a third bomb. Could he have decided not to use the second bomb, or even the first bomb? Might Roosevelt, who was privy to all the bomb’s secrets, have stopped the juggernaut before destroying Hiroshima? Probably not.


The archives show that senior officials did mull the notion of a peaceful demonstration, proposed by Franck, Szilard, and others. However, the officials rejected the idea.

First, they reasoned, the bomb could be a dud—in which case a demonstration would be counterproductive; it might convince the Japanese that they could fight on without fear of some superweapon. Even if the next bomb—the bomb that hit Japan—did explode with great magnitude, they might see its success as the fluke.

Second, most senior officials by this time had dropped whatever resistance they might have once had to the notion of killing mass numbers of civilians for “psychological” impact. Giving the Japanese any sort of warning, much less a demonstration, would blunt the surprise—and thus its impact.

The archives reveal Japanese cable traffic—which Americans had decoded—suggesting a possible readiness to surrender even before the bombs dropped. U.S. officials pursued these hints, but, as other documents show, they led nowhere. Certainly some Japanese officials, and many people, were weary of war, but the top military officers, who effectively ran the government, were keen to fight on—and thought they could defeat the Allies once they hit the Japanese mainland. In fact, they surrendered, even after the atomic bombings, only when Emperor Hirohito overruled Japan’s official powers, invoking his godlike status in a one-time-only sidestepping of normal procedures. Had he not done so, the military might have fought on.


After the war, some reports maintained that 250,000 U.S. soldiers might have died in the invasion of Japan, which was scheduled for August. In fact, at the time, the estimate was 31,000 in the first 30 days. Still, that’s a lot of dead soldiers. After four years of deadly combat, especially amid the brutal war in the Pacific, no president would have decided not to drop an extremely powerful bomb—a bomb that, moreover, had been built at great expense—if there was a possibility that it could end the war and thus preempt the need for an invasion.

At least one senior U.S. official saw a side benefit to the bomb. In May 1945, Secretary of War Henry Stimson told his assistant secretary, John McCloy, that possession of the bomb might give the U.S. enormous leverage—“a royal straight flush”—over the Soviet Union in the coming postwar competition, which many were seeing as inevitable. Truman was traveling to the Potsdam Conference to discuss the end of the war and the division of postwar Europe with Josef Stalin and Winston Churchill, when the Trinity test occurred. He told Stalin that his scientists had tested a superweapon. Stalin didn’t seem impressed, replying only that he hoped it would force Japan to surrender. Stalin of course already knew about the Manhattan Project, thanks to a few Soviet spies on the scene. Two days after Hiroshima, Soviet troops invaded Japan through Manchuria, as Stalin had agreed to do, though the dropping of the bomb pushed up his schedule by several days, so he could grab some of the victory—and territory. Some Japanese officials had been reaching out to Moscow to help them end the war on good terms. The sequence of Hiroshima, then Stalin’s invasion, then Nagasaki quashed such hopes.


In any case, the bomb gave the U.S. no discernible advantage in the early years of the Cold War, when the Soviets occupied all of Eastern Europe and tried to make moves on Italy, Greece, and Turkey. In 1949, the Soviets built and tested their own A-bomb. The result was an arms race, which, within a decade, settled into a stalemate of overkill, in which neither side would “win” a nuclear war, regardless of who fired first.

In the three weeks between Trinity and Hiroshima, few Americans in a position of power were pondering the long-term implications of the bomb, nor did they have much basis for doing so. Outside the small group of physicists working on the project, no one quite grasped just how powerful this new weapon was; the horror of radioactive fallout was still less fully absorbed. The bomb’s consequences for future matters of war and peace—“political and social problems,” as Franck and Szilard put it—took a back seat to the understandably urgent task of winning the current war before tens of thousands more American troops were sent to their doom.

Revolutions in warfare often come at times when short-term priorities override futuristic philosophizing. After the 2010 cyberattack known as Stuxnet—in which the U.S. and Israel jointly sabotaged the centrifuges in Iran’s Natanz reactor, setting back the country’s nuclear program by a few years—retired Gen. Michael Hayden, former director of the CIA and NSA, likened the attack to Hiroshima. “I don’t want to pretend it’s the same effect,” he told the New York Times’ David Sanger, recognizing that the A-bomb was of course much more destructive, “but in one sense at least, it’s August 1945.”


He went on: “Previous cyber attacks had effects limited to other computers.” Stuxnet, however, was “the first attack of a major nature” that caused “physical destruction.” Hayden supported the attack, saying, “I think destroying a cascade of Iranian centrifuges is an unalloyed good.” Even so, he cautioned, “Somebody has crossed the Rubicon. We’ve got a legion on the other side of the river now.”

Something had shifted in the nature and calculus of warfare. Not long after, in retaliation, Iran launched a cyberattack on Aramco, the U.S.-Saudi oil company, wiping out all its hard drives. North Korea launched a cyberattack on Sony Pictures, avenging the studio’s release of a movie poking fun at—and depicting the assassination of—its leader, Kim Jong-un. More than 20 countries now have cyberunits within their military. We don’t yet know whether this will transform the nature of warfare or merely expand its terrain.

The officials and officers who put the Manhattan Project in motion, and did nothing to stop it, didn’t know what its ultimate impact would be either—until after it was used and its awful effects were recorded. Even then, for many years after, the officers in charge of war plans portrayed the atomic bomb—and then the hydrogen bomb—as ordinary weapons, writ large. Until the 1970s, nuclear weapons remained the centerpiece of those war plans.

This is no longer true, but, even so, the officers at U.S. Strategic Command and various civilian strategists in the Pentagon and various think tanks are seeking new ways to design nuclear weapons “smaller” (which is to say, only a little bit less powerful than the Hiroshima bomb) and more “versatile,” to make them more “usable” in a conflict that gets out of hand. A new era came into being in August 1945, and we are still very much living in it, with no visible way out.

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Update, Aug. 7, 2020: This post has been updated to add that the estimate of 31,000 deaths at the time was for the first 30 days of additional combat.

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