Seventy-five years ago in summer 1945, the United States’ plans for unleashing its atomic bombs went beyond Hiroshima and Nagasaki.


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Focusing his gaze on Japan, Maj. Gen. Leslie R. Groves, head of the Manhattan Project that built the first atomic bombs, studies a map of the Pacific theater in summer 1945.


Seventy-five years ago in summer 1945, the United States’ plans for unleashing its atomic bombs went beyond Hiroshima and Nagasaki.

Warfare changed forever in the summer of 1945, when the United States detonated the world’s first atomic bombs. One was tested in the New Mexico desert, and the other two devastated the Japanese cities of Hiroshima and Nagasaki. Entire cities and their populations could now be wiped out with one strike. But until Japan’s final surrender offer, five days after the Nagasaki bombing, the atomic bomb’s reputation as a “war ender” would not take hold. During that time, the question of how the next atomic bomb would be used was a real one.

One of the most persistent claims about the end of World War II is that the United States had no more atomic bombs after the second attack and that President Harry Truman was bluffing when he promised to drop more on Japan if it did not unconditionally surrender. But this is a myth: It was no bluff.

In the closing months of World War II, the United States was producing as many atomic bombs as it could. Days away from having another bomb for a third attack, the United States was close to preparing it for deployment before the Japanese surrendered. Just hours before hearing of Japan’s final surrender on August 14, 1945, Truman had ruefully told a British diplomat that he had “no alternative” but to order a third atomic bomb attack. Had World War II lasted a few more days, the odds of a third bomb—and several more—were very high.

Building the bombs

The first atomic weapons were built by the Manhattan Project, a top secret effort authorized by President Franklin Roosevelt in late 1942. Hundreds of sites and facilities spanned the country (and a few were in other countries), all collaborating to build this new weapon.

The most difficult part of the process, making the fuel for the bombs—enriched uranium and plutonium—consumed almost all of the expense and labor. In July 1945 the United States had produced enough fuel for three complete bombs—“Gadget” (plutonium), “Little Boy” (uranium), and “Fat Man” (plutonium)— with almost enough plutonium left over for a fourth. The Manhattan Project’s factories could produce enough fuel for a little under three and a half bombs per month, but tweaks to the designs of the bombs were being considered that would allow them, if the war continued, to produce several more bombs per month.

On July 16, 1945, Gadget was detonated in the New Mexico desert in a test called Trinity. It was an unambiguous success: The explosion was several times more powerful than scientists had predicted. Just after Trinity, Maj. Gen. Leslie R. Groves, the military head of the Manhattan Project, predicted to J. Robert Oppenheimer, the scientific director of the project, that it would probably require dropping not just two bombs but a third, “in accordance with our original plans.” He even thought that perhaps as many as four bombings could be necessary. (Here’s what happened that day in the New Mexico desert.)

General Groves’s view was not unusual. The U.S. plans never projected that two atomic bombs would end the war; officials felt they would need to use atomic warfare and invade. They believed that the atomic bomb would be a potent new weapon, but it was unclear whether it would be viewed as a decisive one. How the atomic bombs would affect the Japanese cabinet’s will to fight was a complete unknown.

The Americans knew from intercepted Japanese foreign intelligence communications that the Japanese high cabinet was divided. The Japanese militarists, who held a cabinet majority in mid-1945, believed that they should “bleed” the Americans, in the vain hope that the U.S. public would tire of war. A “peace” faction saw this tactic for the folly it was, and that it would mean the destruction of Japan.

If the United States wanted Japan to surrender, it had to find a way to overcome the militarist domination. Conventional bombing alone would not do the trick. U.S. firebombing had routinized destruction of Japanese cities since March 1945. The first massive nighttime raids against Tokyo killed more than 100,000 and left a million people homeless over the course of one night. By July the United States had bombed more than 60 other Japanese cities in this way, with no appreciable change in the Japanese stance on surrender. If the atomic bomb would have an immediate effect, it had to be understood as a revolutionary weapon.

Choosing a target

The American planners wanted the first use of the atomic bomb to make its implications clear, and so they gave careful consideration to how it would first be used. The Manhattan Project’s Target Committee, led by U.S. scientists and key members of the military, met in spring 1945 to discuss the cities that might become the first targets. At the first meeting in late April 1945 (about a week before Germany’s surrender), they defined candidates as “large urban areas of not less than 3 miles in diameter existing in the larger populated areas . . . between the Japanese cities of Tokyo and Nagasaki . . . [and] should have high strategic value.” Specifically they considered 17 possibilities: Tokyo Bay, Kawasaki, Yokohama, Nagoya, Osaka, Kobe, Kyoto, Hiroshima, Kure, Yamata, Kokura, Shimosenka, Yamaguchi, Kumamoto, Fukuoka, Nagasaki, and Sasebo.

In early May 1945 after another Target Committee meeting, the list had been amended and revised. It now included just five cities: Kyoto, Hiroshima, Yokohama, Kokura, and Niigata (in order of interest). Kyoto was the top pick as it was a large city and as yet untouched by bombing. Hiroshima, another untouched city, was added for the large military base in its center and its geography: The surrounding hills would “focus” the blast and increase its destructive power.

By the end of June, the Committee put Kyoto, Hiroshima, Kokura, and Niigata on a list of “reserved targets” to “protect” them from any future fire bombing raids (fire bombed at the end of May, Yokohama was no longer eligible). Kyoto was removed as a candidate for any attack—atomic or otherwise—shortly afterward because Secretary of War Henry Stimson, for reasons both strategic and sentimental, decided to save the former Japanese capital. Groves protested vigorously, repeatedly arguing that Kyoto was a valid and important target, but Stimson ultimately convinced Truman to agree with him. Kyoto was off the list. (See maps of nine key moments that defined WWII.)

At the Potsdam Conference in July 1945, Truman and Stimson learned of the Trinity test, which electrified the president. Previously he had been fairly disinterested in the scientific tinkering taking place in New Mexico, but he now saw this new weapon as a means of waging war against Japan and sending a message to the Soviet Union.

The target list was being finalized in encrypted communications between Stimson, at Potsdam, and Groves, in Washington, D.C. Groves decided each primary target had to have viable backups in case of foul weather or other complications. Maj. Gen. Lauris Norstad, head of target planning for the Army Air Forces, supplied them. With Kyoto removed, they needed another backup in the area of Hiroshima and Kokura. Though it had unfavorable topography and a POW camp, Nagasaki, a port city on the Japanese island of Kyushu that was home to two munitions factories, was added to the list.

The final target order was drafted by Groves, shown to Truman, approved by Stimson and Gen. George Marshall, chief of staff of the U.S. Army, and issued on July 25. A directive was sent from Lt. Gen. Thomas Handy, deputy chief of staff, to Gen. Carl Spaatz, commander of the Strategic Air Forces in the Pacific. It said that “after about 3 August 1945,” the 20th Air Force would deliver its first “special bomb” on Hiroshima, Kokura, Niigata, or Nagasaki (an earlier draft made it clear this was the order of priority). The bombing would be done visually (not by radar), and the bomber would be accompanied only by a few observation aircraft. Furthermore, “additional bombs will be delivered on the above targets as soon as made ready by the project staff. ”New targets would be chosen once the first four were eliminated. It was not an order to drop one atomic bomb; it was an order to permit the dropping of as many atomic bombs that were or would become available.

The first attack

The launching point for the heavy bombing attacks against Japan, including both the atomic and firebombing raids, was the small island of Tinian in the Northern Marianas. Captured from the Japanese in summer 1944, Tinian was turned into an island-size air base, the largest in the entire war. (The Battle of Iwo Jima still haunts this veteran 75 years later.)

Starting in May 1945, around the same time that target planning had begun, infrastructure to assemble atomic bombs was set up on Tinian. Plans were drawn up to get the valuable bomb components to the island without mishap. On July 16, the day of the Trinity test, components of Little Boy began their journey to Tinian. All arrived by July 29, and the bomb was ready to drop at the end of the month. The Fat Man materials all arrived by August 2, and assembly of the second bomb was finished on August 7. Orders specified that the targets needed to be sighted visually, out of fear that errors could be introduced by radar targeting. (It intuitively does not seem like one could “miss” with an atomic bomb, but for weapons the size of those used in World War II, being off by several miles—very easy with radar guidance—could mean the difference between hitting or grazing a target.)

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The B-29
Enola Gay conveyed the “Little Boy” uranium bomb that was dropped on Hiroshima, Japan, on August 6, 1945.

Visual sighting meant that the skies had to be relatively clear, so every day lone B-29s would fly to targets and radio back weather reports. On August 5, skies were finally deemed clear enough for a bombing run the next day. That night, Little Boy was loaded into a B-29 bomber, the Enola Gay, and sent to bomb a city, either Hiroshima, Kokura, or Nagasaki.

Around 1 a.m. on August 6, the plane took off. Cloud cover was light over Hiroshima, and shortly after 8: 00 a.m., the city came into sight. At 8: 15, Little Boy dropped, fell for 44 seconds, and then detonated with the force of roughly 15,000 tons of TNT. Almost instantly, Hiroshima erupted in a maelstrom of fire and destruction; tens of thousands would die within minutes, and perhaps 100,000 more would succumb in the aftermath. The Enola Gay observed this from 32,700 feet, circled for less than an hour, and headed back to Tinian. (For those who survived, memories of the bomb are impossible to forget.)

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Frozen at 8: 15, the hands of a watch recovered from Hiroshima stopped when the atomic bomb fell on the city.

The second attack

When Truman heard about the run on Hiroshima, he was traveling home from Potsdam on the battleship U.S.S. Augusta. He was overjoyed at its success, announcing that it was “the greatest thing in history.” The news of the atomic bomb was almost immediately released to the press, and a radio announcement was broadcast to Japan itself.

The Japanese military knew that Hiroshima had come under some kind of major attack on August 6, but did not know its special nature. After hearing about the American radio announcement, the high command met and agreed that they should send a scientific team to investigate. A top Japanese nuclear physicist, Professor Yoshio Nishina, reported back from Hiroshima on August 8 that there were “almost no buildings left standing,” and that, from what he could tell, “the so-called new type bomb is actually an atomic bomb.”

As the Japanese were confirming what happened in Hiroshima, the next bombing mission was already beginning. On August 8, weather forecasters were predicting that August 10, the planned date for the second attack, was going to be unfavorable. Instead, U.S. officials on Tinian, without consulting anyone in Washington, D.C. (including Truman or even Stimson), decided that they had the authority under the launch order to use the next weapon. So in a marathon session, they assembled Fat Man, loaded it into another B-29, the Bockscar, and sent it on its way.

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The massive plutonium “Fat Man” bomb is lowered to a carriage on Tinian Island before being loaded onto the B-29,
Bockscar. The United States dropped Fat Man on the Japanese city of Nagasaki on August 9, 1945.

Kokura, an arsenal town on the northern end of the southern Japanese island of Kyushu, was the primary target. Visibility there was terrible, as Kokura was covered in clouds or smoke (it may have been both: The nearby city of Yawata had been firebombed the day before). After spending 45 minutes fruitlessly searching for Kokura, the Bockscar proceeded to Nagasaki. At 11: 02 a.m. on August 9, 1945, Fat Man exploded over Nagasaki with the violence of 20,000 tons of TNT. More than 70,000 people were killed in the immediate attack. Bockscar briefly surveyed the damage and then headed back to base. (Here’s how five people survived the blast in Nagasaki.)

The Japanese high command was meeting on August 9 to discuss the Soviet Union’s recent declaration of war on Japan and its subsequent invasion of Manchuria when they learned of the attack on Nagasaki. It is hard to know if the Japanese believed more atomic attacks would be coming. Certainly the use of a second bomb dashed any hopes that the United States only had one. But neither the second atomic bomb nor the Soviet invasion was enough to push the Japanese to unconditional surrender: Japanese officials were prepared to offer only a conditional surrender to the Americans, preserving the role and power of the emperor.

Waiting and preparing

In the U.S. capital things were chaotic. On August 10, Japan’s offer of conditional surrender was scrutinized closely by Truman and his Cabinet, while General Groves sent a letter to General Marshall, the chief of staff, reporting that “the next bomb” would be ready earlier than expected. In Los Alamos, New Mexico, scientists were working around the clock finalizing the components for the next bomb to ship to Tinian. They would be shipping the final components from New Mexico on August 12 or 13, and would be ready to drop it on a Japanese city in about a week. (Pictures of Hiroshima and Nagasaki show the destructive power of atomic bombs.)

Truman was informed of this, and his response was immediate. As Marshall wrote back to Groves: “It is not to be released over Japan without express authority from the President.” Truman may have had a very peripheral role in the ordering of the use of the atomic bomb—his main role, as Groves later put it, was not to interfere with plans already in motion—but he played a direct role in the stopping of the use of further bombs.

Why did Truman, who had proclaimed the Hiroshima attack to be “the greatest thing in history,” suddenly order the stoppage? Some believe he was worried that another atomic bomb would disrupt efforts to end the war, not speed them along. Other historians believe Truman wanted to stop the carnage. He told his Cabinet that morning, as recounted in the diary of Henry Wallace, his secretary of commerce and the former vice president, that he ordered the stoppage because “the thought of wiping out another 100,000 people was too horrible. He didn’t like the idea of killing, as he said, ‘all those kids.’”

Either way, Truman was seeking to regain control, having permitted, perhaps without realizing it, the military to consider itself totally in control of how these new weapons would be used. He had known the first atomic attack was happening, but not the second. If a third was to happen, it would come from his direct order.

A third shot?

Japan’s initial surrender offer was a promising sign, but not enough for Truman and his Cabinet. Only unconditional surrender would do, Truman replied. Several days of waiting—from August 10 to August 14—followed. Speculation in the American press and military was rampant about if and where more atomic bombs would fall.

After being told not to use the bomb, Groves called Oppenheimer in New Mexico the next day and told him not to ship the next plutonium core to Tinian. In the same discussion, though, Oppenheimer told Groves that he could report on their progress on a new weapon design, a “composite” implosion bomb that would use both plutonium and enriched uranium in one bomb, allowing them to improve their production rate dramatically.

Even though Truman had put a hold on atomic bombing, the leaders of the U.S. Army Air Forces still thought that more bombs would be needed. On August 10, General Spaatz telegrammed General Norstad, in target planning, to “strongly recommend” that the next atomic bomb target be Tokyo. “More destruction would be obtained from using a clean target,” he wrote, “but it is believed that the psychological effect on the government officials [there] is more important at this time than destruction.” (See the effects of nuclear bomb testing on people in eastern Kazakhstan.)

The same day he learned that his suggestion was “being considered on a high level.” It promised that “final decisions” would be made in the next two days. The same day, Maj. Gen. Curtis LeMay, architect of the firebombing campaigns, put forward an urgent request to install facilities capable of assembling atomic bombs at Okinawa, perhaps anticipating the use of the weapon for the invasion of Japan.

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Hiroshima was still in ruins in March 1946. Exact death counts are impossible to obtain, but experts estimate as many as 100,000 died from the immediate explosion and the aftereffects of the bomb.

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On August 13, Secretary of War Stimson indicated that perhaps the “shipments” of nuclear materials to Tinian should resume. Groves was tasked with getting the most up-to-date information on the schedule of future bombings and making sure it was passed along to General Marshall. Marshall was wondering whether it made sense to use the bombs as they were ready, or whether they should be collected and used for the invasion. The number of possibly dropped atomic bombs in such a situation was about a dozen. In any case, a third bomb, a representative of Groves’s told a representative of Marshall’s, was “ready to be shipped—waiting on order now.”

On August 14, Spaatz continued to push Tokyo as the next target, recommending with “utmost urgency” that they transfer the third atomic bomb to Tinian “to be dropped on Tokyo.” Again, he was told that the decision was still pending. Groves was told that the decision about whether to use another atomic bomb would be made the next day.

Later that afternoon, Truman met with the British ambassador and “remarked sadly” that since the Japanese seemed unwilling to surrender unconditionally, “he now had no alternative but to order an atomic bomb to be dropped on Tokyo.” If he made the order, the operation would have taken place within days.

The war’s end

But fortunately, it did not come to that. Not long after Truman talked with the British ambassador, on August 14, 1945, Japan announced its embrace of unconditional surrender. Historians still argue today about what exactly caused their change of heart, as the relative roles of the atomic bombs, the Soviet declaration of war, and internal Japanese forces are very difficult to disentangle, and all likely played a part.

The third bomb, and the others that may have followed, were a definitive part of the American strategy to end World War II. Although hopeful that nuclear weapons might end the war, American officials—from President Truman to his commanding officers—did not expect the war to end right away. Signs indicated that more atomic weapons were necessary, and U.S. leaders were rapidly moving to order more atomic strikes. Had the war continued, more atomic bombs would very likely have been used.

If they had been, would atomic bombs still be considered “war enders”? If not, would they have been more likely to have been used in the Cold War? Of course, there’s no way to know for sure. But the third bomb was closer to being used than most realize.

Alex Wellerstein is a historian of science and nuclear weapons. A professor at the Stevens Institute of Technology, he is the author of
Restricted Data: The Nuclear Secrecy Blog.