Why Was the Decision Made to Use the Atomic Bomb on Japan?

60th Anniversary Of The Atomic Bomb Of Nagasaki
View of the radioactive plume from the bomb dropped on Nagasaki City, as seen from 9.6 km away, in Koyagi-jima, Japan, August 9, 1945. The US B-29 superfortress Bockscar dropped the atomic bomb nicknamed 'Fat Man,' which detonated above the ground, on northern part of Nagasaki City just after 11am. Handout / Getty Images

The decision to use the atomic bomb to attack two Japanese cities and effectively end World War II remains one of the most controversial decisions in history. The conventional view, going back to the initial press coverage in 1945, was that the use of atomic weapons was justified as it ended a long and very costly war. However, over the intervening decades, other interpretations of the decision to strike two Japanese cities have been offered.

Alternative explanations include the idea that the United States was largely interested in using atomic weapons as a way of ending the war quickly and keeping the Soviet Union from getting involved in the fighting in the Pacific.

Fast Facts: Decision to Drop the Atomic Bomb

  • President Truman made the decision to use the atomic bomb with no public or congressional debate. He later formed a group known as the Interim Committee to decide how—but not whether—the bomb should be used.
  • A small group of renowned scientists, including some involved in the creation of the bomb, advocated against its use, but their arguments were essentially ignored.
  • The Soviet Union was set to enter the war in Japan within months, but the Americans were wary of Soviet intentions. Ending the war quickly would prevent Russian participation in the fighting and expansion into parts of Asia.
  • In the Potsdam Declaration, issued on July 26, 1945, the United States made a call for the unconditional surrender of Japan. Japan's rejection of the demand led to final order to proceed with atomic bombing.

Truman's Options

When Harry Truman became president after the death of Franklin D. Roosevelt in April 1945, he was informed of a momentous and extraordinarily secret project: the development of the first atomic bomb. A group of scientists had approached Roosevelt years earlier, expressing fear that Nazi scientists would develop an atomic bomb. Eventually, the Manhattan Project was organized to create an American super weapon fueled by an atomic reaction.

By the time Truman was informed of the Manhattan Project, Germany was nearly defeated. The remaining enemy of the United States, Japan, continued fighting in an incredibly bloody war in the Pacific. In early 1945, campaigns on Iwo Jima and Okinawa proved very costly. Japan was being heavily bombed by formations of a new bomber, the B-29. Despite heavy casualties, especially among Japanese civilians killed in an American incendiary bombing campaign, the Japanese government seemed intent on continuing the war.

Manhattan Project officials including Dr Robert J Oppenhe
JULY 16, 1945: Manhattan Project officials, including Dr. Robert J. Oppenheimer (white hat) and General Leslie Groves (next to him), inspect detonation site of the Trinity atomic bomb test. The LIFE Picture Collection/Getty Images / Getty Images

In the spring of 1945, Truman and his military advisers had two obvious options. They could resolve to fight a prolonged war against Japan, which would probably mean having to invade the Japanese home islands in late 1945 and perhaps even continue fighting into 1946 or beyond. Or they could continue working on acquiring a functional atomic bomb and seek to end the war with devastating attacks on Japan.

Lack of Debate

Before the atomic bomb was used for the first time there was no debate in Congress or among the American public. There was a simple reason for that: almost no one in Congress had been aware of the Manhattan Project, and the public had no inkling that a weapon that could end the war was on the horizon. Even the many thousands who worked on the project at various labs and secret facilities were unaware of the ultimate purpose of their labor.

Yet in the summer of 1945, as the atomic bomb was being prepared for its final testing, a closely contained debate over its use did emerge within the circle of scientists who had contributed to its development. Leo Szilard, a refugee Hungarian physicist who had petitioned President Roosevelt to begin work on the bomb years earlier, had grave concerns.

The main reason Szilard had urged the United States to begin work on the atomic bomb was his fear that Nazi scientists would develop nuclear weapons first. Szilard and other European scientists who worked on the project for the Americans had considered the use of the bomb against the Nazis to be legitimate. But with Germany’s surrender in May 1945, they had concerns about using the bomb against Japan, which did not seem to be developing its own atomic weapons.

Szilard and physicist James Franck submitted a report to Secretary of War Henry L. Stimson in June 1945. They argued that the bomb should be not be used against Japan without warning, and that a demonstration explosion should be arranged so the Japanese leadership could understand the threat. Their arguments were essentially ignored.

The Interim Committee

The secretary of war formed a group called the Interim Committee, which was tasked with deciding how the bomb was to be used. The issue of whether it should be used was not really an issue. The thinking in the highest levels of the Truman administration and the military was quite clear: if the atomic bomb could shorten the war, it should be used.

Experts Meeting to Discuss Future of Atomic Energy
(Original Caption) President Harry S. Truman met to discuss the future uses of atomic energy with a group of scientists and cabinet members at the White House. Together after meeting with the president are (left to right): George L. Harrison, special consultant to the secretary of war; Major General Leslie Richard Groves, in charge of the government's atomic bomb project; Dr. James Conant, chairman of the National Defense Research Committee and president of Harvard University; and Dr. Vannevar Bush, director of the Office of Scientific Research and Development and president of the Carnegie Institute of Washington, DC. Above group makes up the Interim Committee to investigate the future uses of atomic energy. Bettmann Archive / Getty Images

The Interim Committee, which comprised government officials, military officers, scientists, and even a public relations expert, determined that targets for atomic bombs should be a military-industrial facility deemed important to Japan’s war-related industries. Defense factories tended to be located in or near cities, and would naturally be located not far from housing for many civilian workers.

So it was always assumed that civilians would be in the target zone, but that was not unusual in the context of the war. Many thousands of civilians had died in the Allied bombing of Germany, and the firebombing campaign against Japan in early 1945 had already killed as many as a half-million Japanese civilians.

Timing and the Soviet Union

As the world’s first atomic bomb was being readied for a test blast in a remote desert area of New Mexico in July 1945, President Truman traveled to Potsdam, a suburb of Berlin, to meet with Britain’s Prime Minister Winston Churchill and the Soviet dictator Joseph Stalin. Churchill had known the Americans had been working on the bomb. Stalin had been officially kept in the dark, though Soviet spies working within the Manhattan Project had been passing along information that a major weapon was being developed.

One of Truman’s considerations at the Potsdam Conference was the entry of the Soviet Union into the war against Japan. The Soviets and the Japanese were not at war, and were actually adhering to a non-aggression pact signed years earlier. In meetings with Churchill and President Roosevelt at the Yalta Conference in early 1945, Stalin had agreed that the Soviet Union would attack Japan three months after the surrender of Germany. As Germany had surrendered on May 8, 1945, that placed the Soviet Union's entry into the Pacific war on August 8, 1945.

A Meeting During the Potsdam Conference
British, Soviet and American military leaders meet during the Potsdam conference to discuss the future of post-war Germany. Corbis via Getty Images / Getty Images

As Truman and his advisers saw it, Russian help fighting Japan would be welcomed if the Americans would be facing more years of grueling combat. However, the Americans were very wary of Soviet intentions. Seeing the Russians acquire influence over Eastern Europe, there was a great interest in preventing Soviet expansion into parts of Asia.

Truman knew that if the bomb worked and could possibly end the war quickly, he could prevent widespread Russian expansion in Asia. So when a coded message reached him in Potsdam informing him that the bomb test was successful, he could engage Stalin with greater confidence. He knew he would not need Russian help to defeat Japan.

In his handwritten journal, Truman jotted down his thoughts in Potsdam on July 18, 1945. After describing a conversation with Stalin, he noted, “Believe Japs will fold up before Russia comes in. I am sure they will when Manhattan [referring to the Manhattan Project] appears over their homeland.”

Surrender Demand

At the Potsdam conference, the United States issued a call for unconditional surrender of Japan. In the Potsdam Declaration, issued on July 26, 1945, the United States, Great Britain, and the Republic of China argued that Japan’s position was futile and its armed forces should surrender unconditionally. The document’s final sentence stated: “The alternative for Japan is prompt and utter destruction.” No specific mention was made of the atomic bomb.

On July 29, 1945, Japan rejected the Potsdam Declaration.

American Warning Letter to People of Japan
This letter of warning to the Japanese people was dropped from airplanes over Japanese cities following the first Hiroshima atomic bomb blast. Corbis via Getty Images / Getty Images

Two Bombs

The United States had two atomic bombs ready to use. A target list of four cities had been determined, and it was decided that the bombs would be used after August 3, 1945, as weather permitted. 

The first atomic bomb was dropped on the city of Hiroshima on August 6, 1945. Its destruction was enormous, but Japan still did not appear willing to surrender. On the morning of August 6 in America, radio stations played a recorded address by President Truman. He announced the use of the atomic bomb and issued a warning to the Japanese that more atomic bombs could be used against their homeland. 

The Japanese government continued to reject calls for surrender. The city of Nagasaki was attacked with another atomic bomb on August 9, 1945. Whether or not the dropping of the second atomic bomb was necessary has long been debated.

Controversy Endures

Over the decades, it was generally taught that the use of the atomic bomb was to end the war. However, over time the issue of its use being part of an American strategy to contain the Soviet Union has also gained credence.

A national controversy over the decision to use the atomic bomb erupted in the mid-1990s, when the Smithsonian Institution made changes to a proposed exhibit featuring the Enola Gay, the B-29 that dropped the Hiroshima bomb. As originally planned, the exhibit would have included criticism of the decision to drop the bomb. Veterans groups, arguing that the use of the bomb saved the lives of troops who would have died in combat during an invasion of combat, protested the planned exhibit.


  • Cheek, Dennis W. "Atomic Bomb." Encyclopedia of Science, Technology, and Ethics, edited by Carl Mitcham, vol. 1, Macmillan Reference USA, 2005, pp. 134-137. Gale Virtual Reference Library.
  • Fussell, Paul. "The Atomic Bombings Ended the Savagery of Both Sides." The Atomic Bombings of Hiroshima and Nagasaki, edited by Sylvia Engdahl, Greenhaven Press, 2011, pp. 66-80. Perspectives on Modern World History. Gale Virtual Reference Library.
  • Bernstein, Barton J. "Atomic Bomb." Ethics, Science, Technology, and Engineering: A Global Resource, edited by J. Britt Holbrook, 2nd ed., vol. 1, Macmillan Reference USA, 2015, pp. 146-152. Gale Virtual Reference Library.
mla apa chicago
Your Citation
McNamara, Robert. "Why Was the Decision Made to Use the Atomic Bomb on Japan?" ThoughtCo, Aug. 2, 2021, thoughtco.com/why-was-the-decision-made-to-use-the-atomic-bomb-on-japan-4628277. McNamara, Robert. (2021, August 2). Why Was the Decision Made to Use the Atomic Bomb on Japan? Retrieved from https://www.thoughtco.com/why-was-the-decision-made-to-use-the-atomic-bomb-on-japan-4628277 McNamara, Robert. "Why Was the Decision Made to Use the Atomic Bomb on Japan?" ThoughtCo. https://www.thoughtco.com/why-was-the-decision-made-to-use-the-atomic-bomb-on-japan-4628277 (accessed March 28, 2023).