The atomic bombings of Hiroshima and Nagasaki were two nuclear attacks carried out by the United States against Japan on 6 August and 9 August 1945, respectively, during the final weeks of World War II in the Pacific. The United States Army Air Forces dropped a uranium gun-type bomb (“Little Boy”) on Hiroshima and a plutonium implosion-type bomb (“Fat Man”) on Nagasaki. The bombings killed an estimated 129,000 to 226,000 people, the majority of them civilians, making them the only combat uses of nuclear weapons in history. Japan announced its surrender on 15 August 1945, with formal surrender documents signed on 2 September 1945. The bombings ended the Pacific War and ushered in the nuclear age.

By mid-1945, American forces had fought a costly island-hopping campaign across the Pacific, suffering heavy casualties at Iwo Jima and Okinawa. Allied planners were preparing for a land invasion of the Japanese home islands, projected under Operation Downfall, with casualty estimates ranging widely. Japan had suffered devastating firebombing campaigns and a naval blockade, yet its government had not offered unconditional surrender. The atomic bomb program, known as the Manhattan Project, had been under development since 1942 at a cost of roughly $2 billion, and produced its first successful test at Trinity on 16 July 1945. The Potsdam Declaration of 26 July 1945, issued by the Allied powers, demanded Japan's unconditional surrender and warned of “prompt and utter destruction” without specifying the nature of the weapon.

On 6 August 1945, the B-29 Enola Gay, piloted by Colonel Paul Tibbets, dropped Little Boy over Hiroshima, a city of military and industrial significance. The bomb detonated at approximately 580 meters altitude with a yield estimated at 15 kilotons. Estimates of immediate and near-term deaths range from 70,000 to 140,000. Three days later, on 9 August 1945, a second B-29, Bockscar, dropped Fat Man over Nagasaki after the primary target of Kokura was obscured by clouds. Fat Man yielded approximately 21 kilotons and killed an estimated 40,000 to 80,000 people in the immediate period. Both cities sustained near-total destruction within and beyond the immediate blast radius. Survivors, known in Japan as hibakusha, experienced elevated rates of radiation-related illness, including leukemia and other cancers, in the years and decades following.

Emperor Hirohito announced Japan's acceptance of the Potsdam Declaration terms on 15 August 1945, citing the destructive power of “a new and most cruel bomb.” Historians debate the relative weight of the bombings versus the Soviet Union's declaration of war against Japan on 8 August and its rapid advance into Manchuria as factors driving the surrender decision. Formal surrender was signed aboard the USS Missouri on 2 September 1945. The bombings shaped subsequent international arms control efforts, nuclear deterrence doctrine, and debates over the laws of war. The United States maintained a nuclear monopoly until the Soviet Union's first successful test in August 1949.

Historians broadly agree on the basic factual record: dates, weapons specifications, casualty ranges, and the sequence of surrender. There is no comparable consensus on the moral justification for the bombings or their causal role in Japan's surrender. See Historical Consensus and Military and Strategic Consensus.

The bombings have generated sustained moral, strategic, and historical debate across several dimensions:

• Military necessity - The dominant postwar American view holds that the bombings were necessary to end the war quickly and avoid a costly land invasion. See Military Necessity Viewpoint.
• Unnecessary or criminal - A range of critics, including some American military figures at the time, have argued Japan was near surrender and the bombings were unnecessary or constituted war crimes against civilian populations. See Unnecessary / War Crime Viewpoint.
• Soviet factor - Some historians argue the bombings were driven partly by the desire to end the Pacific War before the Soviet Union could claim territorial concessions, placing them in an emerging Cold War context as well as a military one. See Cold War Diplomacy Viewpoint.
• Japanese responsibility - A viewpoint emphasizing Japanese military conduct, the costs of the war Japan initiated, and the logic of compelling surrender as context for evaluating the bombings. See Japanese Culpability Viewpoint.
• Nuclear abolitionism - An ethical and policy viewpoint treating the bombings as a foundational argument for the elimination of nuclear weapons and the inadequacy of deterrence frameworks. See Nuclear Abolitionism Viewpoint.
• Hibakusha and humanitarian witness - A strand of the debate rooted in survivor testimony and documentary record, emphasizing the human costs of the bombings as a basis for moral and policy argument. Distinct from abolitionism in grounding its claims in lived experience rather than strategic or philosophical frameworks. See Hibakusha / Humanitarian Witness Viewpoint.

• Atomic Bombings of Hiroshima and Nagasaki - History
• Atomic Bombings of Hiroshima and Nagasaki - Debate
• Atomic Bombings of Hiroshima and Nagasaki - Historical Consensus
• Atomic Bombings of Hiroshima and Nagasaki - Military and Strategic Consensus
• Manhattan Project
• Operation Downfall
• Pacific War
• Nuclear Weapons and the Law of War
• Nuclear Deterrence
• Potsdam Declaration

1. Rhodes, Richard. The Making of the Atomic Bomb. Simon & Schuster, 1986.
2. Bernstein, Barton J. “The Atomic Bombings Reconsidered.” Foreign Affairs, vol. 74, no. 1, 1995, pp. 135-152.
3. Frank, Richard B. Downfall: The End of the Imperial Japanese Empire. Random House, 1999.
4. Hasegawa, Tsuyoshi. Racing the Enemy: Stalin, Truman, and the Surrender of Japan. Harvard University Press, 2005.
5. Walker, J. Samuel. Prompt and Utter Destruction: Truman and the Use of Atomic Bombs Against Japan. University of North Carolina Press, 1997.
6. Committee for the Compilation of Materials on Damage Caused by the Atomic Bombs in Hiroshima and Nagasaki. Hiroshima and Nagasaki: The Physical, Medical, and Social Effects of the Atomic Bombings. Basic Books, 1981.
7. Stimson, Henry L. “The Decision to Use the Atomic Bomb.” Harper's Magazine, February 1947.