Hiroshima Atomic Bombing: What Happened on August 6, 1945?

At 8:15 a.m. on August 6, 1945, a U.S. atomic bomb exploded over Hiroshima, Japan. The blast and the fires it ignited devastated the city. Tens of thousands died immediately; injuries and radiation exposure killed many more in the months that followed. Hiroshima became the first city attacked with a nuclear weapon in war.

Aerial view of Hiroshima after the atomic bombing, August 1945. U.S. Navy, public domain. Image record.

Why Hiroshima was bombed

By the summer of 1945, Nazi Germany had surrendered, but the war between Japan and the Allies continued. U.S. forces had captured Okinawa after costly fighting, and American leaders demanded Japan’s surrender in the Potsdam Declaration of July 26. The Japanese government did not accept its terms before the bombing.

President Harry S. Truman and his advisers sought to force a rapid end to the war. Hiroshima had military facilities and was an important regional headquarters, but it was also a city of homes, schools and hospitals. Choosing an urban target meant civilians would be exposed to the weapon’s effects. The decision to use atomic bombs, and the alternatives available, remain subjects of historical debate.

What happened on August 6, 1945?

The U.S. B-29 bomber Enola Gay dropped a uranium bomb nicknamed Little Boy. It detonated roughly 600 meters (about 2,000 feet) above Hiroshima. The explosion produced intense heat, a powerful blast wave and radiation. Fires spread through the damaged city as people searched for relatives and medical help.

Hiroshima’s account of the destruction says almost all buildings within two kilometers of the point beneath the explosion were destroyed or burned. The city’s population at the time was approximately 350,000, including residents, military personnel, workers brought in from nearby towns, people from Japan’s colonies and some prisoners of war.

The exact death toll cannot be established. The City of Hiroshima estimates that approximately 140,000 people had died by the end of 1945. That figure includes people who survived the initial blast but later died from burns, injuries and acute radiation effects; it is not a count of those killed instantly.

Hiroshima in October 1945, two months after the bombing. Photo: Yoshito Matsushige, public domain. Image record.

The survivors and the effects of radiation

Survivors, known in Japanese as hibakusha, faced injuries that could change over time. Burns and wounds were followed for some by fever, nausea, diarrhea and other signs of acute radiation sickness. In later years, increased cases of leukemia and other cancers emerged among exposed populations. The bombing also destroyed families, workplaces, medical services and records, making rescue and recovery more difficult.

The people harmed were not all Japanese citizens. Hiroshima included Koreans and Taiwanese from territories then under Japanese colonial rule, people from mainland China, foreign students and U.S. prisoners of war. Their presence is part of the city’s historical record.

How the bomb was made — and what followed

Little Boy used enriched uranium produced at Oak Ridge, Tennessee, for the secret U.S. program known as the Manhattan Project. That program also produced a different, plutonium-based weapon. The science, industrial sites and people behind the bombs are covered in our separate explainer.

Three days after Hiroshima, the United States dropped a second atomic bomb on Nagasaki.

The Soviet Union declared war on Japan on August 8 and invaded Japanese-occupied Manchuria. Japan agreed to surrender on August 14; Emperor Hirohito announced the decision on August 15, and the formal surrender was signed on September 2. The bombings and Soviet entry into the war were both major developments in those final days. Historians continue to debate their relative weight in Japan’s decision.

The building later known as the Atomic Bomb Dome, amid ruins in October 1945. Photo: Shigeo Hayashi, public domain. Image record.

Hiroshima’s legacy

The city was rebuilt, while survivors carried the physical and emotional effects of the bombing for decades. A 1949 Japanese law supported Hiroshima’s reconstruction as a peace memorial city. The preserved Atomic Bomb Dome later became a UNESCO World Heritage Site.

Hiroshima is now both a living city and a place of remembrance. Its history preserves the human consequences of nuclear warfare alongside the record of the decisions and technology that made the attack possible.

Sources

• City of Hiroshima — The Realities of the Atomic Bombing: damage, population, death estimate and long-term effects.
• City of Hiroshima — Death toll FAQ: why the precise death toll is unknown.
• City of Hiroshima — Why was Hiroshima targeted?: military facilities and target selection.
• U.S. National Archives — The Atomic Bombing of Hiroshima and Nagasaki: mission, chronology and debate.
• National Park Service — Manhattan Project: uranium bomb, Soviet entry and surrender.
• U.S. Holocaust Memorial Museum — World War II in the Pacific: late-war context and surrender chronology.
• City of Hiroshima — Peace Memorial City Construction Law: reconstruction.
• UNESCO — Hiroshima Peace Memorial: preservation of the Atomic Bomb Dome.