On this day · 6 August

1945

On This Day in 1945: United States Drops Atomic Bomb on Hiroshima

Political event

On 6 August 1945, the United States dropped an atomic bomb on Hiroshima, killing tens of thousands and ushering the world into the nuclear age.

On 6 August 1945, the United States dropped an atomic bomb on the Japanese city of Hiroshima—the first use of a nuclear weapon in warfare.

At approximately 8.15am local time, a uranium bomb nicknamed “Little Boy” was released from the American B-29 bomber Enola Gay.

It exploded above the centre of Hiroshima with a force equivalent to approximately 15,000 tonnes of TNT.

As many as 70,000 people are estimated to have been killed immediately. By the end of 1945, deaths associated with the blast, burns and radiation exposure had increased the estimated toll to around 140,000.

The attack destroyed much of the city and marked the beginning of the nuclear age.

The Manhattan Project

The bomb was created through the Manhattan Project, the highly secret American-led programme established during the Second World War to develop an atomic weapon.

The project brought together scientists, engineers, military personnel and industrial workers across numerous sites in the United States.

Its scientific director was J Robert Oppenheimer, while General Leslie Groves oversaw the military operation.

The work was initially driven by fears that Nazi Germany might build an atomic bomb first. Germany surrendered in May 1945 without having produced such a weapon, but the war against Japan continued.

On 16 July 1945, the United States successfully detonated the world’s first nuclear device during the Trinity test in New Mexico.

Three weeks later, a different type of weapon was used against Hiroshima. Unlike the plutonium device tested at Trinity, “Little Boy” used uranium and had not previously been tested in a full nuclear explosion.

The Enola Gay takes off

During the early hours of 6 August, the Enola Gay took off from the island of Tinian in the Mariana Islands.

The aircraft was commanded by Colonel Paul Tibbets, who had named it after his mother.

Hiroshima was home to a substantial civilian population but was also an important military and communications centre. Approximately 43,000 Japanese soldiers were stationed in or around the city.

Weather aircraft flew ahead of the bombing mission to examine visibility over potential targets. Hiroshima’s relatively clear skies helped determine that it would be attacked.

At 8.15am, the bomb was released from an altitude of more than 30,000 feet.

It fell for approximately 43 seconds before detonating around 580 metres above the city.

A city destroyed in seconds

The explosion produced an intense flash of light, extreme heat and a powerful shockwave.

People close to the hypocentre were killed almost instantly. Buildings were crushed, burned or swept away, while fires spread through the city.

The US National Archives estimates that as many as 70,000 people died immediately. Many others suffered severe burns, blindness, crushing injuries and wounds caused by flying glass and debris.

Hiroshima’s ability to care for the injured was itself devastated. The International Committee of the Red Cross has reported that approximately 90% of the city’s doctors and 92% of its nurses were killed, while around 80% of its medical infrastructure was destroyed.

Survivors searched for relatives, shelter and water amid fires and ruins, often without understanding what had happened to them.

A radioactive “black rain” later fell in parts of the city, carrying soot, debris and radioactive material.

The effects of radiation

The Hiroshima bomb introduced civilians and medical workers to injuries which were not fully understood at the time.

Some people who initially appeared to have survived without serious wounds became ill during the following days and weeks. Symptoms included bleeding, fever, hair loss, weakness and infections associated with acute radiation sickness.

Other survivors experienced an increased risk of leukaemia and several forms of cancer during subsequent years.

The Japanese word hibakusha came to describe people affected by the atomic bombings of Hiroshima and Nagasaki.

Many hibakusha experienced not only physical illness but also social discrimination, including fears that radiation-related conditions could be inherited or make survivors unsuitable for marriage or employment.

Their testimony later became central to international campaigns against nuclear weapons.

Why did the United States use the bomb?

President Harry Truman and his advisers argued that using atomic weapons could force Japan to surrender without an invasion of the Japanese home islands.

American planners feared that an invasion would produce enormous casualties among Allied troops, Japanese forces and civilians.

The Allies had issued the Potsdam Declaration on 26 July, demanding Japan’s unconditional surrender and warning of “prompt and utter destruction.” The Japanese Government did not accept the terms before Hiroshima was attacked.

The decision remains one of the most fiercely debated in modern history.

Supporters have maintained that the bombings shortened the war and prevented the even greater loss of life an invasion could have caused.

Critics argue that Japan was already approaching defeat, that surrender might have been achieved by modifying its terms or demonstrating the bomb away from a populated city, and that attacking civilians with a weapon of unprecedented destructive power was unjustifiable.

The Soviet Union’s declaration of war against Japan and invasion of Japanese-held territory in Manchuria also played a significant role in the final decision to surrender.

Historians continue to disagree about the relative importance of the atomic bombs, Soviet intervention and Japan’s deteriorating military position.

Nagasaki and Japan’s surrender

Three days after Hiroshima, on 9 August, the United States dropped a second atomic bomb—“Fat Man”—on Nagasaki.

The plutonium weapon killed tens of thousands of people immediately or during the months that followed.

Emperor Hirohito announced Japan’s acceptance of the Allied surrender terms on 15 August. The formal surrender was signed aboard the USS Missouri on 2 September 1945, bringing the Second World War to an end.

Hiroshima and Nagasaki remain the only cities to have been attacked with nuclear weapons during war.

Hiroshima’s legacy

Hiroshima was rebuilt after the conflict and became an international centre for remembrance and nuclear disarmament.

The ruins of the Hiroshima Prefectural Industrial Promotion Hall, now known as the Atomic Bomb Dome, were preserved close to the explosion’s hypocentre.

Alongside the Peace Memorial Park and museum, the dome serves as a permanent reminder of the people killed and the consequences of nuclear warfare.

Every year on 6 August, a remembrance ceremony is held in Hiroshima, including a moment of silence at 8.15am.

The bombing demonstrated that a single weapon could destroy a city in seconds and leave survivors suffering for decades.

On 6 August 1945, warfare changed permanently. The destruction of Hiroshima continues to shape debates about military necessity, civilian protection, nuclear deterrence and whether humanity can prevent such weapons from ever being used again.