Atomic bombings of Hiroshima and Nagasaki

On 6 and 9 August 1945, the United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki near the end of World War II. These were the first and only times nuclear weapons have ever been used in battle. The bombs caused great loss of life, with many people, most of them ordinary citizens, losing their lives right away and many more suffering from serious injuries in the weeks that followed.

Before these attacks, many cities in Japan had already been heavily damaged by regular bombings from the air. The leaders of the Allies, which included countries working together to stop Germany and Japan, wanted Japan to give up the war. They warned that if Japan did not surrender, there would be even more destruction. However, Japan did not agree to stop fighting.

The two bombs dropped were part of a secret science project called the Manhattan Project. One bomb, called “Little Boy,” was dropped on Hiroshima, and another, called “Fat Man,” was dropped three days later on Nagasaki. After these attacks and when the Soviet Union also declared war against Japan, Japan finally agreed to stop fighting, ending World War II.

Today, these events are very important in understanding how the world thinks about using powerful weapons and the effects such weapons can have on people and societies. Some believe the bombings helped end the war quickly and saved more lives overall, while others feel they were wrong and should never have happened.

Background

Atomic bomb development

Main article: Manhattan Project

The discovery of nuclear fission in 1938 made building an atomic bomb possible. Concerns that a German atomic bomb project might succeed first, especially among scientists from Nazi Germany, led to the Einstein–Szilard letter in 1939. This started research in the United States. Progress sped up after the British MAUD Committee reported in 1941 that only a small amount of uranium-235 was needed for a bomb. This led to the Manhattan Project, directed by Major General Leslie R. Groves, Jr..

The Manhattan Project worked at many sites in the United States and cost over US$2 billion. J. Robert Oppenheimer led the Los Alamos Laboratory in New Mexico, where two types of bombs were developed: one using uranium-235 called Little Boy, and another using plutonium-239 called Fat Man.

Pacific War

Main article: Pacific War

In 1945, the war between the Empire of Japan and the Allies was in its fourth year. Japanese forces fought very hard, making the Allied victory costly. The United States suffered many casualties, especially in the last year of the war. President Franklin D. Roosevelt had suggested using atomic bombs on Germany earlier, but the weapons were not ready.

The Allies moved through the Pacific, recapturing areas like the Philippines and Burma. Fighting was intense, especially on Okinawa, where most Japanese defenders were killed. Japan’s resources were dwindling, and hunger spread among the people.

Preparations to invade Japan

Main article: Operation Downfall

Before Germany surrendered, plans began for invading Japan, called Operation Downfall. It had two parts: Operation Olympic to capture Kyūshū in October 1945, and Operation Coronet to take the Kantō Plain near Tokyo in March 1946. The Japanese expected this invasion and prepared to defend heavily. Predictions of casualties were very high.

Air raids on Japan

Main article: Air raids on Japan

The United States began air attacks on Japan in mid-1944 using long-range Boeing B-29 Superfortress bombers. Early attacks from China were not successful. Later, bases in the Mariana Islands like Guam, Tinian, and Saipan were captured and used for bombing.

Major General Curtis LeMay changed tactics to low-level firebombing of cities, which proved very effective. Over six months, 64 Japanese cities were firebombed. The raid on Tokyo in March 1945 was especially deadly, destroying much of the city. By mid-1945, Japan’s largest cities were devastated, and the bombing campaign continued against smaller cities.

Preparations

Organization and training

The group responsible for the missions was created in December 1944. Its job was to prepare for dropping atomic bombs on Germany and Japan. Pilots practiced dropping practice bombs on islands near Tinian and later on Japanese targets. Some missions were flown by single bombers to get Japan used to this pattern. The group had special airplanes made just for carrying these bombs, with extra features to help with the mission.

Choice of targets

Leaders chose five cities as possible targets for the atomic bombs: Kokura, Hiroshima, Yokohama, Niigata, and Kyoto. The cities were picked because they were large, important, and had not been heavily bombed yet. Hiroshima was chosen because it was a big city with hills around it that might increase the damage. Kyoto was taken off the list because of its historical importance, and Nagasaki was chosen instead.

Proposed demonstration

Some scientists thought the Allies should show the bomb’s power without hurting people first. But others felt this might not work, as Japan might not believe the demonstration or could try to stop it. There was also worry that the bomb might not work perfectly or that Japan might move prisoners of war to the test site.

Leaflets

For months, the United States dropped millions of leaflets over Japan warning civilians about air raids. These leaflets were made by recent Japanese prisoners of war and asked people to leave big cities. Even with these warnings, many Japanese stayed, and the government tried to stop people from having the leaflets.

Consultation with Britain and Canada

Before using the atomic bomb, the United States needed permission from Britain because of an agreement between the two countries. A meeting was held, and Britain agreed to let the United States use the bomb against Japan. The meeting also talked about what information could be shared with other countries.

Potsdam Declaration

After a successful test of the atomic bomb, leaders from the United States, Britain, and France demanded that Japan surrender. They said that if Japan did not surrender, they would attack and destroy Japan’s military and homeland. Japan’s government rejected this demand, saying they would keep fighting.

Bombs

The bomb called “Little Boy” was ready by early May 1945. Its parts were moved carefully to Tinian Island. Another bomb called “Fat Man” also had its parts moved to Tinian in early August.

Hiroshima

Hiroshima during World War II

Hiroshima was an important city during World War II because it had many military buildings and factories. It was a place where soldiers gathered, and it made parts for planes, ships, and weapons. The city had big buildings made of strong materials, but many houses were made of wood and easy to catch fire. Hiroshima was one of the bigger cities in Japan that had not been heavily bombed yet.

Bombing of Hiroshima

On August 6, 1945, an American plane named Enola Gay dropped a powerful bomb on Hiroshima. This was the first time a nuclear bomb was used in war. The bomb caused a huge explosion that destroyed much of the city. The blast knocked down buildings and started fires that burned for days. Many people were hurt or killed, and the city was left in ruins.

Events on the ground

People in Hiroshima saw a bright flash of light and heard a loud boom. The explosion destroyed buildings and started fires that burned everything in their path. Survivors described the scene as looking like a place from a nightmare. Many people were injured, and hospitals were overwhelmed. The city tried to organize help, but it was very difficult. The damage was so great that it took many years for Hiroshima to recover.

Events of 7–9 August

See also: Mokusatsu

After the bombing of Hiroshima, a message from the United States president warned Japan that more cities could face the same fate if they did not agree to peace terms. Radio broadcasts repeated this warning, telling people to leave big cities.

On the same day, Soviet forces began moving into areas near Japan, and Japan’s military leaders prepared to stop any attempts to end the war. Experts who visited Hiroshima confirmed that a new kind of weapon had been used. American intelligence listened to Japan’s secret messages. Leaders decided to drop another bomb, hoping Japan would agree to peace before more attacks happened.

Nagasaki

Nagasaki during World War II

The city of Nagasaki was an important seaport and industrial center in southern Japan during World War II. It produced ships, military equipment, and other war materials. Unlike other cities, Nagasaki had not been heavily bombed before because its location made it hard to find at night.

Bombing of Nagasaki

On August 9, 1945, an American plane dropped an atomic bomb on Nagasaki. This was the second atomic bomb used in war, following the bombing of Hiroshima a few days earlier. The bomb caused great destruction in part of the city, but surrounding hills limited the damage. Many people were killed, and the city’s factories and buildings were damaged.

Plans for more atomic attacks on Japan

Main article: Third Shot

After the atomic bombings of Hiroshima and Nagasaki, there were plans for more attacks on Japan. Leaders expected to have another atomic bomb ready by August 19, with even more bombs to follow in the months after. However, President Truman decided to stop using these bombs. He felt it was too terrible to hurt so many more people, especially children. The plan to keep using atomic bombs was changed, and some cities were spared from these attacks.

Surrender of Japan and subsequent occupation

Main articles: Surrender of Japan and Occupation of Japan

In August 1945, leaders in Japan were still arguing about whether to give up the war. After the bombing of two cities with powerful new weapons, the emperor decided that Japan should surrender to avoid more destruction.

The emperor told the nation that continuing the war would bring more suffering and could end Japan forever. He chose to accept the terms of the countries fighting against Japan, wanting to protect his people.

Reportage

On August 10, 1945, just after the bombing of Nagasaki, a photographer, a reporter, and an artist arrived in the city to record the damage for news reports. They took many photographs that were later published in a Japanese newspaper.

One of the first American reporters to write about what happened was Leslie Nakashima. He described how many people were still suffering and dying after the bombing. Another reporter, Wilfred Burchett, also visited Hiroshima and shared stories about the serious health problems people faced.

Later, more reports showed the terrible effects of the bombings, but some of these stories were not shared with the public right away. A documentary was made but kept private for many years. Books and artworks created by survivors helped tell the world about what happened.

Post-attack casualties

See also: Epidemiology data for low-linear energy transfer radiation, Acute radiation syndrome § History, Radiobiology, Hiroshima (book), and Terufumi Sasaki

Many people in Hiroshima and Nagasaki died in 1945 from the force and heat of the explosions. Most of these deaths happened on the days of the bombings. Others died in the months that followed because of radiation and its effects.

Doctors at the time did not understand the cause of many illnesses that appeared after the bombings. One person, Midori Naka, was the first to be officially recognized as having died from effects of radiation.

Later, scientists studied the long-term health effects on survivors. They found that radiation increased the risk of certain cancers, especially leukemia, in the years following the bombings. Studies also looked at the children of survivors and found no major increase in birth defects overall, though some specific issues were noted in a small number of cases.

Researchers continue to study the health effects on survivors to better understand the impacts of radiation exposure.

Hibakusha

Main article: Hibakusha

The people who survived the bombings of Hiroshima and Nagasaki are called hibakusha, which means "explosion-affected people." About 650,000 people are recognized as hibakusha by the Japanese government. As of March 2025, about 99,130 of these survivors were still alive, most of them in Japan. Some of these survivors have health problems because of the radiation they were exposed to.

Sadly, many hibakusha faced unfair treatment and were sometimes excluded from jobs or marriages because people were afraid of them. However, studies show that the children of survivors did not have higher rates of health issues than other children. Some survivors still feel worried or uncomfortable many years later because of what they went through.

Double survivors

A small number of people, maybe around 200, were in both Hiroshima and Nagasaki during the bombings. One man named Tsutomu Yamaguchi was in Hiroshima when the first bomb fell and then traveled to Nagasaki just before the second bomb was dropped. He was the first person to be officially recognized as having survived both bombings.

Korean survivors

During the war, many people from Korea were brought to Japan to work. Some of these people were in Hiroshima and Nagasaki during the bombings. They faced many difficulties and had a hard time getting the same help and recognition as Japanese survivors, but these issues were mostly solved by 2008.

Memorials

Hiroshima

After the war, Hiroshima faced more challenges when a typhoon damaged the city further. But the city began to rebuild with help from the government. A special law in 1949 provided money and land for rebuilding. In 1949, plans were made for a peaceful park, and a museum opened there in 1955. The city also built a tall tower as a symbol of peace.

In 1981, Hiroshima planned to place special signs at important places connected to the bombing to remember what happened. These signs include pictures and stories about those locations.

Nagasaki

Nagasaki also rebuilt after the war, changing its shape. New buildings, temples, and churches were constructed. A museum about the bombing opened in the mid-1990s.

Some parts of the destroyed city were left as reminders of the past. In 2013, four important places were protected to make sure they stay special. These places include a school building, a church bell tower, a university gate, and a shrine gate. In 2016, these places and the spot where the bomb fell were officially recognized as important historic sites.

Debate over bombings

Main article: Debate over the atomic bombings of Hiroshima and Nagasaki

People have debated for many years whether the bombings of Hiroshima and Nagasaki were right or wrong. Some believe the bombings helped end the war quickly, which may have prevented more fighting and saved lives. Others think using these powerful weapons was unfair and wrong, and that Japan might have given up even without them. There are many different opinions about what really caused Japan to surrender and whether the bombings were necessary.

Legal considerations

Main article: Aerial bombardment and international law

When World War II began, there were no clear rules about fighting from the air. The rules that existed were made before airplanes were used in war. Because of this, bombing cities with many civilians was not clearly forbidden.

Later, in 1963, a court in Tokyo looked at the bombings. The court decided that using nuclear weapons was not against the rules at that time, but it also said the bombings of Hiroshima and Nagasaki may have been wrong because they targeted cities without defenses. However, the court did not award money to those who brought the case because of an agreement between Japan and the United States.

Legacy

Main article: Nuclear warfare

After World War II, the United States built more atomic bombs and worked to improve them. Other countries also began developing these powerful weapons. By the 1980s, many nations had nuclear arms, with the United States and the Soviet Union holding the most.

In 2017, over 120 countries agreed to a treaty to ban nuclear weapons. However, Japan has not signed this treaty, though it remains protected by the United States. The use of nuclear weapons remains a serious concern around the world.