Hiroshima – The Target of the World’s First Atomic Bomb

In 1931, the Manchurian Incident triggered tensions between China and Japan and, in 1937, these tensions expanded to all-out war between the two countries. Then, in 1941, with a surprise attack on Pearl Harbour and a subsequent attack on the Malay Peninsula, Japan started the Pacific War against the United States, United Kingdom and their allies.

Factories in Hiroshima switched from producing everyday goods to making materials for the war. Rice, fuel and other everyday items were rationed. Life in the city became oppressive and many people were mobilised to the battlefields or factories. With the war growing worse, air raids over the main island on Honshu intensified and private houses were demolished to create firebreaks to protect military installations and factories from air attack.

Inspired by scientists who feared atomic bomb development by Germany, the United States had begun studying the atomic bomb when World War II began in 1939. In August 1942 the US launched a development program called the Manhattan Project.

After the spring of 1945, with Japan in an extremely weak position, the United States considered the ways of bringing the long war to an end. Their options included: invading the Japanese mainland; asking the Soviet Union to join the war against Japan; assuring continuation of the emperor system; or using the atomic bomb. The US believed that if the atomic bomb could end the war, Soviet influence after the war would be restricted and the tremendous cost of development would be justified. On July 6th, 1945, the bomb was successfully tested in a desert in New Mexico.

The potential targets for the atomic bomb were selected based on city size and potential for maximum destruction from the blast. Air raids were prohibited over these four cities – Hiroshima, Kokura, Niigata and Nagasaki. It is thought that Hiroshima became the first choice because it did not have an allied prisoners-of-war camp.

Monday the 6th of August 1945 dawned clear and sunny. At 7:31 the yellow air-raid alarm was cleared and another hot summer’s day began. At 8:15 the world’s first atomic bomb was detonated with a blinding flash about 600 metres in the air, over the Shima Hospital, and generated an enormous fireball; essentially a small sun with a temperature of more than a million degrees Celsius at its centre. The fireball reached a maximum diameter of 280 metres in one second and surface temperatures close to the hypocentre rose to between 3,000ºC and 4,000ºC. Fierce heat rays and radiation burst out in every direction, expanding the air around the fireball and creating a super-high pressure blast.

In an instant, most of the city was destroyed. Hundreds of thousands of precious lives were lost. Including residents, military personnel and civilians working in the city, it is estimated that approximately 350,000 people were directly exposed to the blast. In the final days of World War II, students in the seventh and eighth grades in Hiroshima City had been mobilised to demolish buildings for firebreaks and an estimated 6,300 boys and girls engaged in this work were killed. Death was often presumed by personal effects left behind, as many bodies were never found, identified or returned to families.

The atomic bomb used a completely different principle from that of previous weapons, one that employed a huge amount of energy released by continuous nuclear fission in an extremely short period of time. This massive destructive power enabled a single atomic bomb to instantly demolish an entire city. The bomb used on Hiroshima was delivered by three B29 bombers – one carried devices for scientific observations, another carried photographic equipment and the third was the Enola Gay, carrying the atomic bomb.

The atomic bomb, nicknamed ‘Little Boy’ was about three metres and weighed about four tons. It was initially called ‘Thin Man’ because of its long, thin design but when the actual bomb turned out to be shorter its nickname was changed. It was designed to use gunpowder to blast one piece of uranium 235 into another, in order to reach a super-critical mass instantly. Roughly 50 kilograms of uranium 235 were packed into the bomb, of which less than one kilogram instantly underwent continuous nuclear fission, releasing energy equivalent to 16,000 tons of chemical high explosives. A highly sensitive radar, attached to the bomb enabled it to explode at the altitude calculated to maximise the effects of the explosion.

As the city had previously been spared from air raids, the people of Hiroshima had no way of knowing that an atomic bomb was being dropped and some even watched the B29s drop parachutes, without running for cover. Just after the parachutes were dropped, the bomb detonated. Hanging from the parachutes were radio devices that measured the changes in atmospheric pressure and the temperatures caused by the explosion. All buildings within two kilometres of the hypocentre were crushed, burned and reduced to rubble. The clothes people wore were charred by intense thermal rays. Covered in blood, clothes in tatters, those who were able fled.

People close to the hypo centre said the atomic explosion looked yellowish red. Those farther away reported a bluish-white light resembling burning magnesium. The intense thermal rays caused burns within a radius of up to 3.5 kilometres. Those within 1.2 kilometres of the hypocentre sustained severe injuries to their internal organs and most died within a few days.

The intense heat rays from the explosion ignited wooden houses, telephone poles, and other easily combustible materials. Fires in toppled buildings were released and spread. About half an hour after detonation, these small sporadic fires melded and enveloped the entire city in a giant conflagration that consumed everything combustible. It was three days before the conflagration was, for the most part, burned out. Eighty-five percent of Hiroshima’s buildings were within three kilometres of where the bomb exploded. The damage extended to virtually the entire city, with 90 percent of all buildings burned or destroyed beyond repair.

Soon after the explosion, a giant mushroom cloud billowed upwards, carrying dirt, soot, dust and other debris high into the air. This dust and soot became radioactive, mixed with water vapour in the air, then fell back down to earth in what came to be called ‘black rain’.

Acute effects, the symptoms or injuries appearing soon after the blast which derived from heat, blast or radiation, had largely subsided by the end of December. Soon after, other disorders began to appear, including keloids, cataracts, leukaemia, malignant tumours and in-utero effects.

The atomic bomb obliterated government buildings and left communication and transportation systems dead. Yet relief activities began immediately and the very next day a plan was drawn up that involved the army, the government and citizens. The injured were given emergency treatment and transported to relief stations, corpses were cremated, and food was distributed. Any survivor who could move, including the injured, joined the crowds flocking out of the city towards the suburbs. A total of 150,000 people are estimated to have fled the city. Civil defence teams and other groups from cities, towns and villages around Hiroshima poured into the city to rescue the injured, feed the hungry and offer whatever assistance they could. Doctors and medical relief teams arrived one after the other from all over the prefecture and beyond. Meanwhile, research teams from the military and Japanese universities began to study the damage caused by the weapon.

The Army Marine Headquarters in Ujina, which had sustained little damage began rescue activities immediately. They fought the fire, rescued people and transported the injured to Ninoshima Island. A total of 53 temporary relief stations were established and 105,861 seriously injured people were admitted to such stations. Outpatient services were provided to a cumulative total of 210,048 individuals. People wrote messages on walls of schools and other buildings that were still standing regarding their whereabouts, as people searched for missing family members and friends.

Radiation affected those who entered central Hiroshima soon after the bombing and a vast number of people were poisoned by residual radiation, along with those who were exposed directly. After the bombing, Hiroshima suffered terrible shortages of medical supplies, food, clothing and shelter. Survivors were left with reduced resistance to infections and diseases, due to radiation exposure. The shock from the bomb, combined with acute physical effects, led to emotional suffering and long term anxiety. Hiroshima lost its foundations as a city. Soldiers and others returning from overseas, who had been spared from the blast, had lost their homes, workplaces and, in many cases, their families.

In the Autumn of 1945 it was said that nothing would grow in Hiroshima for 75 years. In the Spring new buds sprouted and people began to recover their hopes and courage.

A reconstruction plan was decided upon in the autumn of 1946, however a lack of financing caused delays and the Hiroshima Peace Memorial City Construction Law was passed by citizens’ vote to remedy the situation. The law granted the city access to financial support from the nation to construct the Peace Memorial Park, a hundred-metre boulevard, bridges and public housing that would serve as the basis for the rebuilding of the city.

The damage done by the bomb was so catastrophic that the conviction that humanity cannot coexist with nuclear weapons – that their use must not be allowed – became deeply rooted in the minds of the people of Hiroshima. Based on this unwavering hope for the abolition of nuclear weapons, Hiroshima  began its journey on the path to peace. On the 6th of August, 1947, the City of Hiroshima released its first Peace Declaration, mourning the victims of the A-bomb and sending a message to the people of Japan and around the world about the realisation of the abolishment of nuclear weapons and permanent world peace. Survivors of the atomic bomb began to share their harrowing experiences of the bombing, calling on the world never to use nuclear weapons again.

While the city’s reconstruction was moving forward, news related to the bombing and research on illness caused by the bomb was restricted due to occupation. Despite the people’s efforts to share their experiences, the extent of the damage and images of the survivors dealing with the aftereffects of radiation were not widely known.

After the enactment of the San Francisco Peace Treaty in 1951, efforts were gradually made by the administration to address the survivors of the atomic bomb and they themselves formed groups, demanding support. The Survivors Medical Care Law was enacted in 1957, followed by the A-bomb Survivors Special Measures Law in 1968. In 1995, these two laws were consolidated under the Atomic Bomb Survivors’ Support Law, containing measures for providing comprehensive support for health insurance, medical treatment and care.

Hiroshima Peace Memorial Museum collects and displays belongings left by the victims, photos, and other materials that graphically convey the horror of the world’s first atomic bombing. Some exhibits describe Hiroshima before and after the bombing, while others present the current status of the nuclear age. Poignant displays include a half-melted bronze Buddha, a watch stopped at 8:15am and the imprint of a dark shadow on the steps of the Sumi-tomo Bank building – the sole remains of someone who was sitting there at the time of the blast. Some of the exhibits may be too graphic for some visitors.

Opening hours: 8:30 to 18:00 from March to July and September to November, 8:30 to 17:00 from December to February and 8:30 to 19:00 in August. Entrance is 200 yen per adult.

Hiroshima Peace Memorial Museum is located in the Peace Memorial Park and can be accessed on foot from the Chuden-mae and Genbaku Dome-mae streetcar stops.


  • Information signs at the Hiroshima Peace Memorial Museum
  • http://www.pcf.city.hiroshima.jp/virtual/index_e.html
  • DK Eyewitness Japan
  • Lonely Planet: Japan
  • Wanderlust Pocket Guides – Best of: Japan

One thought on “Hiroshima – The Target of the World’s First Atomic Bomb

  • August 23, 2017 at 12:08 pm

    Such a tragic part of history, which seems now more than ever, the world hasn’t learnt from….sadly, war means money.

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Hiroshima – The Target of the World’s First Atomic Bomb

by Uncover Travel time to read: 8 min
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