Hiroshima

Hiroshima, Japanese city, situated some 800 km. (500 mi.) from Tokyo, on which the first operational atomic bomb was dropped at 0815 on 6 August 1945 (see Nagasaki for the second). Nicknamed ‘Little Boy’—a reference to Roosevelt—the bomb was 3 m. (9 ft. 9 in.) long, used uranium 235, had the power of 12.5 kilotons of TNT (see explosives), and weighed 3,600 kg. (nearly 8,000 lb.).

Much discussion by a Target committee had preceded the decision to make Hiroshima the first target. To be able to assess the damage it caused, and to impress the Japanese government with the destruction it was expected to wreak, it was necessary to choose a city that had not yet been touched by the USAAF's strategic air offensives. Kyoto was also considered but its unrivalled beauty ruled it out.

The bomb was delivered by a US B29 bomber, nicknamed Enola Gay, from the Pacific island of Tinian. Dropped by parachute it exploded about 580 m. (1,885 ft.) above the ground, and at the point of detonation the temperature probably reached several million degrees centigrade. Almost immediately a fireball was created from which were emitted radiation and heat rays, and severe shock waves were created by the blast. A one-ton (900 kg.) conventional bomb would have destroyed all wooden structures within a radius of 40 m. (130 ft.). Little Boy destroyed them all within a radius of 2 km. (1.2 mi.) of the hypocentre (the point above which it exploded). The terrain was flat and congested with administrative and commercial buildings, and the radius of destruction for the many reinforced concrete structures was about 500 m. (1,625 ft.), though only the top stories of earthquake-resistant buildings were damaged or destroyed. Altogether an area of 13 sq. km. (5 sq. mi.) was reduced to ashes and of the 76,000 buildings in the city 62.9% were destroyed and only 8% escaped damage.

Within 1.2 km. (.74 mi.) of the hypocentre there was probably a 50% death rate of the 350,000 people estimated to have been in Hiroshima at the time. Hiroshima City Survey Section estimated a figure of 118,661 civilian deaths up to 10 August 1946 (see Table ). Add to this a probable figure of 20,000 deaths of military personnel and the current figure—for people are still dying as a result of the radiation received—is in the region of 140,000. Among those who survived, the long-term effects of radiation sickness, genetic and chromosome injury, and mental trauma have been catastrophic, even unborn children having been stunted in growth and sometimes mentally retarded.

Hiroshima: Total number of civilian casualties due to the atomic bomb dropped on Hiroshima up to 10 August 1946

Bibliography

Committee on Damage by Atomic Bombs in Hiroshima and Nagasaki, Hiroshima and Nagasaki: The Physical, Medical, and Social Effects of the Atomic Bombings (London, 1981).