Using the bomb: First tests - Hiroshima

To calibrate atomic explosion measuring instruments, a test with 108 tonnes of TNT was carried out on 7 May 1945.

The A bomb

On 12 July, 1945, at 5.30 am, on the Trinity site, the first atomic bomb in history exploded, releasing energy equivalent to the explosion of about 20,000 tonnes (20 kt) of TNT. The mushroom cloud rose to an altitude of 12 km.

This huge explosion brought home to the scientists the fact that they had manufactured the most frightful device of the Second World War, and many of them would try to prevent its use. Alas, the politicians and the military, for various reasons, would go on to launch these bombs on two Japanese cities: Hiroshima and Nagasaki. 


On 6 and 9 August, two bombs were dropped: Little Boy on Hiroshima and Fat Man on Nagasaki. They caused enormous damage and human loss (80,000 direct deaths in Hiroshima, 60 00 in Nagasaki), which prompted Japan to put an end to the war against the United States.

Explosion of the first atomic bomb - Trinity

Imprimer Using the bomb: First tests - Hiroshima

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