Hiroshima
The aftermath of the atomic bomb dropped on Hiroshima, Japan, by the US at the end of World War II GETTY

On 6 August 1945 the United States dropped an atomic bomb nicknamed Little Boy on the city of Hiroshima in Japan. The fission of slightly less than one kilogram of uranium-235 released energy equivalent to around 15,000 tonnes of TNT, flattening five square miles of the city in seconds.

Yet despite the devastation the two bombs unleashed, they are far from the most powerful nuclear weapons ever built. From the first hydrogen device to the Soviet Union’s detonation of a weapon with 1,400 times the combined power of Hiroshima and Nagasaki, more than 2,000 nuclear tests have been carried out since 1945.

1945: Beginning of the nuclear age

The US government tested its first nuclear weapon, code-named Trinity, in the Jornada del Muerto desert in New Mexico on 16 July 1945. Marking the beginning of the nuclear age, the flash light from the blast – which measured 20 kilotons of TNT – was seen across New Mexico as well as parts of Arizona, Texas and Mexico. Trinity was an implosion-design plutonium device, the same design of weapon that would later be used to devastate Nagasaki.

After witnessing the blast, Julius Robert Oppenheimer, one of the key physicians in the Manhattan Project, later said he recalled a verse from the Hindu text, the Bhagavad Gita. He translated it as: “I become death, the destroyer of worlds.”

Nagasaki bomb

The radioactive plume from the bomb dropped on Nagasaki City seen from 10km away in Koyagi-jima, Japan GETTY