The heart of the explosion reached a temperature of several million degrees centigrade, resulting in a heat flash over a wide area, vapourising all human tissue. Unimpeded by hills or natural features to limit the blast, the fireball created by that single bomb destroyed 13 square kilometres of the city. The bomb, called ‘Little Boy’ because of its long, thin shape, was made from uranium 235.

At quarter past eight on the morning of 6 August 1945, the US plane Enola Gay dropped an atomic bomb on the city centre, a busy residential and business district, crowded with people going about their daily business. The city of Hiroshima stands on a flat river delta on the Japanese island of Honshu.