On the morning of Monday 6 August 1945 – 70 years ago today – the residents of the Japanese city of Hiroshima awoke to a bright and warm summer’s day. An air raid warning sounded at around 07:00, but no bombs fell and the all-clear was given an hour later. Father John John A Siemes, a philosophy professor, was sitting in his room 2 km away from the city: ‘Suddenly – the time is approximately 8:14 – the whole valley is filled by a garish light which resembles the magnesium light used in photography, and I am conscious of a wave of heat’ (CAB 126/252). Other eye-witnesses ‘saw a blinding white flash in the sky, felt a rush of air and heard a loud rumble of noise, followed by the sound of rending and falling buildings. All also spoke of the settling darkness as they found themselves enveloped by a universal cloud of dust’ (PREM 8/194). An atomic bomb had exploded above their city.