In 1957, Britain exploded its first megaton hydrogen bomb - codenamed Operation Grapple X. It was the culmination of an extraordinary scientific project, which against almost insuperable odds turned Britain into a nuclear superpower. Featuring access to the top-secret nuclear research facility at Aldermaston, the programme features interviews with veterans and scientists who took part in the atomic bomb programme, some speaking for the first time, and newly released footage of the British atomic bomb tests.