The US Air Force developed a top-secret plan to detonate a nuclear bomb on the moon as a display of military might at the height of the Cold War.

In an exclusive interview with The Observer, Dr Leonard Reiffel, 73, the physicist who fronted the project in the late Fifties at the US military-backed Armour Research Foundation, revealed America's extraordinary lunar plan.

'It was clear the main aim of the proposed detonation was a PR exercise and a show of one-upmanship. The Air Force wanted a mushroom cloud so large it would be visible on earth,' he said yesterday. 'The US was lagging behind in the space race.'