As America tested the first hydrogen bomb - capable of flattening entire cities - the Cold War entered a new and deadly phase, with the Soviets, America and Britain racing to build weapons of mass destruction (including secret tests of deadly nerve agents) - and the Doomsday Clock set to two minutes to midnight for the first time. Guy Walters talks to author Roger Hermiston about why 1953 could have spelt the end of the human race.

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