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On the morning of 30 October 1961, a Soviet Tu-95 bomber took off from Olenya airfield in the Kola Peninsula in the far north of Russia.

The Tu-95 was a specially modified version of a type that had come into service a few years earlier; a huge, swept-wing, four-engined monster tasked with carrying Russia’s arsenal of nuclear bombs.

The last decade had seen enormous strides in Soviet nuclear research. World War Two had placed the US and USSR in the same camp, but the post-war period had seen relations chill and then freeze. And the Soviets, presented with a rivalry against the world’s only nuclear superpower, had only one option – to catch up. Fast.

On 29 August 1949, the Soviets had tested their first nuclear device – known as ‘Joe-1’ in the West – on the remote steppes on what is now Kazakhstan, using intelligence gleaned from infiltrating the US’s atomic bomb programme. In the intervening years, their test programme had surged in leaps and starts, detonating more than 80 devices; in 1958 alone, the Soviet tested 36 nuclear bombs.

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But nothing the Soviet Union had tested would compare to this.

The Tu-95 carried an enormous bomb underneath it, a device too large to fit inside the aircraft’s internal bomb-bay, where such munitions would usually be carried. The bomb was 8m long (26ft), had a diameter of nearly 2.6m (7ft) and weighed more than 27 tonnes. It was, physically, very similar in shape to the ‘Little Boy’ and ‘Fat Man’ bombs which had devastated the Japanese cities of Hiroshima and Nagasaki a decade-and-a-half earlier. The bomb had become known by a myriad of neutral technical designations – Project 27000, Product Code 202, RDS-220, and Kuzinka Mat (Kuzka’s Mother). Now it is better known as Tsar Bomba – the ‘Tsar’s bomb’.