On October 30, 1961, the Soviet Union tested the largest nuclear bomb ever made, the Tsar Bomba. It was deployed 13,000 feet above the Barents Sea north of the USSR. The energy it released was estimated to be equivalent to 57 megatons of TNT, and sent a shockwave around the world three times.
In order to give the two planes a chance to survive – and this was calculated as no more than a 50% chance – Tsar Bomba was deployed by a giant parachute weighing nearly a tonne. The bomb would slowly drift down to a predetermined height – 13,000ft (3,940m) – and then detonate. By then, the two bombers would be nearly 50km (30 miles) away. It should be far enough away for them to survive.
Tsar Bomba detonated at 11:32, Moscow time. In a flash, the bomb created a fireball five miles wide. The fireball pulsed upwards from the force of its own shockwave. The flash could be seen from 1,000km (630 miles) away.
The bomb’s mushroom cloud soared to 64km (40 miles) high, with its cap spreading outwards until it stretched nearly 100km (63 miles) from end to end. It must have been, from a very far distance perhaps, an awe-inspiring sight.
But what was equally astonishing was that the original design was even bigger. The Tsar Bomba was scaled back from having a 100-megaton blast. That design was unworkable because it couldn't have been delivered to any target. As it was, Tsar Bomba turned its creator, Soviet physicist Andrei Sakharov, completely against nuclear weapons research and into an activist for peace and freedom. Read about Tsar Bomba and its effects at BBC Future.
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