On 7 November 1983, around 100 senior military officers gathered at Nato headquarters in Brussels to ‘fight’ World War Three. The annual simulation, known as Able Archer, came at the end of a large-scale conventional exercise ­– Autumn Forge – involving tens of thousands of Nato troops across western Europe.

Able Archer 83 was held at a time of heightened Cold War tension. Relations between Warsaw Pact and Nato-aligned nations were as bad as they had ever been. Earlier in the year, US President Ronald Reagan had branded the Soviet Union an “evil empire.” And, in September, Soviet pilots had shot down a Korean Airlines 747, killing all 269 people on board.

Meanwhile, both sides of the Iron Curtain were in the process of deploying medium range nuclear weapons – including cruise missiles based at Greenham Common in southern England – capable of striking targets within five minutes of launch. The world was on a nuclear hair-trigger.

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According to the fictional scenario behind the Able Archer 83 war game, turmoil in the Middle East was putting a squeeze on Soviet oil supplies. Meanwhile, Yugoslavia – which wasn’t aligned to either side of the Cold War – decided to back the West. The Soviet leaders in the game feared this would lead to a cascade of other eastern European countries following suit, switching allegiance from the Warsaw Pact to Nato, and putting the entire communist system at risk.