The great fear of nuclear weapons bombarding schools, churches, and homes in the 1980s was not one-sided. While American schoolchildren were scurrying under desks in “duck-and-cover” drills, Soviet citizens were bombarded by government reminders on the radio and television that an American attack could come at any time.
During this period of mutual terror, NATO held regular war games. One annual event was Able Archer, a command post exercise in Western Europe that tested the ability of NATO to respond to a nuclear attack. In 1983, a particularly realistic iteration of the event nearly triggered an actual nuclear war.
In Able Archer 83 and related exercises held in the same time period, NATO had upped the ante by including more units and by airlifting 19,000 troops to Europe to participate. They ordered that planes “readied” for a strike in the exercise be actually taxied out of the hangars with dummy warheads attached.

And, most alarming for the Russians, the exercise called for a simulated release of nuclear weapons. The Warsaw Pact had long predicted that the Americans would make the first move in a nuclear exchange and that they would do so by camouflaging the action as a war game.
To them, Able Archer 83 seemed like the perfect cover for an actual attack, and they readied their forces to respond or possibly attack preemptively.
They increased their reconnaissance flights, targeting areas that would show troop buildups or nuclear preparations. Nuclear warheads were placed on bombers, ballistic missile crews were placed on high-alert, and Soviet submarines were sent into the Arctic to ensure the Soviets could retaliate or, if they saw any signs of a strike, they could fire first.
Modern intelligence reviews of the exercise, the Soviet response, and information gleaned from spies indicates that the Soviets truly thought that Able Archer 83 was an attack.
A British spy in the KGB, Col. Oleg Gordievsky, said that about a week into the exercise, the KGB sent out a cable alerting KGB officers that the American military had just elevated their alert level and that the countdown to war may have already started.
Gordievsky alerted London to the risk the West was running in the exercise and London lobbied America to take steps to prevent a disaster.

Luckily, nothing in Able Archer 83 pushed Soviet fears over the edge and Russia never launched a preemptive strike. Reagan, who later met Gordievsky in the Oval Office after the spy defected to England, wrote that he thought someone should tell the Soviets directly that America had no intention of launching a first strike.
Otherwise, he feared the Soviets were so “defense-minded, so paranoid about being attacked” that they might launch a nuclear strike just to avoid suffering one.