Misperception is an enduring problem in relations between people and states. The inevitable consequence of living in a world with other human beings is a constant uncertainty about the future, because we can never know what they will do; this is why we create the rule of law and political institutions that seek to give a predictability to our affairs. But the problem in international relations is more acute, because there are comparatively fewer restraints on the behaviour of other states.

During the Cold War, mankind for the first time faced a situation whereby it was possible for the actions of a few lonely men, albeit elected to high office by their fellow-citizens or sitting atop massive bureaucracies, to bring about the end of the world through a nuclear war. Even more alarmingly, routine bureaucratic processes which were under the ultimate control of no one person could trigger a chain of ever-escalating action which would place everyone in a situation that none of them wanted to be in, their hand hovering over the red button. Nuclear apocalypse was rational for no-one, and only fear and misunderstanding could ever place either side in the position of initiating it. Unfortunately, there were ample helpings on both sides.

The Cuban Missile Crisis is one such episode with which we are all familiar. Another is Able Archer 83 (it is named for the year, 1983), possibly the most famous and consequential military exercise in history.

Able Archer was an annual military exercise carried out by NATO in Europe. While we are used to thinking of the Cold War as playing out in places like Korea, Vietnam, Angola and Afghanistan, these were all sideshows to the stalemate in Europe. Such were the importance of events there that we still call it the "Cold War" despite the fact it grew hot on every other continent but this one. If there were to be a nuclear war, it would begin here. The Soviets had military superiority here, in the place they had beaten off the Nazi war machine, and U.S. military doctrine recognized this. Henry Kissinger laconically described what would happen in the event of a war in Europe thusly: "First, we lose the conventional war. Then, we lose the tactical nuclear exchange. Finally, we blow up the world".

This blowing up of the world, the nuclear apocalypse, could have come about through this kind of gradual escalation. This is what Able Archer was designed to simulate and prepare for. But the Soviets had another, long-standing fear, dating back to Stalin: that the Americans would simply launch a nuclear strike out of the blue, hoping to knock out most of the Soviets' own weapons and their leadership before a response was possible. In the late 1950s, just before the crisis in Cuba, the KGB had actually arrived at a set date on which they believed such a strike would occur. And they never stopped looking.

In the early 1980s Soviet fears had heightened. This was due to a range of factors, not least their own recent invasion of Afghanistan, which they rightly recognized had raised tensions between themselves and Washington. The election of Ronald Reagan was another factor. The Soviets knew Reagan from the presidency of Gerald Ford, when he had opposed the latter's attempts to draw closer to the Soviets and make peace with them. And now, here he was, ensconced in the Oval Office, fresh from a campaign trail in which he had oozed assertiveness, if not aggression; soon he would deride the Soviets as an "evil empire". Just a few weeks later, he announced Star Wars, an ambitious programme designed to make the U.S. immune to Soviet missile strikes.

These latter two events occurred in 1983, the same year as Able Archer 83. The history of warfare is littered with examples of military exercises being used as cover for the planning of actual aggression; the Arabs had used just such a ruse in the 1973 Yom Kippur War with Israel, and Soviet military doctrine contained plans to do just the same should they feel the need to launch a war. Knowledge of this history made the Soviets sensitive to the danger of a surprise attack masquerading as a peaceful exercise. Since the end of the Cold War, agreements between Russia and NATO mandate that military exercises by either side must allow observers from the other if they exceed a certain size; such is the enduring fear of surprise attack.

Nor could Russians easily forget Hitler's surprise attack against them in 1941, which had been the seminal political event in the youth of many of the country's leaders in 1983. The country's intelligence agencies, which had been blamed for Stalin's failures, were especially sensitive to the possibility; their sensitivity made them liable to exaggerate the threat posed by the Americans. Reagan, of course, never had any intention of launching a first strike; he professed himself shocked the Soviets could ever think that he would. But his belief had a certain naivete, for the Soviets had an understanding of the West that was built by filtering limited information through layers of propaganda and misunderstanding.

Able Archer 83 thus came at a time when the Soviets were especially sensitive to the possibility of a nuclear attack by the United States. The exercise was not how we might imagine a military exercise, with tanks sweeping across fields and infantry manoeuvring, but rather simulated what would happen at the nerve centre of NATO's military operation in the run-up to a nuclear strike. It was initially planned to even involve a co-ordinated disappearance by NATO heads of states into their nuclear bunkers, but this was cancelled out of fear that it would appear too real to the Soviets. But it did involve a simulated increase in the DEFCON level and a dry run of all the targeting, co-ordination and communication that would precede an actual nuclear strike. And all of this was visible to the Soviets.

What made Able Archer 83 different to previous exercises was the realistic nature of the simulation, and the fact that NATO were using a new, coded form of communication that the Soviets were unable to completely understand. Hence, they could see an awful lot of communications whizzing between NATO allies at the military and political level, but they could not understand what was being said. This was a recipe for unease among the Soviets, and fed a tendency for worst-case analysis among the intelligence agencies who did not want to be blamed for failing to anticipate something because of their earlier failure to crack NATO's codes.

Washington knew nothing of Moscow's fears and hence Able Archer ran its complete course. It appears that the Soviets readied nuclear bombers and it is possible they primed their missile forces for an attack. The Soviets would not have waited for the Americans to strike before lashing out themselves; they would have struck when they were convinced the Americans were about to, but before they actually had. Nuclear war is so frightening because there is a premium on striking first, delivering a knock-out blow before your enemy has even stood up. The Soviets never reached this point during Able Archer, and so its significance can be exaggerated. But it had some very real consequences.

President Ronald Reagan would later learn of how the Soviets had reacted to Able Archer, and it would cause him to modulate his policy. While the caricature of Reagan is of a warmonger, Reagan was something different and much rarer: a man who understood the relationship between peace and strength, and that in conditions of adversity, when one has an enemy, the former ultimately flows from the latter. His whole strategy of increasing tensions with the Soviets was predicated on his belief that the Soviets were rational, and that he could push them to make concessions without risking an actual war. He was genuinely shocked to learn that they had reacted to his goading so forcefully, and this influenced his turn towards moderation.

It is worth dwelling as well on what seems to be the main lesson of this event, namely the extreme capacity for destruction that nuclear weapons place in the hands of a vanishingly small minority of human beings. Decisions of war and peace are grave enough, and the intelligence that feeds them scanty and unpredictable enough, to cause concerns at the best of times. But one thing that our anti-nuclear campaigners grasp is the unforgiving nature of the nuclear weapon, the way it allows very little margin for error among those who wield its power. The campaigner's answer, unilateral disarmament, is the incorrect one, even though it seems the best because it is the easiest, as it does not require us to engage in politics or negotiation but simply to denude ourselves. In a world of ever-increasing nuclear capabilities, some answer has to be found to this conundrum: like the terrorist, the God of nuclear apocalypse only has to be lucky once.