The revelations aren’t mere details of history; they also hold relevant lessons for how leaders should think and act in ongoing crises in hot spots around the world today.

The documents, released this week by the State Department historian’s office, focus on a massive military training exercise known as Able Archer, in which NATO simulated the transition from conventional to nuclear conflict in the event of a war in Europe.

It turned out, top Soviet leaders thought that the war game was real—that the U.S. and NATO really were about to launch a nuclear first strike against the USSR—and top Soviet military commanders took steps to retaliate.

In one of those steps, the new documents reveal, the commander of the Soviet 4th Army Air Forces in Eastern Europe ordered all of his units to make “preparations for the immediate use of nuclear weapons.” As part of that order, crewmen loaded actual nuclear bombs onto several combat planes.

Much about the Able Archer war game was first made public just six years ago, when, after more than a decade of legal battles, the National Security Archive, a private research organization, obtained a lengthy, extremely classified U.S. intelligence report detailing exactly what NATO forces did, and how Soviet commanders responded, during the exercise.

But the fact that the Soviets armed their aircraft with nuclear bombs—a discovery based on U.S. and British intelligence intercepts of Soviet communications at the time—has not been declassified until now. The new fact elevates to a higher level the danger that the world briefly faced, even though—unlike with other nuclear near misses, such as the Cuban missile crisis—almost nobody knew it at the time.

The Able Archer crisis might not have been a near miss—it might easily have escalated to a shooting war—had it not been for a single American officer, Lt. Gen. Leonard Perroots, the intelligence chief for U.S. Air Forces in Europe, who saw the Soviet moves, interpreted them correctly, and stopped what might otherwise have been a deadly escalation.

Most U.S. officers viewed Able Archer as a typical war game, nothing that would throw Soviet officers into a panic. But Perroots saw that, in fact, it was something different. It was a lot bigger than most of these games, involving a fleet of cargo transport planes flying 19,000 soldiers in 170 sorties from the United States to bases in Europe. And it was more realistic as well. The cargo planes maintained radio silence. B-52 bomber crews taxied their planes to their runways and loaded them with dummy bombs that looked remarkably real. The Strategic Air Command raised its nuclear alert levels to the highest level. The Soviets were monitoring all of this, of course, as they generally did and as the U.S. commanders knew they would. But they reacted in ways that they never had before—in ways similar to how they might have acted if the U.S. were gearing up for a real attack—including, as we now know, loading nuclear bombs on aircraft in Eastern Europe.

Ordinarily, when the Soviets took such actions, U.S. intelligence agencies would notify senior military officers, either on the scene or back in Washington, who would respond with similar actions, if just to let the Soviets know that we were watching what they were doing and were ready to repel an attack.

When Perroots informed his boss, the commander in chief of U.S. Air Forces in Europe, Gen. Billy Minter, of the Soviets’ “unusual activity” at the start of Able Archer, Minter was about to respond in the usual way, but Perroots advised him to hold off. He recognized that the Soviets were probably reacting to what we were doing—and any further escalation on our part would worsen the situation, might even trigger war. Let’s wait and see what happens next, he suggested.

Ordinarily, when the Soviets took such actions, U.S. intelligence agencies would notify senior military officers, either on the scene or back in Washington, who would respond with similar actions, if just to let the Soviets know that we were watching what they were doing and were ready to repel an attack.

When Perroots informed his boss, the commander in chief of U.S. Air Forces in Europe, Gen. Billy Minter, of the Soviets’ “unusual activity” at the start of Able Archer, Minter was about to respond in the usual way, but Perroots advised him to hold off. He recognized that the Soviets were probably reacting to what we were doing—and any further escalation on our part would worsen the situation, might even trigger war. Let’s wait and see what happens next, he suggested.

And indeed, after Able Archer ended a few days later and the thousands of American troops flew home and SAC lowered its nuclear alert, the Soviets unloaded their bombs and canceled their nuclear alert as well.

One of the newly declassified documents is a memo that Perroots wrote in 1989, as he was retiring from his final career post as director of the Defense Intelligence Agency, detailing what he’d seen and done during Able Archer six years earlier. The National Security Archive has long been trying to obtain the Perroots memo; DIA officials have told the archive’s lawyers that the memo was lost. On their own initiative, State Department historians found it in a file at the CIA.

The Able Archer near miss did come to have consequences—in a good way. While the war game was unfolding, Oleg Gordievsky, a London-based KGB officer who had turned double agent, was providing his British handlers in MI6 with documents revealing that Soviet officials were viewing the exercise as a prelude to an attack by the United States and NATO. The British, as was customary, shared the intelligence with their American cousins. At first, and for more than a year after, the CIA’s top officials were skeptical, dismissing the Soviets’ “war scare” as “propaganda,” designed to inflame anti-American sentiment in Western Europe.

But President Ronald Reagan took the war scare seriously. Just days after the wrap-up of Able Archer, his national security adviser, Robert “Bud” McFarlane, showed him Gordievsky’s reports, which Reagan read with—as McFarlane recalled years later—“genuine anxiety.”

Reagan had been pushing hard against the Kremlin, hoping the pressure might bring down the Soviet system. In 1981, his first year in office, an armada of 83 U.S., British, Canadian, and Norwegian ships sailed near Soviet waters, undetected. In April 1983, seven months before Able Archer, 40 U.S. warships, including three aircraft carriers, approached Kamchatka Peninsula, off the USSR’s eastern coast, maintaining radio silence and jamming Soviet radar. As part of the operation, Navy combat planes simulated a bombing run over a military site 20 miles inside Soviet territory. An internal NSA history noted, “These actions were calculated to induce paranoia, and they did.”

Still, as Reagan read the Gordievsky report, “it did bother him,” McFarlane later recalled, that the Soviets would seriously entertain “the very idea” that he would launch a nuclear first strike. On Nov. 18, 1983, one week after Able Archer was over, he wrote in his diary, “I feel the Soviets are so defense minded, so paranoid about being attacked that without being in any way soft on them we ought to tell them no one here has any intention of doing anything like that.”

The same day, Reagan met with his secretary of state, George Shultz (who died this month at the age of 100), to discuss setting up a back channel of communication with Moscow. The next morning, 12 senior officials met for breakfast in Shultz’s dining room at the State Department to discuss reopening long-moribund talks with Moscow—a topic so sensitive at the time that Shultz told them not to tell anybody that the meeting had even taken place. Two months later, on Jan. 16, 1984, Reagan gave a televised speech. The key line—a dramatic departure from previous pronouncements on the Soviet Union as an “evil empire”—was this: “If the Soviet government wants peace, then there will be peace. … Let us begin now.”

He had to wait a little while. Two Soviet leaders, Yuri Andropov and Konstantin Chernenko, died while Reagan’s diplomats tried to arrange meetings. But then came Mikhail Gorbachev, a genuine reformer, looking for peace with the West so he could finance his politico-economic perestroika, and, soon enough, the Iron Curtain shattered and the Cold War ended.

This might not have happened if Reagan hadn’t realized, in the wake of Able Archer, that his belligerent rhetoric and aggressive actions had gone too far—that he had to dial things back and see if the two countries might get along, before their myriad causes for mutual distrust unleashed catastrophe.

In some ways, the world today is less fraught with ultimate danger than it was 38 years ago. There is no cause for fear of a massive nuclear attack by or against the United States, Russia, or, really, any other country. But at the same time, the world is more densely laced with hot spots that could erupt into war, and war zones that could spread like lethal firestorms, and there are fewer power blocs—no real “superpowers,” in the sense that the term once meant—that might contain the conflagration. Intelligence is scanty or ambiguous about many of these potential crisis areas. Assumptions about an adversary’s ambitions or odd actions can more easily harden into dogma.