Able Archer 83 was a NATO nuclear command post exercise that the Russians almost mistook for the real thing — a U.S. first strike. And when President Reagan learned about this, it stuck on his conscience. It may have been a turning point in the Cold War. About the same time as Able Archer, Reagan received his first briefing of the nuclear war plans, and was told that a winnable nuclear war would cost at least 60 million lives. And he watched, along with millions of Americans, a made-for-TV movie about the horrific aftermath of a nuclear apocalypse.

Today, Nate Jones at the National Security Archive at George Washington University has published a treasure trove of previously classified documents about the frenetic months leading up to Able Archer, including the handwritten notes of a conversation that former U.S. Ambassador to the Soviet Union Averell Harriman had with Soviet Premier Yuri Andropov, classified CIA and NSA histories about war tensions, new recollections from Soviet officials who opened up to archivists in the 1990s, and detailed information about the psychological operations campaign that may have stoked Soviet fears about U.S. intentions.

Historians today question whether Russia really believed that Reagan intended to strike first, but as the evidence sees the light of day, it is hard to avoid that conclusion, even factoring in propaganda and the well-reported paranoia of the Soviet leadership.

The scary thing is that the United States national security establishment either ignored or did not believe the extent to which Russia was genuinely afraid. It took incidents like Able Archer to convince Reagan that nuclear brinksmanship was something that he could not leave to the interagency policy-making apparatus. It was too important; he had to take the reins himself. He was the still the Cold Warrior that history remembers, but from that moment on, he had a laser-like focus on preventing nuclear catastrophe. It was, in some senses quite literally, a religious mission.