In the mid-1980s, the Soviet Union had a computer program that helped it decide when to launch a nuclear war

This week, the National Security Archive at George Washington University published a newly declassified 1990 US intelligence community study that revealed terrifying details about the 1983 US-Soviet war scare.

The report found the US and Soviets came unnervingly close to going to war in 1983 after the US conducted a large-scale military exercise in central Europe called Able Archer.

The Soviets incorrectly suspected the US was using the exercise as a cover for a real nuclear first-strike. The report found the US missed nearly every sign that the Soviets were serious about going to war in order to preempt such an attack.

The report is full of unpleasant surprises about the state of the world during the Cold War. It documents how fear of an American first-strike within the Soviet Union morphed into a kind of corrosive conventional wisdom that war was actually imminent - a fear that nearly became self-fulfilling in late 1983.

But the strangest part of the report has to do with how the Soviets convinced themselves they were so vulnerable. It turns out that Soviet leaders' assessment of their strategic balance with the US was partly created through a KGB-operated computer program called VRYAN, a Russian acronym for "Surprise Nuclear Missile Attack," according to the report.

As the report puts it, "During the war scare [the Soviets] were highly dependent on a computer model." VRYAN used a "database of over 40,000 weighted elements" to identify "inherently unstable political situations in which a deterioration of Soviet power might tempt a US first strike."

Over 200 KGB employees were responsible just for "inserting fresh data" into the system. This data consisted of military, political, and economic-related information that could indicate if conditions were ripe for a US nuclear attack. Much of the data consisted of classified information that came from all over the Soviet government.

The size and scope of VRYAN indicates its importance within the Soviet Union's threat assessment infrastructure during the war scare. Its purpose was to sort through the noise of global and domestic affairs and produce a single number value for the Soviet Union's power relative to the US. The US' power would be expressed as 100; VRYAN would assign the Soviet Union a number representing Moscow's strength as a percentage of US strength.

According to the report, the Soviets believed that if VRYAN produced a value of 60 or higher, the Soviet Union was strong enough to prevent the US from undertaking a nuclear first strike, with 70 representing a "desirable margin." The "critical threshold" was 40: "Below this level, the Soviet Union would be considered dangerously inferior to the United States," the report reads. "[Redacted] if the Soviet Union ever fell below forty percent, the KGB and the military leadership would inform the political leadership that the security of the USSR could not be guaranteed."

At that point, the Soviet leadership would have a semi-automated green-light for nuclear war: "[Redacted] the USSR would launch a preemptive attack within a few weeks of falling below the 40% threshold."

By 1984 - amid a flailing war in Afghanistan, frozen relations with the US, and a declining economy - VRYAN was producing values of 45%, perilously close to the point where Soviet decision-makers could begin to contemplate a preemptive nuclear strike.

As the report notes, it's unclear what role VRYAN actually played in Soviet decision-making. The program "apparently was not tied to any military operational plans," according to the report. There's also no sign of the Politburo acting on its conclusions.

But the report ominously notes that Politburo security decisions in the early 1980s were in the hands of a very limited number of people. The computer program only had to convince the majority of a small high-level clique in order to contribute to a push towards war.

The report suggests the most important role of VRYAN was to confirm the existing biases of the Soviet security establishment.

The entire computer program was built on the assumption that the US would take advantage of the Soviet Union's weaknesses to launch a nuclear first-strike. Its role wasn't to assess if the US was willing to start World War III. It was to figure out when the US would be likeliest to launch it.

And that's not the system's only analytical leap. VYRAN seemed to connect Soviet vulnerability to a nuclear first-strike to the US' desire to actually launch one, a causal connection that even a small army of analysts would have difficulty proving.

At the time VRYAN was set up, the Soviet Union was in fact vulnerable in the event of a US nuclear attack and was seeing its hypothetical second-strike capabilities fade in light of the US's increasing military strength. But that doesn't mean the US would actually have attacked the Soviet Union.

VRYAN shows how anxiety about the Cold War strategic balance mutated into a fateful misunderstanding of the enemy's intentions, to the point where an elaborate computer program reinforced the Soviet Union's system-wide paranoia.

The story of VRYAN, and the larger report, is a chilling portrait of a country's leadership convincing itself they're in existential danger - and building both machinery and actual policy around that assumption.

The irony is that the Soviet Union really was in existential danger. By 1991, unsustainable military spending, US geopolitical pressure, plunging quality of life, the fall of Moscow-dominated communist regimes in eastern Europe, and the stagnation of the country's political and economic order had destroyed the Soviet Union.

And the US didn't have to fire a single nuclear weapon.