Thirty years ago, on October 4, 1986, a Soviet ballistic missile submarine of the 667-project class (NATO designator Yankee) caught fire while on patrol north of Bermuda, just a few hundred miles off the Eastern Seaboard of the United States. With 30 nuclear warheads aboard as well as a nuclear reactor, there were fears that the sub (the K-219) would cause a Chernobyl-style nuclear accident in close proximity to the US. Naturally, this all happened just days before a scheduled summit between Secretary General Mikhail Gorbachev and President Ronald Reagan.

But with Chernobyl only six months behind them, Gorbachev and the Soviet leadership opted for something no one might have expected—transparency. A translated document of the minutes of the Politburo published by the National Security Archives today shows Gorbachev ordered the immediate notification of the US and the International Atomic Energy Agency about the accident. As the rescue attempt was mounted, the Russian leader also called for a public release acknowledging what happened by the TASS news service.

The accident aboard K-219—which would later be made into a BBC TV movie starring Rutger Hauer as the doomed sub's captain and Martin Sheen as the captain of a nearby American sub—did not trigger a nuclear disaster largely due to the work of the sub crew. One sailor, Seaman Sergei Preminin, died after successfully shutting down the reactor, but the rest of the crew safely evacuated. The captain, Submarine Commander Captain Second rank Igor Britanov, stayed with the sub and a tow crew, but he was ordered off the sub after a tow line broke and the submarine began to sink. On October 6, it went down, surpassing its crush depth in waters over 18,000 feet deep in the North Atlantic.

In the minutes of the Politburo meeting (which was held immediately after news arrived that the submarine sank), Deputy Defense Minister Chief of Navy Admiral Vladimir Chernavin briefed Gorbachev and other party leaders. Chernavin assured everyone that there would be no nuclear explosion and that the radiation from the sub would be limited to plutonium dispersed at depth by the implosion of the missile warheads:

Specialists on the nosecone say that there won’t be a nuclear explosion. Under certain circumstances, 40 Kg of TNT may go off, but again, this will not bring about a [nuclear] explosion. The plutonium will disperse and sink. Regarding the charges, they are contained in a metal ball. After it sinks to the bottom, a corrosion process will begin which will lead to the spread of radioactivity. However it will be limited and will not reach the surface. This is a long-term process.

Answering questions about concerns that the US would try to salvage K-219 for intelligence purposes, Chernavin said that codes and other sensitive information had been taken off before everything went under. And while the concern was valid, Chernavin believed "they’ll [the Americans] take an interest in the [warheads] and the reactor’s construction. There are no new secrets there because this submarine is an older design." The one thing Chernavin thought might be of interest was the "punch cards"—likely cryptographic codes—which were not removed because they were in "a special safe."

Gorbachev responded to the briefing by reiterating his previous instructions on transparency while also trying to head off a US salvage attempt:

Further, as I already said, it is important to get a message about what has happened to the socialist countries, the Americans, the IAEA, and make a report via TASS. Herewith it is necessary to specify that there is no threat of a nuclear explosion or nuclear contamination. To prevent the Americans from raising the submarine we should say that we are developing organizational and technical measures connected with further steps related to what has occurred.

Five days later, Gorbachev would meet with Reagan. After the nearly apocalyptic events around the Autumn Forge "war scare" in 1983, both were eager to step back from the brink and begin nuclear arms talks. Gorbachev's embrace of glasnost helped raise the level of trust between the leaders. And while they did not reach an immediate breakthrough, the talks set the stage for the Intermediate-Range Nuclear Forces Treaty signed a year later.