Kennedy was right to worry. To hear Vadim Orlov, an intelligence officer onboard the B-59, tell it, the depth charges sounded less less like a warning than like war itself. “They exploded right next to the hull,” he wrote years later. “It felt like you were sitting in a metal barrel, which somebody is constantly blasting with a sledgehammer. … We thought—that’s it—the end.” Orlov said the barrage of explosions prompted the submarine’s captain, Vitali Savitsky, to panic. Unable to make contact with Moscow for several days, Savitsky had not been notified of the United States’ intent to employ practice depth charges as part of its Cuban blockade. Convinced all-out conflict had broken out, he ordered the B-59’s nuclear torpedo to be assembled for launch. “Maybe the war has already started up there, while we are doing somersaults here,” Savitsky said, according to Orlov’s account. “We’re going to blast them now! We will die, but we will sink them all—we will not disgrace our navy!”

It didn’t matter that the B-59 was incommunicado—Moscow had already authorized the vessel to launch the torpedo if deemed necessary. Still, protocol required Savitsky to get unanimous agreement from two others on board before the order could take place: his deputy political officer, Ivan Maslennikov, and his second-in-command, Arkhipov.

Maslennikov said yes. Arkhipov said no.

Though it’s impossible to know exactly what would have taken place if Arkhipov wasn’t onboard the B-59 that day, it’s not hard to imagine. For one, the submarine likely wouldn’t have returned to the surface (where it would have been met not with an outbreak of war, but with a U.S. destroyer that would have ultimately allowed the vessel to return back toward Russia). Instead, Savitsky’s order to launch the torpedo would have been followed, leading to the destruction of one of the U.S. vessels surrounding the submarine—an act of aggression that, as Russian archivist Svetlana Savranskaya noted, would have sparked a chain reaction almost certainly leading to “global nuclear war.”

“We were extremely lucky that Vasili Arkhipov happened to be the guy who was there,” Max Tegmark, the president of the Boston-based Future of Life Institute (FLI), told me at an event honoring Arkhipov with FLI’s inaugural Future of Life award Friday in London. “Vasili Arkhipov is arguably the most important person in modern history, thanks to whom October 27, 2017 isn’t the 55th anniversary of WWIII. We’re showing our gratitude in a way he’d have appreciated, by supporting his loved ones.”

Though the award was being bestowed posthumously to Arkhipov, who died at the age of 72 in 1998, Tegmark said FLI managed to track down Arkhipov’s daughter, Yelena Andriukova, and grandson, Sergei Andriukova, who accepted the award in London on his behalf. When I asked Sergei what his grandfather told him about the experience, he said he didn’t learn the full story of what happened until 2000, two years after his grandfather’s death. “He never said a word to his family because it was closed, secret information—he wasn’t allowed to talk about it,” he told me through an interpreter. “For many years he was collecting photographs, writing notes, writing down his memories, and when the members of the family asked him, ‘Why are you doing this?,’ he would always answer, ‘I can’t tell you now, but one day you will know.’”