Stanislav Petrov, a former lieutenant colonel for the Soviet Air Defence Forces, at his home in 2015. He was credited with correctly recognizing a false alarm while manning an early-warning missile defense system, thereby averting a Soviet retaliatory strike and nuclear war. (Pavel Golovkin/AP)

When alarms began to ring and a control panel flashed in front of Stanislav Petrov, a 44-year-old lieutenant colonel seated in a secret bunker south of Moscow, it appeared that the world was less than 30 minutes from nuclear war.

"The siren howled," he later said, "but I just sat there for a few seconds, staring at the big, back-lit, red screen with the word 'launch' on it." His chair, he said, began to feel like "a hot frying pan."

Col. Petrov, an official with Russia's early-warning missile system, was charged with determining whether the United States had opened intercontinental fire on the Soviet Union. Just after midnight on Sept. 26, 1983, all signs seemed to point to yes.

The satellite signal Col. Petrov received in his bunker indicated that a single Minuteman missile had been launched and was headed toward the East. Four more missiles appeared to follow, according to satellite signals, and the protocol was clear: notify Soviet Air Defense headquarters in time for the military's general staff to consult with Soviet leader Yuri Andropov. A retaliatory attack, and nuclear holocaust, would likely ensue.

Yet Col. Petrov, juggling a phone in one hand and an intercom in the other, judged that the red alert was a false alarm. Soviet missiles, armed and ready, remained in their silos. And American missiles, apparently minutes from impact, seemed to vanish into the air.

"I had a funny feeling in my gut," Col. Petrov told The Washington Post in 1999. "I didn't want to make a mistake. I made a decision, and that was it." He celebrated with half a liter of vodka, fell into a sleep that lasted 28 hours and went back to work.

While the "50-50" decision may have averted catastrophe, it ultimately destroyed the career of Col. Petrov, who died May 19 at his home in Fryazino, a center for scientific research near Moscow. He was 77.

His death — much like the defining moment of his life — was largely unreported. It was announced by Karl Schumacher, a friend and political activist who said he heard the news from Col. Petrov's son, Dmitri, and that Col. Petrov had been sick for the past six months with "an internal disease."

The colonel's brush with history came six months after President Ronald Reagan christened the Soviet Union an "evil empire," and just three weeks after Korean Air Lines Flight 007 wandered into Soviet airspace and was shot down, deteriorating U.S.-Soviet relations even further.

When NATO held a military training exercise known as Able Archer 83 that November, Soviet officials interpreted Western troop movements as preparations for a preemptive strike. The country began readying its expansive nuclear arsenal, and the West seemed primed to escalate its own efforts when an intelligence official in the U.S. Air Force, Leonard H. Perroots, chose — like Col. Petrov — not to respond to the apparent provocation. (The incident inspired the recent television series "Deutschland 83.")

Yet while Perroots was lauded at the time and went on to direct the Defense Intelligence Agency, Col. Petrov became a pariah in the Soviet military, a scapegoat for what turned out to be a case of mistaken identity in the early-warning system's software.

Instead of identifying a group of missiles, the software had spotted the sun's reflection off the top of clouds.

Col. Petrov said he was initially skeptical of the launch because only a handful of missiles had been fired — "when people start a war," he told The Post, "they don't start it with only five missiles" — and because Soviet ground-based radar had shown no evidence of an attack.

But a military investigation chastised and eventually re­assigned Col. Petrov, in large part for not keeping a detailed log of his actions during the five minutes it took him to decide the alarm was false. (His hands were full, he said.) He had also thwarted a protocol that was designed to take such a weighty decision out of the hands of humans. A computer, not an individual officer, would decide whether missiles were imminent and, thus, whether retaliatory action might be necessary.

In later years, Col. Petrov sometimes said that he was simply "in the right place at the right time." Most of his comrades, he said, would probably have confirmed the approaching missiles rather than questioned the alerts from the computer.

In fact, according to Peter Anthony, a Danish filmmaker who directed "The Man Who Saved the World," a 2014 documentary on Col. Petrov, he wasn't supposed to be there in the first place.

"Another officer was sick," Anthony said, "so Stanislav had to take over."

Stanislav Yevgrafovich Petrov was born on Sept. 7, 1939, in Chernigovka, an air base north of Vladivostok. His mother was a nurse, and his father was an aviation engineer who had flown fighter planes during World War II. He was once shot down by the Japanese, resulting in a severe head injury and an admonition to his aviation-minded son: Never fly.

When his mother became pregnant with a second child, his parents decided they could not support a family of four, and enrolled Col. Petrov in a military academy.

He studied long-distance radar systems and was stationed in the Far East, where he met his wife, Raisa, who was working as a cinema operator at a military base in Kamchatka.

Col. Petrov eventually retired from the military to care for her during her treatment for brain cancer. Reliant almost entirely on a state pension, he was reduced at one point to growing potatoes outside his apartment building to feed his family. For a time, he made soup by boiling water with a leather belt for flavor.

His wife died in 1997. In addition to his son, Col. Petrov is survived by a daughter, Yelena, and two grandchildren.

His story began attracting wide attention only in the late 1990s, after Gen. Yury Votintsev, the retired Soviet missile-defense chief, published a memoir describing Col. Petrov's previously classified role in preventing a nuclear disaster.

Until a Pravda journalist knocked on the door of the family's apartment building, Anthony said, Raisa Petrov had thought her husband was a pilot.

"Oh, your husband has saved the world from nuclear war," the reporter said, leading Col. Petrov to slam the door and, at least at first, tell his wife that the reporter had been lying.

He was, Anthony said, "afraid that he was being tested."