THE DAY THE WORLD ALMOST ENDED.

• Position: SMOKING GUN

Since the dawn of the nuclear age, there have been dozens of narrowly missed opportunities to bring about an end to the nuclear age--along with everything else. As President Donald Trump spurns treaties meant to reduce the risk of nuclear annihilation and calls for massive spending on a dangerous new generation of weapons, let's look at some of those close calls.

NOVEMBER 5, 1956: Amid the Suez Crisis, the North American Air Defense Command (NORAD) received a series of alarming reports, including that a British bomber had been shot down over Syria and an unidentified aircraft had appeared over Turkey, which one general feared might trigger NATO's plan for nuclear strikes against the U.S.S.R. But, it emerged, the British plane was forced to land due to mechanical problems and the unidentified aircraft was a wedge of swans.

JANUARY 24, 1961: A B-52 fighter plane carrying two huge nuclear bombs broke up in midair over North Carolina, dropping its nuclear payload. A report declassified in 2013 revealed that one of the bombs--which packed about 250 times as much destructive power as the bomb dropped on Hiroshima--came close to detonating.

OCTOBER 25, 1962: In one of several potentially catastrophic events during the thirteen-day Cuban Missile Crisis, a guard at a U.S. Air Force base in Minnesota noticed a figure trying to climb a security fence and sounded an alarm to alert nearby bases. But at a National Guard base in Wisconsin, the wrong alarm sounded, causing pilots there to begin embarking on a mission to intercept Soviet attackers. The mission was called off in time; the intruder was a bear.

OCTOBER 28, 1962: On the final day of the Cuban Missile Crisis, radar operators in...