The North American black bear (ursus americanus) is the smallest of the continent's 3 bear species, and (comparatively) the most docile. It generally prefers to avoid humans and be left alone.
It was the Cuban missile crisis. The 2 superpowers were locked in a potentially lethal stare-down that affected lives across the globe. Both were on a hair trigger, watching for the other to make the first move.
Volk Field, in Wisconsin, wasn't one of America's larger bases. It was primarily used for pilot training and didn't even have a control tower. Planes were directed from a command center at Duluth.
In the current state of readiness, though, the Air Force had dispersed American warplanes to many such small bases across the north. Tensions were high. There was fear that Soviet agents would try to destroy the planes or runways prior to a first strike. Extra alarms had been hurriedly rigged up everywhere, alongside the dreaded klaxon that meant "launch nuclear bombers." Armed sentries patrolled constantly.
There were no drills. The pilots and planes were ready. The men had been told that, given the world situation, if the alarm sounded it was the real thing.
It was around midnight when a sentry patrolling the Duluth command center noticed a figure just outside the security fence. As he approached, it suddenly began climbing the fence, trying to get into the restricted area. This might be it. A Russian spy, trying to sabotage the bases to let the Soviets get in a first nuclear strike.
The guard fired his gun at the figure and hit the alarm button that warned of a ground intruder. The trespasser jumped off the fence and ran back into the forest on all fours- a large black bear. But the sabotage alarm had now been activated at all the bases under Duluth's command, sending armed guards racing to protect the planes.
Except at Volk Field.
Due to an undetected wiring error when the base was hurriedly readied for bombers, the nuclear war klaxon sounded there.
Fighter crews scrambled to planes. Their mission (likely one-way) was to intercept long-range Soviet bombers coming over the North Pole. Aside from other weapons, each American plane carried a single AIR-2 "Genie" rocket with a 1.5 kiloton nuclear warhead to be used against enemy formations. The Russians, once they detected American planes heading for them, would certainly retaliate in kind.
They taxied down the runway to Armageddon. Once airborne they couldn't be recalled- they were under orders to assume any ground communication telling them to come back was from the enemy. There was no control tower to correct the error before they took off.
A quick-thinking officer in the base's command center called Duluth, and learned of the mistake. There was no war, only an errant bear. He hurriedly jumped into a truck, turned on the flashing lights, and drove onto the runway, blocking the fighters from taking off and alerting them to the mistake. He was able to stop them just in time.
It was another close call.
Those involved didn't even know what had happened for another 25 years, when the incident was officially declassified.
Life on the edge is scary.