On September 26th, 1983, Lieutenant Colonel Stanislav Yevgrafovich Petrov was the officer on duty when the warning system reported a US missile launch. Petrov kept calm, suspecting a computer error.
Then the system reported another US missile launch.
And another, and another, and another.
What had actually happened, investigators later determined, was sunlight on high-altitude clouds aligning with the satellite view on a US missile base...
Go read the whole thing. And hoist a glass to Lt. Col. Petrov tonight in gratitude for not vaporizing us all.
Akubra tip to Mark Shea.