These are scary questions, perhaps a bit too frightening for even Halloween. I know, I know, all you want is some candy or maybe to see one of your coworkers in a skimpy nurse outfit. So, without further ado:
November: This is a fun one to get us started: Two of my favorites are the training tape incident and the Belknap fire. The training tape incident occurred on November 9, 1979, when some genius at North American Aerospace Defense Command (NORAD) played a training tape showing a massive Soviet attack, lighting up the proverbial "Big Board" -- which, sadly, only exists in movies. NORAD issued warnings that went out to the entire intercontinental ballistic missile (ICBM) force and put the president's airborne command post in the air (without the president). After the event hit the press, Soviet Premier Leonid Brezhnev sent a note to Carter stating "I think you will agree with me that there should be no errors in such matters." Ah, Brezhnev, the voice of reason.) The USS Belknap incident was also pretty terrifying: a U.S. Navy cruiser in 1975 collided with an aircraft carrier and caught fire, nearly engulfing the stockpile of nuclear weapons on board.
But neither incident is as terrifying as Able Archer, a 1983 NATO command post exercise that the Soviet leadership believed might be cover for a U.S. sneak attack. Able Archer was the lowest point of the "War Scare of 1983" -- an incredibly tense period that including the Soviet shootdown of a civilian airliner, KAL 007. The scariest part? Washington had no idea how close the Russians were to doing something drastic until long afterward. When Reagan's advisers shared reports with the president detailing the depths of Soviet paranoia in early 1984, he reportedly said: "Do you suppose they really believe that?... I don't see how they could believe that -- but it's something to think about."
Reagan clearly took the lesson to heart. A few months later, in August 1984, he livened up a press conference with a little joke during sound check: "My fellow Americans, I'm pleased to tell you today that I've signed legislation that will outlaw Russia forever. We begin bombing in five minutes."
Yep. Something to think about.
December: I almost went with the 1965 incident, when an A-4E Skyhawk rolled off the USS Ticonderoga carrying a 1 megaton thermonuclear weapon, but aircraft accidents are going to be overrepresented here. (And besides, the Navy merely lost the nuclear weapon to Davy Jones's Locker. That's happened a couple of times.)
For my money, I like the Baneberry nuclear test. In December 1970, the United States conducted a 10 kiloton underground nuclear test at the Nevada Test Site, near Las Vegas. What happened underground didn't stay underground, though, venting a cloud of radioactive dust to an altitude of 10,000 feet. We still don't know what caused Baneberry to vent. I was flipping through a very dry report called The Containment of Underground Nuclear Explosions, when I came across this illustration in the front matter that offers one hypothesis.