The US military uses a scale of alert readiness called DEFCON, with DEFCON 5 being the lowest alert level and DEFCON 1 being the highest, preparing for imminent nuclear war. At least once during the Cold War, readiness was pushed all the way to DEFCON 2.

When DEFCON levels were raised, how secret was this? Did the Soviet Union know when DEFCON levels changed?

  • I imagine if their spies were unable to tell them the exact state that they would notice the increased activity, or be able to make a pretty good guess as it would have been their actions causing those responses.
    – Ryathal
    Commented Jan 23, 2013 at 20:49
  • 1
    @Ryathal: But would going from, say, 5 to 4 result in extra activity discernible to an outside observer? Commented Jan 23, 2013 at 20:57
  • @FelixGoldberg after a quick glance at Wikipedia's description of differences a 5 to 4 would probably have been unnoticed (and many places were always at 4), but others definitely would have noticed the difference between other levels especially the USSR
    – Ryathal
    Commented Jan 23, 2013 at 21:09
  • @FelixGoldberg AFAIK at no point was the US ever at DEFCON 5 prior to the collapse of the USSR, so that's a moot point. The other levels all include marked differences in the deployment of military forces and can thus be detected easily.
    – jwenting
    Commented Jan 24, 2013 at 9:37
  • @jwenting: Actually, 5 is the lowest level, so you must have meant 1. But apart from that I guess you're right. Commented Jan 24, 2013 at 10:16

1 Answer 1


Sometimes it deliberately wasn't kept secret from the enemy. This is from William Taubman's Khrushchev: The Man and His Era, about the Cuban missile crisis in 1962:

At 10:00 A.M., Washington time, when the quarantine went into full effect, the U.S. strategic Command moved from Defense Condition 3 to DEFCON 2, one level below that of general war. For the first time in history all American long-range missiles and bombers were now on alert, and scores of planes loaded with atomic bombs were aloft around the clock, refueled by areal tankers, waiting over Greenland and northern Canada for the signal to proceed toward the assigned Soviet target. To make sure Moscow noticed, the SAC commander, General Thomas Power, took it upon himself to "announce" the move in uncoded message to his men.

A footnote identifies the following source for the last sentence:

Laurence Chang and Peter Kornbluh, eds., The Cuban Missile Crisis, 1962: A National Security Archive Documents Reader (New York, New Press, 1992), p. 371.

An "announcement" would also seem to make sense under the logic of nuclear deterrence. I can't confirm whether Power's communication contained the verbatim phrase DEFCON 2, but perhaps it did, because at this point (one hopes) nobody wanted to issue ambiguous commands.

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