If you were gonna try to take out the United States with nukes, the first thing you’d need to do is take out their early warning system. It’s pretty obvious and when all the communications from NORAD went silent in Nov 1961, the US Strategic Air Command figured that an attack was coming.

They immediately prepped their missiles and sounded the alarms. Thankfully, the final order was never given, as it was discovered that a single relay station in Colorado had failed, cutting off all communications.