Actually my dad was stationed in the allusions just after Korea. He was a radar technician. It later became a part of
NORAD in 1958. He said then we had missiles on standby that were able to shoot down anything penetrating our airspace. I am pretty sure he said
Nike's is what they had. The problem was the relatively limited range of the missiles meant we needed a bunch every so far apart to do the job.
We also have navy ships that can shoot down in coming missiles as they cross the pond.
With our current missile technology we were able to close down a lot of the defense silos. Those of course are all secret so you never hear them spoke about. However, most of them are in the polar cap since the theory was Russia would fire over the north pole if they were to attack.