In 1978 and 1983 two Korean civilian planes were shot down after entering Soviet airspace. After 1983 disaster, Reagan record his "Address to the Nation on the Soviet Attack on a Korean Airliner".
In this video, he said: "Commercial aircrafts from Soviet Union and Cuba, on a number of occasions, have overfllown sensetive United States military facilities. They were not shot down".
Is this really happened? And how US military respond to this situatuions?
Quite often, they did run a airline service to New York after all.
The problem is that much of the USSR's airspace was closed to civilian traffic, you could only fly in specific air corridors with the rest for the military, a practise that China continues.
Can't say how the US would have responded, depends on the type of facility and the infraction. Most likely a radio warning and a complaint to the airline/government. In more serious cases the aircraft might be intercepted and forced to land but this would difficult if the aircraft returned to international airspace (I'm not sure of the legal position).