1962 - Cuban Missile Crisis - has it lasted another week.
1973 - Mid-East war, when Moscow threatened to back Egypt against Israel.
(most folks don’t know this was much more serious than 1962, as U.S. had nukes on highest alert ever.)
In ‘62 and ‘73 we had a civil defense program, plus CONELRAD radio alerts.
Neither of your events developed into an emergency, though.
Look up teh old propaganda film “Our Cities Must Fight”, this is still our stance. Keep the populace in the dark until the last minute, then tell them to shelter in place. The goal is to get emergency gear out of target cities, and they want the streets clear to do this. If nukes were launched, you’d hear about it 10 mins before impact, so they can get cops and fire trucks and medical supplies out.