The War Story – 1965 BBC documentary about nuclear war (medium.com)

There is a copy with the full film here (it's about 50 minutes long)

https://vimeo.com/90896890

My high school chemistry teacher showed us this film in class. This was c. 1980, so early Reagan cold war era. It didn't seem that far away. The pseudo-documentary presentation didn't pull any punches, unlike Hollywood type treatments.