Also The War Game from 1966 by Peter Watkins. Was commissioned by the BBC to prepare the public for a nuclear strike, but was then not televised as "the effect of the film has been judged by the BBC to be too horrifying for the medium of broadcasting". Went on to be considered one of the best British documentaries of all time, and one of the most realistic depictions of the effects of a nuclear strike on a populace.

https://en.wikipedia.org/wiki/The_War_Game

Can be watched here: https://archive.org/details/TheWarGame_201405

Can be watched here: https://archive.org/details/threads_202007

Careful with "Threads" - I've heard from normally stout people that it sent them into a funk because it was rather traumatic.