Apologies if I have already listed this before but this is a link to a Navy documentary film from 1957 called "The Navy Frogmen . This is the highest resolution copy I have seen and is missing the "periscope,com" subtitles you usually have to view. Triple tanks. and Churchill fins. Worth watching in the higher res. Note, you can use the gear-like icon at the bottom to enter settings and turn up resolution to 1080P.
https://www.youtube.com/watch?v=syM2zMrTMNo
Here is a link to the Hollywood movie "the frogmen"; No idea if this Hollywood movie entered public domain but it happens to be on youtube.
https://www.youtube.com/watch?v=XDUSZKFwvI4