I first owned this as a Betamax tape. I later bought it on VHS and much later still on DVD.
I think I first saw it on TV, probably in the 50s or 60s (I wan't born when it was first released) and many times since. A brilliant cast, mainly of established British actors many of whom were then in full active service in reality - John Mills and John Laurie certainly were!
Although it does a very good job, and was made under tight wartime budgetary constraints, as would be expected as WWII was then just beginning to turn in favour of the Allies, it does not come close to matching the atmosphere, or showing the effects upon the crews, of the later German-made 'Das Boot' - probably the best and most authentic submarine movie (although made originally as a TV series) ever made - it is the best British equivalent.
'Above Us the Waves' is another excellent British submarine movie, but concerning the so-called midget submarines that were used against the battleship 'Tirpitz'. It isn't completely comparable as the vessels were very much smaller and with a much reduced crew, but it does have its own unique atmosphere. The midget submarines used in the movie may not have been those used in the actual attack but were very similar.
Many of the US movies in this genre were either outright comedies, 'Operation Petticoat' for example, or the "We Won The War" flag-waving variety such as 'Torpedo Run', both of which are perfectly enjoyable in their respective ways but not especially authentic. I cannot think of an American movie to directly compare with either of the British titles.