Gotta admit I am a sucker for these (Submarine/U-Boat) type of films. This one, Das Boot, The Hunt for Red October, Crimson Tide, U571, Run Silent Run Deep are all films I have seen and enjoyed. I am wondering if there are any others that I may be missing out on. And yeah Das Boot is the King.
The running gag in Crimson Tide is the ongoing submarine movie trivia quiz. One of the correct answers is "The Enemy Below." I'm not sure, but I think the question is, "Stars Robert Mitchum and Curd Jurgens."
Hell and High Water (1954) Destination Tokyo (1943) Down Periscope (1996) -comedy but good. Enigma (2001) Torpedo Run (1958) Submarine Command (1951) Phantom (2013) - kinda weak worth one watch K-19 (2001) - also kinda weak but worth one watch as well In Enemy Hands (2004) - takes place on a sub, not really a sub movie per-say, more of a POW story, William H Macy & Scott Caan both star.
Blue Submarine No. 6 - Anime future sci-fi fantasy, but quite good(ranked as the 70th best anime of all time by the Japanese magazine Animage, 25th best anime of all time by Wizard's Anime Invasion, & "Best OVA, U.S. Release" for 2000). I'm not a big anime fan, FTR.
Full Fathom Five (1990) & USS Seaviper (2012) - So bad they're kinda fun to watch
Up Periscope (1959) drama starring James Garner Run Silent Run Deep (1958) Clark Gable plays the radar antenna Operation Pacific (1951) Operation Petticoat (1959)
Captain Horatio Hornblower RN is another great naval warfare movie, although it doesn't involve subs (since it takes place during the Napoleonic wars in the early 19th century).
All the other sub movies I know of have been listed already.