Overblown and overrated

This "subsploitation" movie (or "submarine exploitation" as a war movie sub-genre) has aged badly. It's way too long, to start with.

Second, there have been many better renditions of submarines either at a time that was closer to the war (1940s, 1950s and 1960s movies) or more recent movies.

Why does all the crew look dirty from the start? The Navies, all over the world, have strict codes. Scraggly beards and long hair, tolerated in the German navy? I don't think so. Facial hair is tolerated in the Navy all over the world, sometimes only for officers, under the condition that it's kept clean and trimmed. Hair is still supposed to be short, even more so in Nazi Germany. Lack of hygiene and cleanliness, especially under tough circumstances, was considered as lack of discipline.

The film suffers from the start from the fact that it's hard to side for 1940s German U-boats (whose job it was to sink anything, including civilian vessels, in the Channel) and feel sympathetic to them (how do you think you got advancement and were given the rank to command a ship under the third Reich?)... Starting from that, the movie should really try to make us like the characters, but it really fails.
I don't understand the high ratings at all. There are a lot of other movies, including depicting the "enemy side" that are better and more gripping.