It is conventional wisdom that there are no bad movies about Submarines. I think I have seen most of them and found this to be largely true. We could easily talk about what was the best Submarine movie (Das Boot, Hunt for Red October, Run Silent, Run Deep, etc...) But out of all the good movies, which was the worst, the least of the best as it were.
My vote goes to Ice Station Zebra, a so-so cold war movie with some good Sub parts but a weak and poorly executed climax. (with deference to Howard Hughes)