A superb cast in a superb story; the best performance ever by the amazing Jack Hawkins.
Powerful, emotional, yet low-key and convincing. If only other war dramas which try for this level of achievement-like say "Das Boot", which seems to get three extra stars for having subtitles- could emulate the quality of this. The scene where Hawkins sends his ship through British survivors to try to get the U boat is simply one of the best in any war film ever, frankly in any film of any genre.
Ten stars would hardly be too many. Unusually, this does full credit to the book.