I'm not sure of the history of submarine films, but I'm willing to bet this was one of the first truly iconic members of the subgenre. The main thing about this film that really caught me by surprise were the excellent action scenes thanks to great model work. There were underwater environments with full models of planes, ships, and of course submarines. In addition, the realistic actions of the crew members makes this feel like almost a documentary of life for submarine crews. This was probably one of the main intentions of the film anyway. The general story is a bit outlandish but also filled with tension, and the characters are exactly what you'd expect from an American propaganda film. The fact that there weren't more inter-crew tensions actually drags the movie down, and the completely nameless and mostly faceless villains also makes the action feel a little odd. Still, an incredibly influential piece of war film.