Submarine films are a subgenre of war film in which the majority of the plot revolves around a submarine below the ocean's surface. Films of this subgenre typically focus on a small but determined crew of submariners battling against enemy submarines or submarine-hunter ships, or against other problems ranging from disputes amongst the crew, threats of mutiny, life-threatening mechanical breakdowns or the daily difficulties of living on a submarine.
The danger from the extreme pressure of deep water dives and the claustrophobic, cramped submarine quarters imbues films of the subgenre with a great deal of dramatic tension. To heighten this tension, these films often depict submarine commanders descending below "hull crush depth" to evade attackers. Films from this subgenre tend to feature dramatic scenes in which submarine-hunters try to destroy submarines with depth charges. A stock scene in the submarine genre film is the depiction of a grim-faced submarine crew waiting in silence as depth charges explode overhead and bolts fly out of bulkheads in the submarine (they are dead silent because sound carries extremely well underwater, and so even the sound of men talking on a submarine would be picked up by normal sonar on other ships). Modern (post-World War II) movies often add conflict between different enemy submarines, something that would have been next to impossible with the limited sensor equipment of earlier times.