In the South Pacific, submarine officer Duke Gifford (John Wayne) and the crew of the “Thunderfish” are attacked by the Japanese during a rescue mission, and their torpedoes malfunction. Returning safely to Pearl Harbor, Duke meets his ex-wife, Mary (Patricia Neal), who still feels strongly for him but is engaged to a pilot, the brother of Duke’s commander, Pop Perry (Ward Bond). Determined to win Mary back, Duke is sidetracked when he and the crew are ordered on a mission with new torpedoes.