Trivia

The movie was filmed on a low budget. As a result most of the shots of the submarines, ships and the scenes were either taken from other films or stock footage from World War II.

John Wayne was dissatisfied with the finished film, believing it to be overlong and containing too much romance. He was also opposed from the beginning to the casting of Patricia Neal, whom he felt was too young at 24 for the role of his ex-wife. By the time of their next film together ( In Harm's Way (1965) ) he felt that she had matured as an actress and the two got along very well.

During filming Gary Cooper visited the set to persuade his mistress Patricia Neal to abort their unborn baby. Neal acquiesced to his demands and later expressed overwhelming regret at not giving birth. She became an anti-abortion activist in later years, and converted to Catholicism shortly before her death from lung cancer in 2010. Cooper punched Neal in the face after he saw Kirk Douglas attempt to seduce her, the only time he is known to have hit a woman.

The problem with the torpedoes depicted in the movie was actually one of several problems the USN experienced with its torpedoes. In addition to the firing pins their magnetic detonators were unreliable as was the torpedo's ability to maintain correct depth. The torpedo was designed to either strike the target directly or pass under the target and detonate under the keel thus breaking the ship's back. If the torpedo ran too shallow it struck the target, and given the firing pin defect, may not detonate. If the torpedo ran too deep the magnetic trigger could not detect the ships magnetic field thus passing under the ship without detonating. The torpedoes were so unreliable that multiple torpedoes were fired at each target in a "spread" such that the ship's stern, bow, and midships were each targeted in the hope that one would find its target AND detonate. Returning from a patrol having fired all 24 torpedoes resulting in 3 or 4 enemy ships sunk was considered a very good patrol, one to be proud of and even brag about. The USN Bureau of Ordnance (BuOrd) was responsible for the development and testing of USN torpedoes. Even though the defects were obvious to everyone who fired the weapon in combat, BuOrd's insistence that the torpedoes were without defect bordered on the criminal. Their pigheadedness resulted in delaying the deployment of reliable torpedoes by at least two years.

The rescue of the women and children is based upon an incident involving the USS Crevalle. The sub took 40 refugees off Negros Island in the Philippines including women, children and some survivors of the Bataan Death March. The rescue was just a cover story. The real reason the sub was sent there was to retrieve a group of important documents, namely the Japanese "Z plan", found by the local guerrilla unit from the crash of a plane carrying the chief of staff of the Japanese Combined Fleet.