John Wayne and Patricia Neal did not get along during filming. She was particularly annoyed by his treatment of a gay publicity man. Nearly fourteen years later, however, they worked together on In Harm's Way where she noted that he had mellowed a lot, possibly because he was seriously ill with lung cancer at the time.
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.
During filming Gary Cooper visited the set to persuade his mistress Patricia Neal to abort his child. Neal later became a pro-life activist.
The problems with submarine torpedoes shown in the movie are accurate. A poorly designed and tested firing pin could malfunction on a good hit (that is, a torpedo striking within about 45 degrees of perpendicular to the side of the target). Poor hits (at a very sharp angle to the side of the ship) could often produce more reliable explosions. Finding the problem, while not performed by the submarine crews as shown, actually did occur in a similar manner.
This movie's opening foreword and dedication states: "When the Pacific Fleet was destroyed by the Japanese sneak attack on Pearl Harbor, it remained for the submarines to carry the war to the enemy. In the four years that followed, our undersea craft sank six million tons of Japanese shipping including some of the proudest ships of the Imperial Navy. Fifty-two of our submarines and thirty-five hundred officers and men were lost. It is to these men and the entire 'silent service' that this picture is humbly dedicated."