Richard Houston, a former Naval officer who deserted because of gambling debts, rejoins the U.S. Navy under a fictitious name, after the Japanese attack Pear Harbor. He makes friends with Chief Petty Officer "Fixit" Smith, who takes him home where Houston meets Smith's niece, Mary. Houston, with his prior service, makes quick progress and is soon promoted to Gunner's Mate, along with Seaman Elliott Nash, his chief rival for Mary. During a diving operation, Nash saves Houston's life but Lieutenant Ralph Gilpin discovers a watch in Houston's pockets inscribed to Richard Houston, and starts an investigation into his real identity. Houston, to win money for an engagement ring for Mary, gambles and overstays his shore-leave, and his friend Smith takes his place and is killed when the Minesweeper strikes a Jap mine. Houston discloses his true identity to Mary and plans to desert again. But after hearing an emergency broadcast for all Navy men to report to their base, he returns and is placed on a minesweeper with Nash to locate a new type of Japanese mine in the harbor.