Dedicated Navy man Duke Gifford (John Wayne) has a tough time trying to take command of a US submarine following the death of his commanding officer. For one thing, Duke feels guilty over the events that led to the captain's death. Add the fact that his ex-wife (Patricia Neil) is aboard serving as a nurse, and that she's more than determined to become his love interest, and he's a man with a lot on his mind. These factors, plus faulty weapons and a sea full of Japanese ships make his assignment all the more hazardous.