Robert Mitchum stars as Captain Murrell, commander of an American naval destroyer USS Haynes in the South Atlantic during WWII. Murrell was a civilian sailor, a merchant mariner who saw his new wife die when a German U-boat torpedoed his freighter. Now he is in the US Navy attempting to do his bit to win the war. The Haynes comes across an unexpected sonar signal and follows it to discover a German U-boat returning to its base. The U-boat is under the command of Von Stolberg (Curt Jurgens), a competent and experienced officer who has become increasingly disillusioned with the aims of the German government in this war.
The Haynes pursues the U-boat, but when the U-boat's captain takes action the battle escalates, with both men needing to use all their skills and experience in an attempt to gain the upper hand. Murrell's aim is to delay the U-boat long enough for additional support to arrive, while Stolberg is trying to reach the German fleet in order to deliver a stolen Allied codebook. These two capable officers and their crews find themselves locked in a deadly game of cat and mouse, knowing that only one is likely to survive.
This classic WWII adventure doesn't fall into the trap of many of its contemporaries and avoids indulging in flag-waving or German-bashing, even if it has to make clear that Stolberg doesn't like his government in order to achieve this. Instead, both captains are portrayed as equals – competent, honourable and human – a rarity in films from this period. The tension is relentless, building to a most satisfactory climax, and the film continues to entertain in spite of its age. Some of the sea battles are clearly done with models, and also borrows from existing newsreel footage, but in general the film is very competently made within the technical limitations of its time.