During the Battle of the Atlantic, after sinking a merchant ship from an Allied convoy, German U-boat ''U-571'' has her engines badly damaged by depth charges from a British destroyer. ''U-571's'' skipper ''Kapitänleutnant'' Gunther Wassner makes a distress call that is intercepted by American intelligence. The US Navy has its submarine ''S-33'' modified to resemble a German resupply U-boat, to try to steal the Enigma machine coding device and sink the ''U-571''. Before the crew of ''S-33'' receives its assignment, the submarine's executive officer Lieutenant Tyler is unhappy about a recommendation for command of his own submarine being blocked by his commanding officer, Lieutenant Commander Dahlgren.