On patrol in the Pacific during World War II, the U.S.S. Seahawk submarine, under the command of Lt. Comm. Dean Stoker, prepares to rendezvous with a supply ship but receives an urgent command to return Pearl Harbor, Hawaii instead. Stoker summons Lt. Paul Turner, a taciturn, solitary officer, to advise him that he is turning in a negative report on him, for although he is an excellent tactician, Turner has no interest in building rapport with the men with whom he serves. Upon arriving in port, Stoker assures his executive officer, Bill Hallohan, that he will certainly receive his own command, and both wonder about Turner’s fate. Stoker meets with Capt. Boardman who reveals that the Seahawk is to return to sea immediately with a mission to locate over thirty missing Japanese warships. Stoker is startled when Boardman indicates that much of the intelligence for the mission was provided by Turner who also speculated that the Japanese may be forming a reserve force. When Boardman reveals that Stoker is being pulled from sea duty to assist in coordinating a counter-attack force, the commander is furious, but ultimately accepts his promotion, hoping that the selection committee will give the Seahawk to Hallohan. The committee appoints Turner, however, because of his vast knowledge of Japanese ships, angering Stoker and disappointing Hallohan, who is to remain the Sea Hawk ’s executive officer. Turner bids farewell to his wife Ellen as Seahawk sailors are pulled from shore leave to return to duty. Turner meets with Hallohan and Lt. David Shore, a young officer on his first mission, to read their orders which stipulate the mission is strictly one of reconnaissance. Turner considers it best the crew not be informed about the true nature of their mission, in order to keep them primed for action. Very soon, however, after the Seahawk determinedly avoids engaging with enemy ships, the crew begins to suspect their new captain of cowardice. Chief Andy Flowers struggles to maintain discipline, but when the crew performs sloppily, Turner orders more drills, further alienating the sailors. Later, Turner confides in Hallohan his suspicion that Shore may be unstable and the exec concurs that the behavior of the young officer has been erratic. One day while patrolling on the surface, the submarine is strafed by a Japanese scout plane which damages the radio antennae and kills a sailor. Hallohan is surprised that Turner is affected by the first death under his command, but disagrees sharply when the captain orders them to surface to make immediate repairs on the antennae. The Seahawk is spotted by an American cruiser who, receiving no signal, believes it to be an enemy vessel and attempts to ram it. Forced to the bottom of the sea, the Seahawk then endures numerous depth charge explosions, shaking the crew’s confidence badly. After communications are restored, Turner contacts Boardman who approves his request to continue the next phase of what has been named Operation Forager. Over the next few days, Turner orders the Seahawk further into the Pacific in search of the missing Japanese ships. Upon encountering an enemy tanker, destroyer and escort, Turner finally engages, only to miss each ship and have his submarine pummeled by depth charges. Shore, who has grown increasingly anxious, asks Hallohan if he believes Turner is afraid and suggests the exec office should relieve the captain. Turner consults with Hallohan and reveals he believes the tanker was in the area to refuel ships. Plotting the speed and direction of the enemy ships, Turner concludes that the Japanese may be using one of three nearby islands to dock their reserve fleet. Hallohan reminds the commander that American air forces decimated the islands and several enemy ships some months back, but Turner believes that is the reason the Japanese are using the area. Upon spotting a carrier at a distance, Turner orders the sub to follow, heightening Shore’s anxiety. As the Seahawk closes the gap with the carrier, Turner realizes it is entering a mined harbor and plans to follow directly in its wake. Overcome by panic and tension, Shore, while alone on the command deck, starts issuing orders to attack the carrier. Hallohan attempts to intervene but Shore knocks him out. Turner ultimately talks Shore into surrendering and he is placed under arrest and sedated. Once in the harbor, the Seahawk spends the night on the ocean floor. At dawn, the sub surfaces to periscope depth where Turner and Hallohan confirm an entire task force is anchored in the island harbor. Knowing they risk detection, Turner nevertheless sends a coded message to Boardman giving the harbor’s coordinates. Turner then informs the crew of their true mission and the risk they face. In a few hours, a tremendous American air attack begins as the Seahawk waits at the bottom of the sea. When several Japanese ships break apart under the bombardment, the submarine is struck by falling debris. Learning that some men have died and several sailors are trapped by wreckage that has broken through the hull, Turner orders the submarine to blow its tanks and surface. The move is successful and the debris is safely dislodged. The Seahawk rises to find a surviving carrier attempting to flee and Turner orders an attack which sinks the ship. Proud of the captain, their ship and their mission, the crew happily set sail for their return to Pearl Harbor.