After Coast Guard captain Jack Matthews, a widower, heroically dies while fighting a ship fire, Chief O'Malley and his wife Nora rear his orphaned son Grad along with their own boy Hap. Several years later the two young men follow in the steps of their fathers and together join the Coast Guard Academy in New London, Connecticut. Later, after O'Malley is transferred to the Academy's training ship, Eagle , he and Nora move to town, and the three men are assigned together when Grad and Hap take their first cruise. During a storm one night, all hands are called to the deck, and Hap and Grad are ordered to climb the mast to adjust the sails. At the top, Grad faints and must be carried down. Later, after overhearing the other cadets joke about him, Grad climbs the mast alone, forcing himself to overcome his fear. Later, on the deck, Grad intimates to O'Malley how he is anxious to live up to his father's heroism, but the proud O'Malley reassures him. Meanwhile, Hap has been dating a young woman, Pat Kirby, and often invites Grad to join them on dates. Although Pat seems taken with Grad, Grad maintains his distance. However, several months later, Grad and Pat run into each other at a waterfront tavern and she frankly admits that she is more interested in Grad than Hap. Although Grad reciprocates her feelings, he knows Hap feels strongly for her. While they are dancing and talking, Hap shows up, and feeling betrayed, breaks off with both of them. When Grad becomes upset that he hurt Hap, Pat construes his conflicted feelings as disloyalty to her, and leaves in anger. Now alone, Grad drinks heavily and crashes his car on the drive home, which gets him expelled from the Academy. Pat tries to apologize, but Grad will not listen, and after quarreling with Hap, he makes impulsive plans to run away, feeling that a career with the Coast Guard is no longer possible. O'Malley stops him and suggests that he enlist, as he can still become an officer by working his way up the ranks as his father did. Following O'Malley's suggestion, Grad starts over as an enlisted man and is assigned to the ice patrol on the Coast Guard cutter, Westland , under Capt. Holland. In a dangerous rescue operation, Grad, now a junior boatswain's mate, and O'Malley, who is also assigned there, pull trapped men out of a downed plane, and the impressed Holland promotes Grad to first class. O'Malley, who is proud of both of his sons, asks Holland to transfer him to New London for the summer so that he can attend Hap's graduation, and asks also that Grad be transferred, as he hopes that the young men will make peace. When Holland approves the transfer, Grad reluctantly agrees to go. However, while O'Malley, Nora and Pat attend Hap's graduation ceremony, Grad is too ashamed to attend and ignores Pat's overtures to reconcile. When the three men are together, Hap snubs Grad, as he thinks Grad blames him for his expulsion, but Grad confides to O'Malley that he does not hold Hap responsible. O'Malley convinces Grad to make up with Pat, and when his two sons are assigned together with him on the ice patrol, he arranges for them to work together. At Christmastime, Nora invites Pat to celebrate with them. Pleased to see Pat, Grad explains that he has ignored her because he was ashamed that he is not an officer and they discuss future plans together. Although Hap is uncomfortable, O'Malley philosophizes that he must work through his feelings, just as Grad had to deal with his expulsion. After the three men return to the Westland , they are confronted with a runaway iceberg, which crashes into a cruise ship and runs it aground on the ice. To break the ice so that the Westland can tow the cruise ship, O'Malley suggests to Holland that charges be set and volunteers himself and his sons for the dangerous job. They set charges on the berg, and then take cover, but the charges do not blow as expected. Hap runs back to check on them and Grad impulsively follows. When the explosion occurs, Hap is injured in an avalanche of fallen ice, but Grad risks his life to pull him to safety. Meanwhile, the cruise ship is pulled free of the berg, and many civilian lives are saved. Later O'Malley, Hap and Grad are decorated for bravery, as Nora and Pat proudly watch. Grad, who is now a chief boatswain's mate, and Pat have plans to marry, and as the rift between Grad and Hap has healed, the O'Malleys are again a united family.