In late 1941, Joel Kennedy, the longtime managing director of the Point Pleasant drydock and shipbuilding company in California, is distraught to learn that the Maritime Commission has given a contract to Matt Braddock. Matt, who has successfully built bridges, roads, buildings and other structures, has never worked in a shipyard before, but believes that by using prefabricated pieces and welding them instead of using rivets, the yard can quickly manufacture structurally sound ships. Kennedy's daughter Diana and his right-hand man, Jim Benson, are also opposed to Matt's seemingly radical ideas, but his son Russell, a high school student, is thrilled by the new technology and is eager to learn from Matt. When Matt arrives with his assistant, Johnny Rogers, everyone in the town gives him the cold shoulder, and he is upset to learn that only one worker has been assigned to fill in the swamp land he has designated to be used for new shipways. Matt's insistence on putting all the workers onto the shipways project further alienates Kennedy, who quits, but when Russ impresses on his father how much their country needs them, Kennedy has Jim instruct the reluctant workers to follow Matt's orders. Matt faces another obstacle, however, when the city council refuses to provide housing for the additional thousand workers that he has employed. The workers eventually wind up in a trailer camp, and when the townsfolk learn of the attack on Pearl Harbor, everyone forgets their differences and pitches in to build Matt's prefab ships. Kennedy and Jim are still skeptical of Matt's plan to assemble a ship's superstructure separately and then lift the 180-ton structure onto the ship's hull, but Matt insists that it can be done in time to meet the deadline for their first ship. One night, Jim sees Diana, to whom he is engaged, share a passionate kiss with Matt, and is so angry that he does not review a crucial welding plan for the superstructure. As a result of Jim's oversight, of which Matt is unaware, the superstructure collapses as it is being lifted onto the hull and Russ is crushed by the falling debris. In the hospital, the dying Russ encourages Matt to continue with his work, but Matt, overcome by grief and believing himself to be responsible for Russ's death, plans to leave town and asks Kennedy to reassume control of the shipyard. When Jim overhears Matt and Kennedy's discussion, however, he realizes that he was responsible for the welding error and confesses his mistake to Kennedy. Now realizing that Matt's plan is feasible, Kennedy and Jim organize the workers and quickly assemble another superstructure. Diana meets Matt at the train station as he is about to leave and persuades him to return to the shipyard with her. There, they witness the successful launch of the first ship, which Mrs. Kennedy christens the Russell Kennedy . Later, Matt has received orders to start prefabricated shipyards throughout the country, and Diana, with whom he is in love, agrees to accompany him on his patriotic mission.