Rival ship captains join the Navy and fight German submarines.
In 1918 German submarines sank more than eighty American ships. John Thorson (Wallace Beery) tells his daughter Susan Thorson (Virginia Grey) that Rocky Blake (Chester Morris) sunk their ship to get the contract. Spanish War veteran Cap Finch (Clem Bevans) tries to recruit Thorson for the Navy. Susan urges her father to get the contract, and she puts on a dress for Rocky. They argue, but she gets Rocky to talk with her father, who calls Rocky yellow. Thorson goes to enlist; Rocky signs up first, but Thorson does not. Susan and Thorson see a submarine, and Germans board them. Thorson fights the U-Boat Captain (Carl Esmond) and is knocked out. Their crew gets in a boat, and Susan and Thorson in another before their ship is blown up. Thorson signs up and is made an ensign of a ship under Rocky, who expects discipline. Susan gives Rocky coffee and asks him to help her father, and she makes her father promise to obey Rocky.
Thorson leaves the stormy area and hears a sub. Thorson fires depth charges and hits it; but they see a ship sunk by a torpedo. Thorson goes in to free propellers with a hacksaw. Rocky dives in to rescue Thorson. The District Commander (Douglass Dumbrille) tells Rocky that Thorson should not have left the squadron. Rocky says Thorson may die. Susan cries on Rocky's shoulder. Thorson recovers, but Rocky announces he was found guilty and is demoted ashore. Rocky tells crying Susan that her father must obey orders. Thorson paints a ship.
Germans destroy ships. Admiral Girard (Jonathan Hale) and the District Commander order Rocky to send out a mystery ship. Thorson reports to the schooner and has to clean bilge but quits. He tells Susan he is going to sea; she refuses to go against the Navy but changes her mind and joins him. Rocky catches them getting in a boat. Rocky sends Susan home and takes Thorson on a fishing boat. Thorson sees a sub, and Rocky radios. Thorson identifies the U-Boat Captain. Germans come on board and find Navy equipment. They fight, and their ship is sunk. Thorson is captured as the squadron approaches and fires depth charges. Rocky and his men are rescued. They stop to listen. In the German sub Thorson escapes to make noise. Rocky orders attack in spite of Thorson. Suffering from gas, the Germans surface and surrender. Thorson saves the German captain as the sub sinks. In the final scene District Commander gives Thorson the medal of honor, and Rocky tells Susan they are going to France.
This world war drama prepares Americans for the probability
that they will soon be fighting Germans again, and the emergency
enables the quarreling rivals to gain a spirit of cooperation.