In 1918 during World War I, the United States Navy submarine ''AL-14'' is sent with the rest of Submarine Flotilla 1 to Taranto to fight in the Adriatic Sea. The submarine's commander was wounded on its last cruise, and Lieutenant Thomas Knowlton (Robert Montgomery (actor)), his second in command, expects to be promoted and take his place. However, Lieutenant Commander T. J. Toler (Walter Huston) shows up and takes over.