In August 1943, the U.S. Navy submarine USS "Tiger Shark" patrols the Atlantic Ocean during World War II. Receiving orders to pick up survivors spotted adrift by a British PBY Catalina patrol plane, the submarine rescues three survivors – British nurse Claire Paige (Olivia Williams), and two men, one of them wounded – from British hospital ship "Fort James", sunk two days earlier; one survivor blames a German U-boat he spotted on the surface just before "Fort James" suffered a torpedo hit. The "Tiger Shark" crew spots a German destroyer approaching. The submarine has several encounters with the destroyer and suffers damage from depth charges. Commanding officer Lieutenant Brice (Bruce Greenwood) discovers the wounded survivor is actually a German prisoner-of-war, Bernhard Schillings (Jonathan Hartman). Believing Schillings has been making noise to betray "Tiger Shark"s position to the German warship, Brice confronts him, shooting Schillings dead when the German panics and grabs a scalpel to defend himself.