USS ''Tiger Shark'' is a U.S. Navy submarine on patrol in the Atlantic Ocean during World War II in August 1943. She receives orders to pick up survivors spotted adrift by a British Consolidated PBY Catalina patrol plane. She retrieves three survivors – the British nurse Claire Paige (Olivia Williams) and two men, one of them wounded – from the British hospital ship ''Fort James'', which had been sunk two days earlier; one of the survivors blames the sinking on a German U-boat that he briefly saw on the surface just before ''Fort James'' suffered a torpedo hit. As they pick up the survivors, the crew of ''Tiger Shark'' spots a German destroyer bearing down on them. The submarine has several encounters with the German destroyer and suffers damage from depth charges in the process. Later, the commanding officer of ''Tiger Shark'', Lieutenant Brice (Bruce Greenwood), discovers that the wounded survivor is actually a German prisoner-of-war, Bernhard Schillings (Jonathan Hartman). Brice confronts him because he thinks Schillings has been making noises to betray ''Tiger Shark''s position to the German warship. Brice shoots Schillings dead when the German panics and grabs a scalpel to defend himself.