The American USS ''Haynes'' detects and attacks a German U-boat that is on its way to rendezvous with a German merchant raider in the South Atlantic Ocean. Lieutenant Commander Murrell (Robert Mitchum), a former officer in the merchant marine now an active duty officer in the United States Navy Reserve, has recently taken command of ''Haynes'', even though he is still recovering from injuries incurred in the sinking of his previous ship. Before the U-boat is first spotted, one sailor questions the new captain's fitness and ability. However, as the battle begins, Murrell shows himself to be a match for wily U-boat ''Kapitän-Leutnant'' von Stolberg (Curd Jürgens), a man who is not enamored with the Nazi regime, in a prolonged and deadly battle of wits that tests both men and their crews. Each man grows to respect his opponent.