After the death of a commander during World War II, a lieutenant takes charge of a team of demolition divers known as frogmen; the British navy fights desperately to destroy the Nazi battleship Bismarck; a German soldier becomes a spy for the British during World War II and is planted aboard a German freighter; commanders of an American destroyer and a German U-boat play a deadly game of cat and mouse.ng World War II and is planted aboard a German freighter; commanders of an American destroyer and a German U-boat play a deadly game of cat and mouse.