NOVA dives beneath the waters of Pearl Harbor to trace provocative new clues to one of the most tragic events of World War II-the sinking of the USS Arizona. More than one thousand crewmembers perished in the greatest single loss of life in United States naval history. For decades it has been thought that the Arizona was sunk by a bomb dropped by a Japanese aircraft. But the discovery of a group of Japanese midget subs in and around Pearl Harbor has raised questions about the Arizona's final hours. A number of expeditions have recovered evidence of four of the subs pinpointing their final positions and torpedo targets. But when NOVA's team of expert investigators takes a ride to the sea floor in a submersible and discovers the wreckage of a fifth sub they see something intriguing: it's torpedo tubes are empty and it's intended target is at first unknown. So did this fifth sub make it into Pearl Harbor and fire it's torpedoes at the Arizona? NOVA pursues a trail of clues with unprecedented access to the wreck of the Arizona and other unique evidence never seen before including moving testimonials from U.S. and Japanese navy survivors. Killer Subs in Pearl Harbor is a gripping investigation of the possibility that these tiny but lethal mini-subs may have played a crucial and previously unsuspected part in the tragic events of that 'Day of Infamy.'