Beneath the surface of Pearl Harbor lies Japan's ultimate killing machine. 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 where more than 1,000 crew members perished in the greatest loss of life in United States naval history. For decades, it has been thought that a bomb dropped by a Japanese aircraft sank the Arizona. But the discovery of a group of Japanese midget subs in and around Pearl Harbor has raised questions about the battleship's final hours. In this programme, Nova's team of expert investigators journeys to the seafloor to explore the wreckage of the most mysterious of these subs. Did this mini-sub and its two-person crew make it into Pearl Harbor and fire torpedoes at the Arizona? Nova pursues this puzzle with unprecedented access to the remains of the Arizona and other unique evidence, including aerial photos taken by Japanese aircraft and moving testimonials from U.S. and Japanese veterans. "Killer Subs in Pearl Harbor" is a gripping investigation into 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.