NOVA joins an exclusive dive beneath the waters of Pearl Harbor to trace new clues to the historic sinking of the USS Arizona. 1,177 crew members perished in the dramatic 1941 sinking of the storied battleship-the greatest loss of life in United States naval history. For decades, it has been thought that the Arizona was brought down by fire from Japanese aircraft. But the discovery of a Japanese "midget sub" displaced from the scene of the battle raises new questions about the Arizona's final hours. Severed into three pieces and dropped in 1,200-foot deep water outside of the harbor, the sub matches four other experimental vessels discovered in shallower water closer to the harbor entrance. All were equipped with a pair of torpedoes-but only the torpedoes of the fifth sub are still missing, apparently fired at an unknown target. What was the submarine's mission? Why was it laid to rest so far from the harbor? What was the fate of its two-man crew? With unprecedented access to the Arizona wreckage, NOVA teams up with the Hawaii Undersea Research Lab to use manned deep submersibles in an attempt to resurrect the fifth midget submarine.