Atragon (海底軍艦, Kaitei Gunkan, lit. The Undersea Warship) is a 1963 Japanese science fiction film produced and distributed by Toho. It is based on The Undersea Warship by Shunrō Oshikawa and The Undersea Kingdom by Shigeru Komatsuzaki. The film is directed by Ishirō Honda, with special effects by Eiji Tsuburaya and stars Jun Tazaki, Tadao Takashima, Yōko Fujiyama, Yū Fujiki, and Ken Uehara.
The film was released in Japan on December 22, 1963, and in the United States in 1965 via American International Pictures. A two-episode OVA titled Super Atragon, based on the same novels, was produced by Phoenix Entertainment in 1995.