The ancient race of the undersea kingdom of Mu declares war on the human race to reclaim the surface world as their own. It is now up to the crew of the super submarine Atragon, plus a photographer (Tadao Takashima) and an ex-Japanese Naval Officer (Jun Tazaki), to save mankind. Features an excellent display of miniatures and pyrotechnics directed by special effects master Eiji Tsuburaya and his team. This film introduces another monster that would wind up in the Gojira series, Manda, a giant sea serpent. Manda would later end up co-starring with the rest of Toho's monsters in the Kaiju classic Destroy All Monsters (1968). Also stars Yoko Fujiyama and Kenji Sahara. Also with Ken Uehara, Hiroshi Koizumi, Akihiko Hirata, Eisei Amamoto and Tetsuko Kobayashi.
It was reportedly director Ishiro Honda and special effects director Eiji Tsuburaya who decided to give Manda a dragon-like appearance, because 1964 was to be the upcoming year of the dragon.
This film was released in Japan on December 22nd, 1963, but was not released in the US until March 11th, 1965.
NOTE: This is the very rare AIP English language version of this film, which features a much superior audio dub than all other English language releases.