''Atragon'' (aka ''Kaitei Gunkan'', or ''Undersea Warship'') is a 1963 tokusatsu film from the producers and crew of ''Franchise/{{Godzilla}}''.

The lost kingdom of Mu, which sank beneath the sea over twelve thousand years ago, launches an assault to make the upper world their domain again. With an array of weaponry, the Mu Kingdom wages a war with the surface dwellers, who counter with the super-scientific battleship Gotengo.

As the Gotengo attempts to defeat the Mu Kingdom in their own underwater base, the Mu unleash the legendary sea dragon Manda against the humans.

This movie introduces Manda to the Creator/{{Toho}} universe, who was later incorporated into the Godzilla universe. It also marks the first appearance of the Gotengo, which became one of Toho's signature military battle vehicles. Gotengo appears 2004's ''Film/GodzillaFinalWars'', which recreates the battle between the Gotengo and Manda from this film.

See also ''Anime/SuperAtragon''.
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!!Tropes that apply to ''Atragon'' include:

* CallingTheOldManOut: Captain Jinguji is so fixated in restoring Japan's honor after the nation's defeat in World War II that everyone, including his own daughter, calls him out on this. Granted that Nationalism and Patriotism is the basic themes of this film, but he actually took it too far.
* CoolShip:
** The Gotengo.
** Subverted with the Red Satan, supposed to be a super-advanced submarine but is destroyed after one encounter when is pursues a Mu submarine past crush depth.
* DoomsdayDevice: Mu's seismic generator.
* DidYouJustPunchOutCthulhu: The Atragon froze Manda to death.
* DubNameChange: Gotengo to Atragon.
* TheDragon: Manda literally is one, but he's a guardian monster
* GenreBusting: Toho's war films were very popular during the 1960s, so writer Sekizawa came up with the idea of combining Toho's popular war films with their fantasy/kaiju films and voila...
* IntrepidReporter: Played with. Umino seems to take his job seriously in an odd matter. Later defied when he was [[TheMole a Mu Agent all along]].
* NoNameGiven: The Mu Agents and the Empress. As well as her Chancellor.
* PapaWolf: It took Captain Jinuji a long ass time to see he should use the Atragon to save his daughter. And he ''does''.
* PlayingAgainstType: Akihiko Hirata plays as TheDragon, Mu agent 23. He plays another Dragon later in ''Film/EbirahHorrorOfTheDeep'' with [[ActorAllusion an eyepatch]].
* SceneryPorn: The panoramic shots of the kingdom of Mu are breathtaking. Tsuburaya-sama outdid himself on this film.
* TheStoic: Captain Jinguji, played by the master of stoics, Jun Tazaki.
* YamatoNadeshiko: The Empress of Mu.
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