'The Undersea Warship') is a 1963 Japanese tokusatsu science fiction film directed by Ishirō Honda, with special effects by Eiji Tsuburaya.

The film stars Jun Tazaki, Tadao Takashima, Yōko Fujiyama, Yū Fujiki, and Ken Uehara.

Her father's former superior, retired Rear Admiral Kusumi is confronted by a peculiar reporter, who claims contrarily that Captain Jinguji is alive and at work on a new submarine project.

The threads meet when a mysterious taxi driver attempts to abduct Makoto and the Admiral, claiming to be an agent of the drowned Mu Empire.

Contained within is a film depicting the thriving undersea continent (with its own geothermal "sun") and demanding that the surface world capitulate, and prevent Jinguji from completing his Atragon submarine, named Gotengo.

After several days of travel, the party find themselves on a tropical island inhabited only by Jinguji's forces and enclosing a vast underground dock.

He built Gotengo, he explains, as a means to restore the Empire of Japan after its defeat in World War II, and insists that it be used for no other purpose.

Gotengo's test run is a success, the heavily armored submarine even elevating out of the water and flying about the island.

After Makoto and Susumu are kidnapped by the reporter, and the base crippled by a bomb, Jinguji consents to Kusumi's request and prepares Gotengo for war against Mu.

The Mu Empire executes a devastating attack on Tokyo and threatens to sacrifice its prisoners to the monstrous deity Manda if the Atragon appears.

The Captain then advances Gotengo into the heart of the Empire power room and freezes its geothermal machinery before successfully escaping to the surface.

Sekizawa thought up the character of Jinguji after reading about the Brazilian-Japanese groups Machigumi and Kachigumi, one of which felt that Japan should have won World War II.

There is some debate as to whether Manda was always in the script (a snake monster doesn’t appear in the Undersea Kingdom) or whether the beast was added at Tomoyuki Tanaka’s insistence like he did with Maguma in Gorath (1962).

However, no one approached the actor prior and by the time casting was underway Mifune was already tied up in rehearsals for what would be a 18 month shoot for Red Beard (1965).

Ishiro Honda had no idea whom to cast as the Empress of Mu but met Tetsuko Kobayashi by chance, who was working on a TV show in Toho's lot.

This version was fully operational with wings, fins, gun turrets, the bridge, and the drill all movable by remote radio control devices built into the hull.

The final cut of the scene utilized a one-meter model to depict the Gotengo slowly flying forward in a long shot.

The royal contingent, consisting mostly of the wives of American servicemen, was placed on a small platform with the pillars, balcony, and antechambers all painted in perspective on the backdrop.

The chamber was filled with 600 male and female dancers who were choreographed by Ishiro Honda to Akira Ifukube’s Mu ritual music.

Natural sunlight was sufficiently bright for filming only between 3:00PM and 4:00PM, so preparations were made from sunrise to ready the set for a tight afternoon shooting schedule.

The mu submarines which were destroyed by the Gotengo’s freeze cannon were 2 cm models built to float upside down in the water tank.

The scene where Shingugi’s strike team uses freeze ray guns on attacking Mu soldiers was done using matte paintings.

[6] American International Pictures afforded the film a successful US theatrical release in 1965, with minimal changes and quality dubbing by Titra Studios,[7] as a double feature with The Time Travelers.

This shortening from four to three syllables was the choice of AIP, since several European markets released the film as Atoragon (Italy) and Ataragon (France).