Atragon

Atragon, released in Japan as Undersea Warship , Kaitei Gunkan? , is a 1963 science fiction tokusatsu film directed by Ishir Honda and produced and financed by Toho. It is based on a series of juvenile adventure novels under the banner Kaitei Gunkan by Shunr Oshikawa heavily influenced by Jules Verne and the illustrated story Kaitei Okoku The Undersea Kingdom by illustrator Shigeru Komatsuzaki, serialized in a monthly magazine for boys. Komatsuzaki also served as an uncredited visual designer, as he had on The Mysterians 1957 and Battle in Outer Space 1959. visualizing the titular super weapon, among others.

The legendary empire of the lost continent of Mu reappears to threaten the world with domination. While countries unite to resist, an isolated World War II Captain has created the greatest warship ever seen, and possibly the surface worlds only defense.While on a magazine photo shoot one night, photographers Susumu Takashima and Yoshito Yu Fujiki witness a car drive into the ocean. While speaking with a detective Hiroshi Koizumi the next day they spot Makoto Jinguji Fujiyama, daughter of deceased Imperial Captain Jinguji, who is also being followed by a suspicious character Yoshifumi Tajima. Her fathers former superior, retired Rear Admiral Kusumi Ken Uehara, is confronted by a peculiar reporter Kenji Sahara who claims contrarily that Captain Jinguji is alive and at work on a new submarine project. The threads meet when a mysterious taxi driver Akihiko Hirata almost abducts Makoto and the Admiral, claiming to be an agent of the drowned Mu Empire. Foiled by the ensuing photographers, he flees into the ocean. ........

Source: Wikipedia