THE MYSTERIANS was about a big battle with aliens that takes place on Earth, BATTLE IN OUTER SPACE was about a big battle with aliens in outer space. So I suppose following that logic, it was inevitable that Toho would follow up those films with one that takes place beneath the sea.
This time Earth is threatened by inhabitants from beneath the sea who are descendants of the lost continent of Mu. Much of what is "known" about Mu comes from the speculative works of William Churchwald. Mu is said to be a lost continent like Atlantis, except Mu was in the Pacific. Like Atlantis, Mu was according to Churchwald at least, the home of an advance race that perished eons ago beneath the waves when world wide disaster struck.
ATRAGON (Aka KAITEI GUNKAN) is a fairly entertaining science fiction from Toho, but its one of their lesser efforts. There is not as much spectacle as can found in THE MYSTERIANS and BATTLE IN OUTER SPACE. The special effects and miniatures are not as colorful and detailed as in previous Toho epics. The big world threat promised by the Muians never materializes, about all they do is sink a Japanese merchant vessel and sink an American navel sub. They also try to kidnap a few surface people, but all that is hardly a reason to destroy a whole civilization. When the submarine Atragon attacks Mu, the Muians make a feeble attempt to protect themselves. Overall, the Muians bark is worse than their bite.
THE MYSTERIANS and BATTLE IN OUTERSPACE are very well paced and exciting films and are recommended to fans of Japanese science fiction. ATRAGON however, was a film I sat through with only mild interest and little enthusiasm.
