Toho wasn't just making monster movies in the sixties. They created a series of war films that were quite popular, such as developing several different types of film in the sixties. In 1961, the released Storm Over the Pacific, about the Battle of Midway, as well as The Last War, concerning the outbreak of World War Three. Both were popular. Perennial Godzilla scribe Shin'ichi Sekizawa decided to adapt another novel (as he had with Mothra), this one a fantasy about an undersea kingdom, inspired by the work of HG Wells.
This isn't really a monster movie. The majority is a mystery, in which agents of Mu move among the Japanese people, abducting them. This is a strange foreshadowing of the North Korean abductions of Japanese citizens, which wouldn't happen for a decade, but the Modus Operandi is eerily similar. The film's chief items of interest are Manda, the dragon-god of Mu, which shows up in Destroy All Monsters as well as Godzilla: Final Wars. But this isn't really about Manda, he shows up late and doesn't do much. The focus of the film, is the flying submarine Goten, which received an anime follow up, Super Atragon, and also shows up in Finals Wars. The ship's name was changed to Atragon for the foreign market.
The first half ot the film is abductions and implications, spies, deception, and delving into the past. It's interesting as drama, but has absolutely nothing to do with Manda. The famous ship doesn't even show up until forth-six minutes into the film. The model is pretty well integrated into the live-action with the actors. The film also gets some very well-shot beauty passes. These are a bit more interesting than the usual giant robot deployment scenes.
The overall plot is that Captain Jinguji has been hiding out on an island since the end of World War II, building Atragon so that he can continue the fight against Japan's enemies. The people of Mu have just declared that they will be takng over the surface world, and Atragon seems to be the only thing that can stop them. Atragon is an interesting supersubmarine, with a front drill to supplant the spur on Welles' Nautulus. More than that, though, it can fly. And it has an absolute zero gun, a weapon that freezes its opponents. This shows up on the third iteration of Mechagodzilla in 2002's Godzilla Against Mechagodzilla.
Once Atragion has been shown to the audience, the protagonists are kidnapped and taken to Mu. There, they will be sacrificed to Manda, the god and guardian of the Muvians. The Muvians have submarines with images of Manda on them, and these are the super-weapons that destroy ships. Ironically, Manda has no such breath weapon. Manda is clearly a mationette, surprisingly like Reptilicus, which came out two years previous, in 1961.
If there was any doubt that Atragon was inspired by 20,000 Leagues Under the Seas, it's dispelled when Manda wraps itself around the submarine. Like Nemo, Captain Jinguji electrifies the hull, throwing the dragon off the ship.
The solution to Manda is as simple as using the referred-to but never seen Absolute Zero Gun. Manda freezes, and Atragon can go about the business of destroying the Muvian culture.
As monster movies go, Atragon is unsatisfying. I wouldn't have bothered, but Manda shows up in a couple of films later, and Atragon herself is central of Godzilla: Final Wars. The movie is one of the more popular non-Godzilla films Toho put out. The origin of the Absolute Zero gun was a happy discovery.
Next week, the flashback is over. It's back to New York, in a 1982 American production.