"Undersea Kingdom" could be compared to Universal's popular "Flash Gordon" serial released the same year. Instead of having the story take place in outer space, Republic stages this one at the bottom of the sea in the lost continent of Atlantis complete with a mad man trying to take over the world and a similarly named hero.
Unga Khan (Monte Blue) has harnessed the atom and is causing earthquakes across North America. Scientist Professor Norton (C. Montague Shaw) has invented a ray that will counteract the earthquakes which he believes are coming from the ocean floor,
As luck would have it the ever resourceful Norton has also invented an atomic powered submarine with which he plans to descend to the ocean floor and discover the source of the carnage. He forms a team which includes "Crash" Corrigan (Ray Corrigan) a naval lieutenant and a muscular athlete (who gets to run around without his shirt for most of the story), Diana Compton (Lois Wilde) the ever present newspaper reporter, young Billy (Lee Van Atta) Norton's son, Norton's assistant Joe (John Bradford) and for comic relief Briny (Smiley Burnette) and Salty (Frankie Marvin).
When the sub descends into the ocean it is discovered by Unga Khan who using a tractor beam pulls the crew into the undersea world of Atlantis. There, Crash and the gang discover that there are two warring factions..Khan's Black Robe Guards and the White Robed followers of Sharad (William Farnum). The Black Robes posses a tank-like machine called the Juggernaut and an army of walking garbage can robots called Volkites.
Anyway, to make a long story short, Crash becomes leader of the White Robes' army and Unga Khan captures Professor Norton and alters his mind so that he obeys without question. Khan plans to have Norton produce the priming powder that will ignite the rockets that will propel his tower to the surface and thereby enable him to take control of the world. Well, over the course of the 12 chapters, Crash and the gang escape numerous life threatening situations and ultimately save the world.
This serial is full of contradictions. Firstly, the Black Robes have harnessed the atom, the Volkites and the Juggernaut each possess deadly ray guns yet the soldiers ride in horse drawn chariots or ride horses and fight with swords, and they even have guided missiles. Secondly, Norton's atomic powered submarine is left in the hands of two bumbling assistants? Credibility gap here?
There are some good (and some cheesy) special effects. The two sieges on the White Robe city are well done, although I don't know what good that so-called flame thrower is. The flying craft seems to be going in circles and the "Tower" looks really cheap when it appears on the surface.
A word about the rest of the cast. Boothe Howard and Lon Chaney Jr. (wasted again) play Unga Khan's chief henchmen and Lane Chandler plays Sharad's assistant. In an offbeat bit of casting, Raymond Hatton plays a bad guy and John Merton a good guy. Hatton of course is best remembered as the crusty old sidekick in dozens of "B" westerns. The muscular Merton (sans moustache) was usually cast as a villain. Burnette and Marvin are given little to do and disappear for several chapters at a time.
For Corrigan, this was his first starring role. He would play the lead in Republic's "The Painted Stallion" serial in 1937 as well as, beginning a long run as Tuscon Smith in the long running "Three Mesquiteers" series.
