Undersea Kingdom is a 1936 Republic serial, with the kind of crazed and nonsensical storyline that made these old movie serials such fun. Ray “Crash” Corrigan plays a US naval officer engaged in testing a new rocket-powered experimental submarine. On board are the craft’s inventor (Professor Norton), his mildly annoying son Billy and a glamorous female reporter named Diana. They are investigating mysterious earthquakes, and after diving all the way to the ocean floor they find themselves in the undersea kingdom of Atlantis. Which just happens to look exactly like the kind of country where Republic would film their low-budget westerns. Atlantis is under the sea, but it has sky, and trees, and looks just like home. It’s best not even to try to figure out how this could possibly be.
Atlantis has two rival rulers, one being a noble high priest and the other being the wicked power-crazed Unga Khan. Unga Khan dreams of conquering the upper world, which he intends to reach by means of a huge tower powered by rocker motors. He has advanced technology, including a kind of missile launcher and some extremely silly robots, but the Atlanteans tend to rely mainly on chariots and bows and arrows. Plus they have the Juggernaut, a kind of tank that makes a really cool whooshing noise. It doesn’t seem to do anything else useful, but it is a cool noise.
Unga Khan needs scientific help, so he turns Professor Norton into a willing slave by placing him in the Transforming Room. Meanwhile there’s lots of racing about in chariots. Diana seems to have no idea why she was even included in the cast, since she doesn’t get to do anything at all. Crash gets to do lots, mostly involving hitting people and being heroic.
So will Crash Corrigan save the world from the evil Unga Khan? Well of course there’s not much doubt that he will, but it’s all good fun in a very B-movie way.
It’s not as wildly entertaining as The Lost City, which is by far the best of the serials I’ve seen so far, but if you have a taste for this sort of thing Undersea Kingdom is worth a look. Plus the robots are just amazingly silly looking.