Undersea Kingdom (1936) is one of those great science-fiction "cliffhanger" serials that used to play before theatrical films in the 30s and 40s. In this a fun, 12-part adventure, Ray "Crash" Corrigan plays a naval officer/hero who accompanies a professor and crew on a submarine to discover the cause of recent earthquakes. The crew quickly discovers that the quakes are originating from the lost civilization of Atlantis. When they arrive in the undersea city, they are immediately captured by Unga Khan, evil ruler of Atlantis. The remainder of the story concerns the ongoing battle between Kahn's forces, the crew of the submarine, and the kind-hearted citizens of the Atlantis Sacred City.
As with most serials, you have to check your brain at the door when you watch UNDERSEA KINGDOM and just enjoy the fun story and action. Typical for these programs, the acting and dialog is laughably bad. The effects and costumes are pretty silly (and are reused several times) and the plot has HUGE gaps in logic. But, that is all part of the fun... and there are great things here as well, including an early role for Lon Chaney Jr. and a wonderful design for the evil robot soldiers.