One of the first sci-fi serials made in response to the success of Flash Gordon in 1936, as well as one of the earliest cinematic adaptation of the Atlantis legend and the first to make it an underwater civilization.
Undersea Kingdom (1936)
https://www.youtube.com/watch?v=p9I_TZR-9_M - from the Cult Cinema Classics (3 hour 36 mins long - 720p upscale)
Synopsis:
Following a suspicious earthquake, and detecting a series of signals, Professor Norton leads an expedition, including Lt Crash Corrigan and Reporter Diana Compton, in his Rocket Submarine to the suspected location of Atlantis. Finding the lost continent they become embroiled in an Atlantean civil war between Sharad and the usurper Unga Khan who wishes to conquer Atlantis and then destroy the upper world with earthquakes generated by his Disintegrator.
Directed by B. Reeves Eason & Joseph Kane.
Cast: Ray “Crash” Corrigan, Lois Wilde & Monte Blue.
CHAPTER INDEX:
Chapter 1: Beneath the Ocean Floor
Chapter 2: The Undersea City
Chapter 3: Arena of Death
Chapter 4: Revenge of the Volkites
Chapter 5: Prisoners of Atlantis
Chapter 6: The Juggernaut Strikes
Chapter 7: The Submarine Trap
Chapter 8: Into the Metal Tower
Chapter 9: Death in the Air
Chapter 10: Atlantis Destroyed
Chapter 11: Flaming Death
Chapter 12: Ascent to the Upperworld
Trivia:
• The star of the serial is Ray “Crash” Corrigan, using that screen name for the first time in Undersea Kingdom. The name was created to sound similar to “Flash Gordon”, in one of many similarities. Formerly a stunt man – he was the person swinging on vines in Tarzan the Ape Man – Corrigan went on to use this screenname for the rest of his career in serials and B-Westerns.
• In 1966 scenes from the serial were edited into a 100-minute television film titled Sharad of Atlantis