Underdog (1964)

Season 1: Episode 25

The Emperor and Empress of Maldamere have a scientist who has created a tidal wave making machine, and plan to use it to destroy the surface world. Concerned about the giant waves that are threatening the world, Sweet Polly Purebred and Professor Moby Ahab- a noted oceanographer- head for the South Seas to investigate. But their trip to the South Seas are being watched by the evil monarchs of Maldamere. The Empress orders the release of her army of giant whales to stop Polly and the Professor. Seeing the attack, Polly calls for Underdog who foils the whale attack. Angered, but not willing to admit defeat, the Empress orders her guards to capture Polly and the Professor in their submarine. The very moment that their bathysphere reaches the ocean's bottom, Polly sees a strange and horrifying sight.