Planet (The Underwater Robot)

An Earth-like planet was home to a water-breathing humanoid race which lived in the ocean. Many of them were captured by the Professor's Underwater Robot and enslaved by his gang. The First Doctor, John and Gillian arrived on the planet and were also captured. When they allowed the robot's legs to stop functioning, the slaves rose up against their masters, and escaped when the robot flooded. (COMIC: The Underwater Robot)