"The Mysterious Island" (1929) MGM Technicolor Part-Talkie Adventure Photoplay

On a volcanic island near the kingdom of Hetvia rules Count Dakkar, a benevolent leader and scientist who has eliminated class distinction among the island's inhabitants. Dakkar, his daughter Sonia and her fiance, chief engineer Nicolai Roget, have designed a submarine boat which Roget pilots on its initial test voyage shortly before the island is overrun by Baron Falon, once Daggar's friend, and now the new despotic ruler of Hetvia. The Baron has Dakkar and his daughter tortured so that Dakkar will reveal all his discoveries. Dakkar is able to escape with the intervention of his loyal men. But Falon sets out after Roget and Dakkar using the Count's second submarine. The two underwater craft dive very deep to the ocean floor, where they discover a strange land populated by dragons, a giant octopus, and an eerie, undiscovered humanoid race.