Unknown World (1951)
Unknown World (a.k.a. Night Without Stars) is a 1951 independently made, black-and-white science fiction adventure film from Lippert Pictures, produced by Irving A. Block, Jack Rabin, and Robert L. Lippert, directed by Terry O. Morse, that stars Bruce Kellogg, Marilyn Nash, Jim Bannon, and Otto Waldis. The film’s storyline concerns an expedition seeking livable space deep beneath the Earth’s surface in the event a nuclear war makes surface life impossible.
Dr. Jeremiah Morley (Victor Kilian) is concerned about an imminent nuclear war. He organizes an expedition of scientists and has them use a large atomic-powered tank-like boring machine, the Cyclotram, capable of drilling down deep through earth and stone, to find an underground environment where humanity could escape the coming nuclear holocaust.
The expedition (Jim Bannon, Marilyn Nash, Otto Waldis, Tom Handley and Dick Cogan) begins after government funding has fallen through and they are bailed out at the last minute by private funding from a newspaper heir (Bruce Kellogg), who insists on going with them as a lark. Romantic rivalry develops between Bannon and Kellogg for Nash, and two lives are lost to the perils of the dangerous expedition.
In the end the scientists accomplish their goal and find an enormous underground expanse with a plentiful air supply, its own ocean, and phosphorescent light. However, all the lab rabbits brought with them give birth to dead offspring. Through autopsies, it is discovered that this underground world has somehow rendered the rabbits, and hence any other life form, sterile. Dr. Morley is deeply depressed by the news. When an underground volcano suddenly erupts, he fails to enter the safety of the Cyclotram and quickly perishes.
The Cyclotram, carrying the remaining survivors, enters the underground ocean. They soon find themselves rising to the surface of the upper world, having been caught up in a strong upward moving ocean current. They eventually surface near a tropical island.