At the close of World War II, captured German scientists revealed to both the Americans and the Soviets the existence of an unfathomable Underworld on hinted at in legend and folklore. Perhaps driven mad by experimentation with Underworld technology, the Soviet scientist Yerkhov, with the consent of his superiors, takes an artifact known as the Nul Rod and leads an expedition of crack Soviet troops into the depths. The exact fate of the expedition is unknown, but one of Yerkhov’s assistants emerged from a cave in the Nevada desert. His mind broken by his experiences, he gave revealed little reliable intelligence, but did have in his possession a rough map of the expedition’s journey.
Denying the Soviet’s the Nul Rod and establishing an American presence in the Underworld is now our strategic priority. We believe a smaller mission, attracting less attention from the hostile locals, might be able to succeed where Yerkhov failed.
So, I think it would be pretty easy to drop Jason Sholtis's Operation Unfathomable into a 50s sci-fi/monster movie sort of setting. It already has a lot of the right elements. I could see a TV show (by Irving Allen, naturally), something like a cross between Voyage to the Bottom of the Sea and Combat!.