Unknown World (1951)

Yikes, but this is a rotten film. The premiss is that in the face of impending nuclear doom we are all to take shelter under the surface of the planet. Luckily for us, the ground beneath our feet is only skin deep; thereafter it is full of beautiful features, cool clear water and an astonishing degree of natural light (emanating from an inexhaustible source of phosphorescent boulders, of course). It's bunkum! The trio of adventurers are as out of their depth as their submarine. Many think that Victor Killan's lack of a credit was due to a blacklist. I'd be inclined to think it was about his seeing this film afterwards and doing some career damage limitation. The effects are pretty low-budget and there is absolutely no chemistry at all between the cast.