City Beneath the Sea - 1971

A small grouping of colonists that are 21st century inhabit an underwater city called Pacifica. Originally intended as a purely scientific setup, the U. S. government wants to stash all its gold reserves from Fort Knox there, together side a wonderful new radioactive element. The brother of the returning commander of Pacifica intends to steal the stone and also on top of that, the town faces destruction via an asteroid from outer space