The movie starts off with civilians being dropped via helicopter to a hidden location in he desert and put aboard an elevator which takes them nearly 2000 feet beneath the surface, to a self-contained habitat. As they recover from being drugged, they are informed that they have been chosen by the US government to carry on teh survival of the human race--and that they'll be able to go back to the surface in five years, when the radiation has tapered off.
However, they soon learn that they're not the only survivors. There's a huge colony of vampire bats--and as humans are now the only food source those bats want to get to them. But then about an hour into the movie there's a revelation by the psychologist in the group that changes everything--and then they plan to escape.
In the meantime they rig up a trap to electrocute the bats but only manage to destroy a portion of them.
This movie has the feel of OMEGA MAN and SOYLENT GREEN, though without Charlton Heston. But there's a solid cast with Jackie Cooper as the alcoholic rich guy, Alex Cord (GENESIS II) as a writer, Bradford Dillman (BUG!, ESCAPE FROM THE PLANET OF THE APES) as the psychologist, Diana Muldaur (PLANET EARTH) as a Congresswoman and Richard Jaeckel (THE GREEN SLIME) as the lone Army Major.