The Regiments of Night — Brian N. Ball

Beneath the Earth's shattered crust...does the Black Army still wait? After a thousand years of defeat...is the Black Army still fit? Inside their lost underground stronghold...is the Black Army drilling? Archeologists considered the legend superstition and poked about among the surface ruins. Tourists regarded the tales as tourism ads to glamorize a burned-out world. Robots believed only what they saw and none had ever seen such an army. But when a combination of all three tripped the alarm by accident, they found reality turned suddenly into nightmare...as the Black Army awoke to march against the universe!