Philip K. Dick 
The Defenders [EPUB ebook] 

In The Defenders, the Soviet and American survivors of a nuclear holocaust have created vast underground tunnels, so as to continue the war on the surface via remote control robots. When a robot from the surface is found not to be radioactive, a team of American scientists returns topside to investigate this anomaly. Expecting to see massive devastation, the scientists are unprepared for the shocking truth that awaits them.