Philip K. Dick 
Defenders [PDF ebook] 

Threatened by impending nuclear war, both the USA and the Soviet Union have retreated deep underground, locking themselves in fortified subterranean bunkers. In their stead, robots they’ve nicknamed "Leadys" have been fighting in their place, waging war against one another for years on end. However, when a group of American troops emerge from their shelter to investigate how the war is proceeding, the Leadys have a strange truth to reveal to them.