Second Variety by Philip K. Dick.

"Second Variety" occurs in the aftermath of an extensive nuclear war between the Soviet Union (sometimes referred to as Russia) and the United Nations. Early Soviet victories forced the North American government and production to flee to a Moon Base, leaving the majority of their troops behind. To counter the almost complete Soviet victory, U.N. technicians develop robots, nicknamed claws—the basic models are "a churning sphere of blades and metal" that ambush their unsuspecting victims "spinning, creeping, shaking themselves up suddenly from the gray ash and darting toward… [any warm body]." U.N. forces are protected from the claws by a special radiation-emitting wrist tab. Within six years, the sophisticated and independent claws have destroyed the Soviet forces, repairing and redesigning themselves in automated underground factories run without any human oversight.

The U.N. forces receive a message from the Soviets asking for a policy-level officer to go to them for a gravely urgent conference. The U.N. victory was costlier than they had expected. Major Joseph Hendricks is sent to negotiate with the Soviets. En route to the rendezvous, he meets a small boy named David who asks to accompany Hendricks. When they near the Soviet bunker, soldiers immediately kill the boy, revealing him to be an android. The claws' development program has evolved to develop sophisticated robots, indistinguishable from humans, designed to infiltrate and kill. The three Soviets met by Major Hendricks—soldiers Klaus, Rudi, and a young woman named Tasso—reveal that the entire Soviet army and command structure collapsed under the onslaught of the new robots - they are all that are left in the command center.
From salvaged internal metal identification plates, two varieties are identified: I-V, a wounded soldier, and III-V, David. II-V—the "second variety"—remains unknown. The different models are produced independently of each other in different factories. The Soviets also reveal that the U.N. protective tabs are ineffective against the new robots. Hendricks attempts to transmit a warning to his H.Q. bunker, but is unable to do so.