The spy approaches the target building under cover of darkness, taking a zigzag path to avoid well-lit areas and sentries. He selects a handy vantage point next to a dumpster, taking cover behind it when he hears the footsteps of an unseen guard. Once the coast is clear, he is on the move again - trundling along on four small wheels.

This is no human spy but a machine, a prototype in the emerging field of covert robotics. It was being put through its paces at a demonstration late last year by Lockheed Martin's Advanced Technology Laboratories at Cherry Hill, New Jersey. The company wants to design autonomous robots that can operate around humans without being detected...