The command struck at me-a mental impulse of immense power. I watched, an observer aloof from the action, as my conditioned-response complex reacted, sensing the fantastic complexity of the workings of the mobile fort that was now my body.

"RETIRE TO POSITION IN SECONDARY TIER!" The harsh order galvanized my automatic responses in instant obedience On impulse, I intercepted the command; then I reached out along my circuits, sent out new commands. I turned myself, faced the violent sun, moved ponderously forward; I halted, pivoted, tracked my guns across the dark sky. Somehow, I had gained control of my machine-body. I remembered the command-the external voice that would have asserted its control But instead, it had cued my hypnotically-produced reserve personality-fraction into active control.

I withdrew, felt the automatics resume control, moving me off to my new station. The aliens were clever, and as thorough as death; I had been tracked down, killed, chained in slavery on a ruined no-man's world; but I had broken the bonds. I was alive, master of my fortress-body-free, inside the enemy defenses!

Later-hours or days, I had no way of knowing-I rumbled down an echoing tunnel into a vast cavern, took my place in a long line of scarred battle units.

"UNIT EIGHTY-FOUR: FALL OUT!" the command voice bellowed soundlessly. I moved forward. Other units moved up, stationed themselves on either side of me. A long silence grew. I was aware that other orders were being given-orders not addressed to me, automatically tuned out by my trained reflexes. Something was going on…

I made an effort, extended sensitivity, picked up the transmission:

"-malfunction! Escort Unit Eighty-four to interrogation chamber and stand by during reflex-check! Acknowledge and execute!"

I heard the snick of relays closing; I was hearing the internal command circuits of my fellow battle units.

I let my automaton-circuits stir me into motion. I moved off, listening as the command voice gave a final instruction to my armed guard:

"Units Eighty-three and Eighty-five: at first indication of deviant response, trigger destruct circuits!"

I saw the turrets of the battle wagons beside me swing to cover me; their ports slid back, the black snouts of infinite repeaters emerged, aimed and ready. The command-mind had already sensed something out of the ordinary in Unit Eighty-four.

I rolled on toward the interrogation chamber, monitoring the flow of reflex-thought in the minds of the units beside me-a dull sequence of course-correction, alert-reinforcements, routine functional adjustments. Carefully, using minimal power, I reached out…

"Unit Eighty-three; damage report!" I commanded.

Nothing happened. The battle units were programmed to accept commands from only one source-the Command voice.

"Units Eighty-three and Eighty-five: arm weapons; complete prefire drill!" The command came. From beside me, I heard arming locks slide open. Together, my guards and I entered the armored test cell.

"UNIT EIGHTY-FOUR! DISARM AND LOCK ALL WEAPONS! RESPONSE-SEQUENCE ALPHA, EXECUTE!" The voice of the Interrogator rang out.

I watched as my well-drilled reflexes went through their paces. I would have to move with great care now; every action was under scrutiny by the enemy. Another command came, and as I responded, I studied the quality of the Interrogator's voice. It was different, simpler, lacking the overtones of emotion of the Command-mind. I reached out my awareness toward it, sensed walls of armor, the complex filaments of circuitry. I followed a communications lead that trailed off underground, arose in a distant bunker. The intricacy of a vast computer lay exposed before me. I probed gently, testing the shape and density of the mechanical mind-field; it was a poor thing, a huge but feeble monomaniac-but it was linked to memory banks…

I felt a warning twitch of alarm in the moron-circuits, caught the shape of an intention-Instantly I shunted aside its command, struck back to seize control of the computer's limited discretionary function. Holding it firmly, I traced the location of the destruct-assembly that it would have activated, found it mounted below my brain, disarmed it. Then I instructed the Interrogator to continue with the routine checkout, and to report all normal. While it busied itself in idiot obedience, I linked myself to its memory banks, scanned the stored data.

The results were disappointing: the Interrogator's programming was starkly limited, a series of test patterns for fighting and service machines. I withdrew, knowing no more than I had of the aliens.

The Interrogator reported me as battle-ready. On command, I rejoined my waiting comrades. An order came: "ALL UNITS, SWITCH TO MINIMUM AWARENESS LEVEL!"

As the energy quotient in my servo-circuits dropped, the sensitivity range of my receptors drew in, scanning from the gamma scale down through ultra-violet, past infra-red, into the dullness of short-wave. Silence and darkness settled over the depot.

I sent out a pulse, scanned the space around me. The clatter of the Command-voice was gone. I was alone now-I and my comatose comrades-in-arms. There were ninety-one units, similar to myself in most respects, but armed with a variety of weapons. Small, busy machines scurried among us, carrying out needed repairs. I touched one, caught vague images of a simplified world-image, out-lined in scents and animal drives. I recognized it as the brain of an Earthly dog, programmed to operate the elementary maintenance apparatus.

Reaching farther, I encountered the confused mutter of a far-flung communications system, a muted surf-roar of commands, acknowledgments, an incoherent clutter of operational messages, meaningless to me.

I touched the mind of the fighting machine beside me, groped along the dark passages of its dulled nerve-complex, found the personality center. A sharp probing impulse elicited nothing; the ego was paralyzed. I withdrew to its peripheral awareness level; a dim glow of consciousness lingered there.

"Who are you?" I called.

"Unit Eighty-three, of the line." The reply was a flat monotone.

"You were a man-once," I told it. "What was your name?"

"Unit Eighty-three of the line," the monotone repeated. "Combat-ready, standing by at low alert. Awaiting orders."

I tried another; the result was the same. There was no hint of personality in the captive brains; they were complex neurotronic circuits, nothing more-compact, efficient, with trained reflex-patterns, cheaper and easier to gather from the warring tribes of Earth than to duplicate mechanically.

I stirred another quiescent brain, probed at the numbed ego, pried without success at the opaque shield of stunned tissue that surrounded it. It was hopeless; I would find no allies here-only slaves of the aliens.

Free inside the alien fortress-in a flawless camouflage-I was helpless without information. I needed to know what and where the Command-voice was, the disposition of other brigades, the long-range plan of action, who the enemy was that we fought on the fire-shattered plain-and on what world the plain lay. I would learn nothing here, packed in a subterranean depot. It was time to take risks.

An impulse to my drive mechanism sent me forward out of the lineup; I swung around, moved off toward the tunnel through which I had entered the cave. In the utter silence, the clash of my treads transmitted through my frame was deafening. I filtered out the noise, tuned my receptivity for sounds of other activity nearby. There was none.