THUUUM. A roar filled Marcos's ears as the mortar blast catapulted him forward. His Wheel's gyros groaned ominously but kept him upright. Then the pressure wave was past, Marcos still improbably upright on his craft.

Next came a softer rustling, as of a flock of birds taking flight. Shrapnel. He registered a dull ache on his torso and a searing pain across his right quad. Body armor caught the first fragment, he'd have a bruise but no internal damage. The other had sliced through his STF impregnated kevlar and tore skin, though he didn't feel a lot of blood. Hopefully the leg would hold until he could get to safety.

Looking around he saw a handful of other personnel on Wheels, though fewer than he'd expected; apparently other vehicle pods were also targeted in the first round of shelling. Most troops were sprinting on foot toward central, hoping to outrun the assault. The ones not wearing armor might have a chance but the others were just too slow.

Between explosions Marcos could hear the throaty buzz of miniguns, the blur of gunfire merging into a guttural vibration. Good to hear that the base defenses were active, but bad that there were enough targets in range to keep the weapon firing. Maybe gun rats? That's what he'd use for an assault on the base, if they were legal. Or he had plausible deniability.

Marcos toggled his ghost voice to command mode, if his guess was right there was no time for a human in the loop on this order. "Target: All units. Command: activate mimicry camo subsystem. Execute."

Marcos pulled his hood up as the rectangular blotches of colors on his fatigues flowed into something more organic: eye spots, noses and other strange blobs swam across his clothing. To a human his outfit looked like a psychedelic nightmare, but he wasn't trying to fool a human. Gun rats typically used rudimentary machine vision to aim for the head, the trick was convincing them your head was somewhere else. Preferably somewhere with a hard plate.

A few moments later his suspicion was confirmed by an alert flashing on his HUD: PASD SWARM DETECTED. He called up a perimeter camera feed and overlaid it in one corner of his glasses, splitting attention as he slalomed his Wheel at breakneck speed between mortar craters.

What he saw in the security footage worried him. A steady trickle of green and brown bots were probing the kill zone, emerging from the underbrush at regularly spaced intervals. Zooming in on one Marcos saw a bog-standard gun rat: a slender 4" long plastic tube formed the spine of the creature, housing both its electronic guts and serving as a single-use barrel for a lone bullet. A plum-sized bulb mounted atop the front of the tube carried an imaging sensor, a pair of microphones, and an array of infrared LEDs for basic dark vision. Six plastic legs spaced equally down the tube propelled it forward faster than a man could run.

He watched as the nearest base cannon locked on and a lead rain fell upon the creature, filling the air with a shower of mud. Three legs were shot off, though the rat still shambled forward with a jerky unbalanced gait. Another bullet grazed the tube body, leaving a deep scar. Finally one scored a hit on the sensor pod and the bot collapsed in a shower of cheap plastic. Zooming back out Marcos watched as more rats emerged to the left and right, mapping out the coverage of the base turrets.

Polypedal autonomous strike drones (PASDs, colloquially "pasties" or "gun rats") are anti-personnel weapons originally developed by Burmese rebels. They're light and easy to haul around, once deployed they can move under cover of underbrush, and a slender body makes them a hard shot even for AI-assisted targeting. While the individual components are cheap and readily available on the open market, the assembled package breaks every international convention on autonomous weapons.

Still, by itself a gun rat is not the most fearsome adversary - the plastic barrels are prone to defects and destroyed in the act of firing. Add in poorly calibrated sensors and the hit rate is barely 50%. But no one ever sees a single gun rat; they're sold by the case. A four-man squad can pack in and deploy a swarm of thousands anywhere in the field, purchased for less than the price of a budget assault rifle.

The gunfire stopped, no new sacrifices being offered up to the thirsty turrets. Then all at once an undulating carpet of green and brown tubes boiled out from the jungle. The robot tide was relentless, for each rat shot down two more took its place. Marcos didn't need an AI forecast to tell him the turrets were overwhelmed. He dismissed the perimeter footage and focused his attention on the path in front of him; getting to the bunker at Central was his only chance of staying alive.

More crimson had bloomed across the intervening ground. The glasses told him this was a smaller volley. Hopefully that meant the base drones were doing something. Still, the ground between him and Central was an almost unbroken sea of pink and redNo problem for him - with his Wheel he'd pass through well before the next flight hit. The people on foot though, they were trapped.

With luck they could at least be ransomed off by insurgents rather than gunned down by an inhuman firing squad. He broadcast a warning as he passed: "All personnel on foot seek immediate shelter, PASD perimeter breach imminent. Standard protocol - seal all doors and hunker down until all clear given."

Marcos pushed harder on his Wheel, overriding the complaining safety systems. He zipped past the second ring of the compound and banked left, happy to put a building between his back and the cresting wave of killer robots. Scattered pops rattled out as gun rats acquired their first targets. Hopefully they were hitting armor instead of grey matter.

Riding at top speed required a zen-like focus. He fell into a groove on the Wheel, carving effortless arcs around the fleeing soldiers and new rubble. He was almost to the first ring of buildings, finally clear of the falling shells. The curved edge of Central peaked out from behind the nearest structure. He turned the corner and saw a sea of thick mud, then shifted his weight to slow down before he was mired. Too late he remembered the shrapnel hit to his thigh; the leg faltered as he pushed on it and he couldn't brake in time.

A spray of muck flew out as the Wheel locked up and skidded sideways. Then he hit a buried root and it was over, his body tossed forward from the abrupt deceleration. He went down hard this time, his right shoulder taking the brunt of the fall. He hoped the loud crack was gunfire. Doubted it.

Marcos came to rest face down in the muck. He tried to push himself up and fell back again, his right arm non-responsive. No time to worry about it now. He rolled to one side, then forced himself up with his left arm, straining against the weight of his armor.

Mud coated his glasses - he shifted alerts to auditory and stuffed them in his pocket. His Wheel had crashed a few feet behind him, half buried in the sludge with the axle bent at an odd angle. He'd have to make this last dash on foot. He started slow for the pain, but quickly sped up to a trot, his leg throbbing with each impact. Central was half a football field feet away, and its blast doors were slowly closing.

An audio alert reverberated in his skull: PASD UNITS DETECTED.ADVISE SEEKING SHELTER.

As if he needed another reason to move faster. At least the gun rats weren't snipers, they needed to get close with their low accuracy. Were he uninjured, beating them to Central would be no problem. But with his leg? Time to find out. He gritted his teeth and broke into a run.

PASD UNITS CLOSING ON POSITION. SEEK SHELTER NOW.

He was coming up on Central fast, but the doors had almost closed. Wouldn't do him any good to outrace the rats if he couldn't get inside.

"Officer Oliveira requesting three second pause in blast door cycle."

"Affirmative. Cycle paused."

The doors stopped.

PASD UNITS AT APPROACHING RANGE. PREPARE FOR GUNFIRE.

He made a final push, closing the last ten strides to the door.

The voice came again: PASD FIRING NOW

Damn. Two more strides to go. He knew the gun rats would have to drop to stabilize the shot, he might still make it–

POP, POP, POP. Marcos collapsed like a marionette with its strings cut, halfway through the door.