The Guardians' range was simply too long, allowing the Zerg Swarm to neutralize the anti-air turrets on the walls with almost zero casualties. However, the battle within the fortress walls could not rely on Guardians.
As Zerglings began pouring into the base, the nature of corridor warfare allowed the sheer strength of the Space Marines to be fully realized. As long as there were three or more Astartes defending a single corridor, they could grind down tens of thousands of swarming units. Not to mention the presence of local PDF forces and various armored assets.
†Kans, stop using Zerglings. Send in the Roaches.†
The Overmind had played enough games of this genre to know the score. A few tanky units in narrow corridors could wreak havoc—whether it was Vermintide, Darktide, or Space Marine 2, using fragile units like Zerglings to rush a corridor was just sending them to their deaths. Only a combination of massive numbers of Roaches, Hydralisks, and Banelings could truly disgust the Space Marines.
As expected, once the Roaches joined the fray, the tide of battle shifted. Even the Astartes' bolt shells struggled to eliminate Roaches quickly. Relying on their thick chitinous carapaces and rapid regeneration, the Roaches acted as living meat-shields.
Furthermore, when the first Roach variant—a Vile—spat its acidic saliva, a Space Marine dodged the strike, only for the acid to splash onto the Leman Russ tank behind him. Seconds later, the crew inside felt a wave of malaise; unknown microorganisms had invaded their bodies through the air filtration system. Though it didn't kill them instantly, it dulled their senses significantly. The firing rate of the Leman Russ plummeted.
Seeing that bolters and heavy bolters couldn't put the Roaches down, one Hands of Judgment Marine drew his chainsword and revved it as a Roach closed in. The grinding of Adamantium teeth against chitin sent sparks flying everywhere. The Roach lunged with its claws, but the Marine avoided the blow with a swift backstep. He then gripped his chainsword horizontally and plunged the high-speed blade into the Roach's head, pureeing its internal organs.
†Oh ho, quite the tough customer. You can kill one Roach, sure, but how many can you kill in a row?†
Though Roaches were more expensive than Zerglings, they were still ultimately "trash" units in the eyes of the Swarm. More Roaches flooded the corridor, their bulk filling the passage three or four abreast. Even in death, their corpses provided cover for the Zerg units following behind.
The corridors were slowly falling. The Space Marines began taking casualties; a few were killed instantly by Hydralisk spines piercing their helmets, but more fell to the Banelings hidden within the swarm. In just one hour, over a dozen Space Marines had fallen, their bodies trampled by the advancing Swarm.
"They're putting heavy units in the front to soak up our fire! Dammit, these things can take a direct hit from a Leman Russ battle cannon and keep coming!"
"But they can't fly! Blow the corridor!"
Charges had been pre-planted at the base of the corridor. Following the commander's order, a massive explosion erupted, killing a swarm of Zerg and causing the floor to collapse. Below was a pitch-black abyss dozens of meters deep, filled with various utility pipes. The leading Zerg units fell into the pit, unable to react. They weren't killed by the fall, but they certainly couldn't climb back up.
"They can't climb walls?"
"Interesting. Tyranid Hormagaunts are quite adept at climbing."
Tyranid units were mostly humanoid or upright in structure, much like Xenomorphs; their talons allowed them to scale cliffs with ease. Zerg units, however, were generally poor climbers unless they belonged to specialized climbing or leaping strains. From this depth, Roaches and Hydralisks would have to burrow their way out, though Zerglings could manage to scramble up using protrusions in the walls.
For the time being, the Zerg were blocked from this particular corridor. Even if Zerglings tried to leap across, they would be picked off by the PDF soldiers guarding the other side.
Ares listened to the reports, his brow never unfurrowing. "I don't think they are Tyranids. Is the Astropath of this planet still alive?"
Astropaths are sanctioned Psykers of the Adeptus Astra Telepathica; they can send instantaneous communications through the Warp. Every Astropath is a precious resource, but typically, a world will have one or more.
"Yes, Captain Ares. He is still with us."
"Send a message to the Astropaths of other Imperial worlds. Inform them of the existence of this new xenos breed. Their appearance is too suspicious; I do not believe they have only appeared on this single planet."
Captain Ares spoke with extreme gravity: "It is highly likely they have already devoured other Imperial worlds. They differ from the Tyranids, but they may be even more dangerous."
Tyranid warfare was far less orderly than what the Zerg were demonstrating. Seeing the enemy prioritize heavy units for corridor breaches told Ares that his losses would be severe. Fortunately, the PDF base was large, food supplies were plentiful on this Agri-World, and decades of peace meant the armories were overflowing. As long as they kept casualties at a manageable level, they could hold for a long time.
What Ares feared most was that they couldn't keep the casualties down.
"The enemy hasn't shown a commander even now. This is a serious problem."
Ares made the same fundamental mistake as previous enemies: the commanders were always in the sky, yet they never prioritized eliminating them. While the Overmind and Kans were micro-managing the Swarm, their control would be severely crippled without the assistance of Overlords. However, Ares lacked the means to send Thunderhawks to hunt them down.
The Hands of Judgment had already lost.
"Now we can only wait for the Chapter Barque's support. Meanwhile, notify the fleet in near-orbit: orbital bombardment must not stop. There may not be many units in the occupied zones, but any kill reduces the pressure on us."
The orbital bombardment resumed. The newly spreading Creep was once again blasted by energy beams, causing the Overmind to scowl.
†Truly a successor Chapter of the Fists—they're too good at defending. I can't find a single breachable corridor, and now there's more orbital fire. Kans, set the Nydus Worm entrance at the Nydus Gate and the exit near the enemy base. We're not going over the ground; we're delivering the Swarm directly to their doorstep.†
†Once we have total air superiority, have the Overlords drop Banelings directly into the base. Mutalisks will attack anything that leaves cover to protect the Overlords. Nydus Worms will attempt to open paths inside the base. Even if the walls are thick, the worms should be able to chew through. If there isn't a corridor, I'll make one.†