Zedís freebooters, thus, had free reign of the sky. They could soften up the targets, raining munitions down on the obvious targets, tanks parked in their lots (not that the moving ones presented much more difficult a target), guard units scrambling about and putting up symbolic resistance. Their own tracers truly only guiding ork bombs into newfound targets.
When Zed landed his troops, that little bit of knowledge he had acquired through the spoiled work of the servitor would greatly swing the battle into his favor. The 5000 Orks were now more than enough to crush the remaining resistance.