The Devastator Marines opened fire with their plasma cannons. Blue arcs of superheated plasma sailed over the crimson rust of the pollution of war that had been kicked up into the atmosphere. The smell of copper blood, engine oils and acrid black smoke mixed with the sulphur compost perfume of biological corpses rotting in the heat as the forces battling around them disturbed their final resting place.
"Too late." Said Ferrum Umbra as he watched the the first plasma ordinance fall short of a position nearby his own. He had committed the bulk of his forces to this battle knowing that aid would come for the Death Korps. He had jammed the planetary comms lines, but nothing in war ever works perfectly. Not even the will of iron. He grumbled at the new development.
"Rear units" he voxed. "Move up. Forward forces, turn and take the insects." He visually chopped the command in the air with his power axe so that all could see.
"Terminator units… On me."
The cries of bayoneted cultists died off as they began to turn and fall to the rear.
"They're retreating." Said a guardsman.
"No." Said another. "They're regrouping."
Scores more of the cultists began to emerge as if from nowhere. They scurried out of the scrap metal and twisted remains of the forge wreckage and scurried and scampered out of hatches attached to underground compounds dotted across the landscape. The guardsman gulped as they realised the enemy had been beneath them the whole time, tunnelling to underpin the trench and rear bases. The presence of the new additions to the battlefield had at least temporarily stalled that plan, but a worthy enemy is one who adapts.
Without warning, cries of human pain and agony came blaring down the line as a typhoon of body parts began to spring above the height of the trenches. The bug zapper electric arc of the power axe grew louder as the threat came closer to reuniting with his traitor counterparts. From the other side; the high pitched hiss of gases being projected underpressure followed by the rush of heat as their fumes ignited to consecrate the human obstacles before them in the trenches pierced the sounds of human decimation.
"Get it done quick." Said Ferrum Umbra over the vox to his Terminator clad battle-brothers.
Their response was to introduce bolt rounds to the massacre.
"Objective complete." He heard shortly after.
"Good," he replied. "The real objective lays ahead."