The moaning of wounded soldiers carried on the wind. Mingling eerily with the utterly alien chittering, creaking, and growling of the tyranid beasts, lurking, waiting, building up forces, just out of range of teh base weaponry. The acrid taste of burning promethium scorched the back of the survivors throats. The occasional man or woman vomited where they stood, sighting along their battered lasguns as droplets of blood or ichor found its way into their nose or mouth. Battered, beaten, and weary, the troops ducked in an instinctive reaction as the vulture laden with promethium fuel barrels screamed off into orbit, Barely dodging an Arvus Lighter as it made its approach.
"Here they come! Fire at will!" The shout echoed down the line of nervous troops.
Las bolts flashed into the darkness approaching. Cutting down the smaller, weaker termagants and hormagaunts. Hold the line. That was their mission. No option to retreat. No chance to make for orbit. Just plunder the planet, at the cost of lives. Every soldier knew it. Those of a faithful disposition began to mutter hymns. The more practical amongst them began regimental chants, limericks, ditties, or hummed favourite tunes.
A deafening roar opened up behind the firing troops. The armour was adding it's weight of fire. Punisher cannons glowing yellow in the deepening darkness as they fed the one thing they loved to fedd the Tyranids. Death. Heavy bolters mounted on teh tanks, as well as crew served weapons chattered. A roaring scream sounded as the Arvus took flight, powered to full throttle, and exploded! Burning promethium cascaded upon the hapless defenders, igniting human torches, burning holes in the Tyranid advance as syapse creature were killed, and the smaller bests attempting to get away from the falling death.
Taking advantage of the wavering line, the remaining armour seized the initiative and gunned their engines, pausing their guns to reload only, they pushed through the corpses before them, and advanced towards the swarm. Emboldened by the armoured advance, the crew served weapons teams ceased fire, and displaced to maintain a line with the armour. A vulture touched down in the opened skyshield landing pad, and slowly raised its defenses as fuel extraction commenced.
Seeing the success of the armour, sergeants rallied those closest to them, and organised them into ranks. Marching forwards slowly, and carefully, the defenders started to push teh Tyranids back. Fluidly spreading out, the order "First Rank, FIRE! Advance. Second Rank, FIRE! Advance." Rang against the walls they had left, and those that surrounded them.
Hope grew. THey were driving the Tyranids back! They could survive another day, The vulture screamed away as another began landing sequences. It touched down, hard, and kept moving. Sliding and screaming its way along the landing pad. Nothing was able to arrest teh stricken craft, that can in too fast, and too steep. As if in slow motion the craft began it's crashing journey to the ground, taking emplaced weapons to the ground. As another Vulture landed successfully several things happened at once.
Massive, fleshy objects began hitting the ground, the buildings, ammo dumps, an enormous explosion engulfed the base of the dam, sending cracks racing along the surface as the dead vulture came to rest in teh middle of the fuel dump for the armour. Beyond the walls, trees came crashing down as beasts nobody had seen on planet before came racing towards the confused defenders. Two of teh remaining five tanks vanished underneath the bulk of the fleshy objects. Sphincters opened up, allowing the scariest creatures to be seen emerged. Carnifexes, but different. Huge ram-like parts jutted from their shoulders, over their heads. Prehensile tails swinging pulped troops caught too close, or jerked armour about as if it were made of paper.
From the edge of the forest, more carnifexes appeared, almost skirmishing for the creatures behind them. The vulture took off, dodging incoming felsh-pods and fire from artillery creatures as the clambered into position. Incoming ships risked everything to retrieve the precious fuel, and make the sacrifices of their comrades worth something.
Crushing the retreating Imperial vehicles beneath hooves far larger than they had a right to be, the knight-sized beasts began to vomit forth stream of some sort of fuel, until the they belched, the vibration of which caused a spark between their teeth. Again, Imperial troops found themselves covered in fire, being consumed as if there were no tomorrow, which, would be accurate for these poor souls.
Several types of screaming began to compete with each other. The scream of biological creatures used as ranged weapons, the scream of engines as craft leap off the landing pad so another may take it's place, the scream of new, chitin covered pods that either impacted with such force they dug deep into teh ground, obliterated structures, or gouged huge channels in teh face of teh dam, sending large sheets of rockrete tumbling down.
The pods that did not implode, explode, or rupture on contact disgorged more of the battering ram Carnifexes, which ran head first at the crumbling structure. Precious few defenders remained. Each one engaging where they could do the most good. The sky darkened as winged Tyranids began to fill teh air over the dam. Large winged creatures threw themselves into it, doing considerable damage to themselves, as well as the facing. Vultures began exploding in the air, engine intakes clogged with flesh, fuel tanks ruptured by acidic attacks.
The final nail in teh coffin of the defenders came in teh form of a vulture, clearly in trouble as it spiralled out of teh sky, and collided with teh promethium heavy ship preparing to take off. There was nowhere safe, nowhere to hide. Tyranid or Imperial defender, scrap metal and burning promethium rained down. The battle was ended, those Vultrues that could, returned to orbit. The Imperium left the planet, and, with it, the Promethium reserves that could have turned the tide...