There have been quiet a few requests for this one, so I've decided to at least attempt it. But given that all I know of the Warhammer universe is what I read in the three Titan TPB's, it's unlikely that it's going to be that accurate.
First Contact 26:
Deus Mechanicus
"God is mocking me..." Six protested to an uncaring universe in general.
It had taken her a long time to convince the others that she shouldn't be boxed, that the on-going dreams weren't the first signs of something darkly referred to with hushed tones as rampancy. But as last she had succeeded, and had been given command of a small fleet sent to scout ahead of the Colonial Remnants projected path, out of the small star cluster they had originated from and into its parent galaxy itself. What they had found had shaken he entire Cylon race to their collective core; millions of human-inhabited worlds, locked an a galaxy-wide war of annihilation with at least two other races. Armies numbering in the trillions clashed across a hundred thousand light years, while fleets who's smallest escort dwarfed even the largest Battlestar battled through the eternal night of space. The idea of getting involved in such a conflict seemed all but insane, but God's law was strict: all human life had to be eliminated.
A world had been selected, on the edges of human controlled space, and a expeditionary force assembled ready to lead the first raid, mainly to gather intelligence and any new technology that could be used against both the Colonials and this new 'Imperium of Man'. Six couldn't help but fell that the fact that she had been given command of the mission was just another plot by the Cavils; if she succeeded, then they would claim that it was only by following their plan. And if she failed, they would use her as their scapegoat. Either way, it was a win-win situation for her old adversary. Still, it felt good to be back on the command deck of a Basestar, serving both her people and God's will.
Arriving over the target word, they had been surprised to find other ships had already arrived; massive transports bearing the markings of the Imperium. It would have been foolish to engage them, so she had ordered her fleet to the other side of the planet in the hopes that they might not be noticed. Landing an entire army of Centurions had taken time; they had never before been forced to deploy ground forces in such numbers. Still, they had gotten down, setting up a pre-fabricated field-base in the middle of an area of scorched earth measuring some twenty thousand square miles. The original scout ship's scans had shown a world covered in lush rainforests: something had burned the vegetation, searing the very soil. The air was thick with carbon smog, forcing Six and the other infiltrators to don environment suits if they wanted to venture outside the sealed bunker.
Orbital scanners detected them first, and Six had sent a squad of Centurions out to investigate: none had returned. The last few images they had sent back showed towering humanoid figures who's thick armour shrugged off the most powerful Cylon weapons. A larger patrol had been sent, only to be totally over run by the same force, this time backed up by lumbering armoured vehicles. Six had been at the point of sending a third, much larger detachment armed with the very latest in tactical nuclear weapons, when their seismic scanners had picked up the slow but steady approach of something much, much bigger. Six had made her way up to the observation tower high above the base to see its approach with her own eyes.
It approached through the thick smoke, every step shaking the ground. Even the most powerful optical enhancer showed only a dark shape in the clouds, but even that sent a shiver of foreboding down Six's spine; she couldn't shake the feeling of impending doom. She tried reaching out across the electro magnetic spectrum to see if there was some controlling computer that she could hack into. What she found sent her reeling back as if she had been burned: what ever it was that was slowly approaching, it was old and powerful, a machine that lived only to kill on a scale unimaginable to even the Cylons. Sensing their leaders fear, one of the other infiltrators ordered all of the remaining Centurions to attack, sending everything they had into the fight.
Fire and noise filled the air as the two armies collided in an orgy of death and destruction. Through overwhelming fire-power and numbers, the Centurions were finally able to bring down a few of their smaller adversaries, but even their pocket-nukes had little or know effect against the monolithic shape that was finally becoming clear through the fog. It was roughly humanoid in shape, but stood as high as a skyscraper. A crude head jutted out from between, each arm ending in a different weapon while more sat in massively armoured housing built into each high shoulders. It stalked the battlefield like a vengefully god, striking out with unimaginable power, crushing Centurions under its feet by the dozen.
"I am Ervin Hekate, by the grace of the God-Emperor, Princeps in the Titan Legion." A unmistakable human voice echoed across the every radio frequency, "Who dares to challenge the Imperium's control of this world?"
"I am Six of the Cylons." The Hero of Caprica managed to sound more confidant than she actually was, "Our God; the one, true God, demands the extermination of the race of Man. Who do you think you are to stand in the way of our holy crusade?"
"We are Titans, shakers of words: Where we step, the earth shudders; where we rage, cities die." Hekate's voice grew deeper; as cold and hard as tempered battle-steel, as the colossal and ancient sentient war-machine he was bonded too spoke directly through him, their voices merging into one, "I am Imperius Dictatio: let my enemies fear me, let their deaths be deaths of fire at my steel hands. And by the Gods of Mars, LET ME SERVE AS A TITAN UNTIL THE END OF MY DAYS!"
The Titan's massive left arm swung round with amazing grace for such a large machine, the maw of its directed energy weapon pointed directly as the lightly armoured Cylon control centre. A dull glow appeared deep within the barrel, growing bigger and brighter until it became blinding...
The End
(Battlestar Galactica/Warhammer 40,000)