Tiberian Meteors

The Tiberian Meteors
Once proud servants of the people of Tiberia V, the Meteors were raised up initially as a defense and policing force limited to their homeworld.  As the Great Crusade churned onwards, however, it became clear that the intense urban pacification doctrine the Meteors were subjected to was hardly necessary on their largely compliant home planet, and would be better put to use in the wake of the Astartes, especially as a supplement to the witch hunting Justicars.  The prospect of serving their primarch more directly resounded in the hearts of a great many Tiberians, swelling the ranks of what had been a limited force to the size of respectable regiment.
After an initially disastrous effort to quash an entrenched cultist presence in a hive world, the Meteors reorganized and supplemented their urban policing training with anti-psyker tactics, a change that would garner enough victories against violent covens to draw the attention of the Justicars.  What followed was a tight arrangement in which Justicar commandos were lent to the Meteors as instructors, and the Meteors were molded into a unit of brutally efficient urban shock troops with a penchant for killing witches.  Trimmed down for effectiveness, the Meteors settled at about one thousand soldiers, each thoroughly trained in rapid insertion, urban combat, dealing with psykers, and remaining as long as necessary to clean up after the occult and train local forces to prevent further incursions.
After accumulating an impressive array of successes, the Heresy would only bring confusion and pain.  Blind to the subtle shifts in the training regimens provided by the Justicar commandos, it was all too late when the Meteors realized that their mentors had fallen to Tzeentchian influence.  The treachery only became obvious when Uriel himself directed the Meteors to conduct a salted earth operation on the capital city of an agri-world that was supposedly under the influence of a powerful psyker that had seized the governor’s position.  Following orders to the letter, the Meteors thundered down on the city from the stars and conducted a bloody purge of the planetary government.  The local PDF, though slow to react, responded with a futile siege as their waves of inexperienced militia crashed and broke against the hardened ranks of the Meteors.
Only after a day and night of massacre was the deception revealed, as a Justicar courier informed the Meteors’ command that there was no psyker threat to begin with, that the Meteors had just destabilized a loyal Imperial world.  The commanders were furious, but as they surveyed the great swaths of corpses left in the wake of their assault, the awful truth set in – there would be no chance to explain, and certainly no mercy.  As an all-consuming dread swelled to fill the ranks of the Meteors, the Justicar courier presented the second half of his message: Swear loyalty to the Justicars and be spared.
The Meteors retreated to space, insisting that they needed to discuss the Justicar’s proposition as a regiment.  Coming to an understanding that they could not return to the Imperium after their crimes, the general consensus was to join the Justicars, though a handful opted to resign their positions and submit to Imperial justice.  For the duration of the Heresy, the Meteors were assigned to the task of disrupting the operations of the Eyes of the Emperor, as well as hunting sanctioned psyker brigades within other regiments of the Imperial Army.  Though they fought to avoid aligning with the Chaos gods, Tzeentch worked his way into the Meteors’ ranks, and it became increasingly common for recruits to be chosen from the warp-sensitive.  The Meteors’ combat doctrine was unchanged, however – only supplemented by the growing number of psykers within the regiment.
Following the Heresy and the devastation of Tiberia V, the Meteors continued to act as auxiliary to the Justicars, wreaking havoc on Imperial infrastructure and terrorizing supply lines for decades to come.