The Grey Crusade

Though the conflict has gone by a different name in all other Imperial Records since its conclusion - the Failed Dynastic Foothold Campaign - the conflict is better known to those within the Chapter as The Obsidian STC. - a title earned because of what they discovered upon the surface of Amurtora.

History
The conflict had barely begun, and the former civilised world of Amurtora was one of the planets within the first star system they laid siege to. Amurtora was - judging from the ruins and other remains found upon its surface - once a civilised human world with technology levels at least matching that of the Imperium.

There was, however, no record of the world in Imperial archives. Whether that is because the world was never brought into the fold of the Imperium or because it fell from the Imperium's grasp along with any record with it is not known.

On the surface of the world, they discovered a structure that bore a striking resemblance to a manufactorum one might expect to see on the Forge Worlds of the Imperium. It was a truly massive structure, and - judging from the elements of the structure that had not been totally annihilated - its purpose was undeniably clear.

It had not been entirely destroyed with some of its structural elements deep beneath the ground being relatively intact, though from the outside it looked as if it were entirely in ruin. These relatively intact depths of the facility were only discovered as a result of members of the Chapter's 3rd Company being forced to retreat into and fortify a position within the ruins, the entry to the depths only being opened to the wider world as a result of the preceding fighting.

In the depths, they discovered one of the STC Machines which was lost during the awakening of the Tomb World. Its position indicated it was either in a position to be protected, studied or both. Where it was found seemed to indicated that whatever the reason for its presence in this part of the facility, it either wasn't being used to anywhere near its maximum potential, or it wasn't being used for its original purpose at all. Various other data fragments were also recover, with the systems that they were recovered from being found set up in the vicinity of the STC Machine.

In spite of the eventual loss and subsequent withdrawal from the planet before it was subject to an orbital bombardment, the Chapter managed to extract the STC Machine. and the gathered data. Knowledge of the recovery of the machine and the data slipped into obscurity, the Chapter sealing its lips tight. All that the Imperium at large know is that the Chapter tried and failed to penetrate into and establish their own foothold in the Sautekh Dynasty.

The Designs
The designs they found were interesting to say the least. The most interest data contained within the STC as well as data recovered from the secondary systems surround it within its pseudo-sarcophagus was the incomplete but not entirely useless data pertaining to two different but very similar patterns of Tactical Dreadnought Armour: The Aquilon Pattern and the Caterphractii Pattern. It also apparently designed with augmentation and extensive life support systems in mind, meaning it could theoretcally - should the designs ever be completed once again before being produced - function very similarly to the Dreadnought cybernetic combat walkers but with many of the benefits brought to the field by the Tactical Dreadnought Armour.

Based on the sightings of the Chapter - particularly by those rare few who have fought with them on the rarest occasions since The Obsidian STC conflict ended - they have not perfected any such suit of armour.

The other designs that the Chapter found most interested pertained to bionics - specifically larger scale bionics. Many of the designs spoke volumes of larger and stronger bionics that could also be easily interchanged. These designs were implemented by the Chapter, their Astartes becoming physically larger. Their forearms - or in some cases entire arms - were seen to have been interchanged with weapons such as elongated chainblades. Such designs are absent in the wider Imperium despite not being entirely dissimilar in regards to their basic concepts.