Tenebra Uprising

The Tenebra Uprising was a joint-Imperial castigation campaign carried out by several Adeptus Astartes - including the Blades of the Lion, Death Templars, Imperius Ravagers and the Tempest Knights - to bring the wrath of the God-Emperor upon the rebellious secessionist forces of the Hēphaistos Coalition Technocracy, when they seized control of the Tenebra Sub-Sector and declared their independence from the Imperium. The Imperial forces were later joined by the then-unknown Shadow Talons Space Marine Chapter, who quickly made their presence felt by playing an instrumental role in breaking the stalemate between the opposing sides in the conflict.

Background
During the first century of the 33rd Millennium, the Tenebra Sub-Sector, located in the Caligari Sector, a vast, ancient and forgotten region on the fringes of the Segmentum Tempestus, falls into open rebellion. These sub-sector includes some of the oldest worlds in the sector, colonised by human as early as the Dark Age of Technology, while other were claimed by the early Imperium during the Great Crusade in the late 30th Millennium. Rick in ancient technology - such as unique xenos artifacts, carefully guarded and jealousy hoarded by the local sects of the Adeptus Mechanicus. Several of these forge worlds conspired together, forming the Hēphaistos Coalition Technocracy - a conglomeration of three forge worlds that came to a mutual agreement - a temporary partnership formed to achieve independence from the oppressive rule of the Imperium and strictures of the Crimson Accords. Having grown disenfranchised with Imperial rule and the strictures that forbade the highly independent Tenebrae Mechanicus factions from studying forbidden technology, several of these forge worlds had come to value their isolation and independence from Mars.

The Coalition declared their independence from the Imperium and began raiding various worlds of the sub-sector in order to obtain lost technologies they deemed too important, for mere humans, to have ownership or access to. Soon, scattered intelligence gathered by Imperial agents reached the ears of the High Lords of Terra, indicating that the Hēphaistos Coalition Magi had become increasingly corrupt, embracing forbidden technological blasphemies and dabbling in Silica Animus and the forbidden arts of Cybermancy. Some reports even claimed that they had begun to willingly make truck with debased renegades and consorting with vile xenos, trading for forbidden xenos artefacts and lore the Imperium could ill-afford to have fall into the hands of such hereteks.

In response, the High Lords of Terra called for a Crusade, to bring the wrath of the Emperor down upon those that would dare turn from righteous light. Several Adeptus Astartes Chapters, including the Death Templars, Blades of the Lion, Imperius Ravagers and the Tempest Knights, joined the large Imperial Crusade to bring the Tenebra Sub-Sector back into the Imperial fold. The conflict ensued over the next several decades, and threatened to tear apart the entire Caligari Sector. Soon, the death toll rose into the hundreds of millions, as several worlds were utterly devastated by the ceaseless warfare fought between the Imperial and Coalition forces. As the decades dragged on, several more worlds were drawn into the conflict, both for and against the Coalition's cause. By the end of the first century, both sides had been bled dry by the neverending conflict.

Slowly the secessionist forces had pushed back the Loyalist forces, inflicting a staggering number of casualties. Lacking the ability to end the conflict, the Imperial forces were forced to set up a blockade, to contain the threat of the Coalition forces. Sensing death, like carrion birds flying above a slowly dying creature, an ancient force of death-seeking predators slid out of the blackness of the outer void. Arriving without warning in 102.M33, the sudden appearance of the Shadow Talons' Chapter fleet caused alarm for both the Loyalist and Coalition forces operating within the Segmentum Pacificus. It was unknown if the unidentified Space Marine force had come to offer its aid to the Loyalist's or Coalition's cause. When both sides ran the ident checks of this mysterious Space Marine fleet, they identified this mysterious Chapter as the ' Umbra Unguis ', using the ancient High Gothic form of their name, or the ' Shadow Talons ' in Low Gothic. They had arrived in the war zone to draw blood. With the arrival of such deadly predators, this force would change the nature of the campaign. As suddenly as they arrived, the Shadow Talons fleet quickly slipped back into the void and disappeared. But their foreboding presence would be felt soon enough.

Not long after their unannounced arrival, the Shadow Talons officially entered the conflict during the Siege of Metis, one of the three forge worlds and primary instigators behind the Coalition alliance. The forge world was currently being attacked by the combined forces of both the Blades of the Lion and the Tempest Knights Chapters. However, they were locked in a bitter, long-running and highly protracted conflict with the forge world's primary forge-city of Coeus City, seat of the Metisian Mechanicus. The Shadow Talons' fleet then began a concussive bombardment directly above the previously unassailable sub-surface fortifications of the hive-capital, heedless of the collateral damage to the planet's population. The unrelenting bombardment caused massive tectonic force which shook the planet to its core, causing severe damage to the capital's infrastructure as well as several of the planet's cities.

The Shadow Talons then proceeded to launch a multi-vectored assault in full force, catching the Metis Skitarii forces unprepared and decimating a number of strategic points with their initial strike. A self-contained fleet-based Chapter, the Shadow Talons were operating fully-equipped and at peak strength. They fought as a single cohesive force that struck like a series of brutal thunder hammer blows. Into this hellish landscape the Shadow Talons launched a vanguard assault and descended deep into the bowels of the forge world's capital city. The unforgiving sons of Corax hacked and blasted their way into the interior of the beleaguered capital, and ruthlessly hacked down the Skitarii defenders. After hours of fighting, the Shadow Talons made their way towards the capital's titanic plasma reactors and planted melta charges amongst the delicate containment fields. They shadow killers then retreated as suddenly as they had struck, back into the upper levels to detonate the charges. Once back on the surface, the Shadow Talons put the frenzied tech-priests and Skitarii defenders to both bolter and blade.

The resulting destruction of Coeus City was significant, but it saw the swift collapse of the Metisian Mechanicus' resistance, and despite the damage sustained by the forge's factory-warrens, the envoys of loyalist Adeptus Mechanicus would be able to restart production with only minor delays. The Metisian Skitarii and Mechanicus bore the brunt of the assault's bloody cost, losing thousands, whereas the Shadow Talons only lost around one hundred Astartes. This cost, though high, was less than might have been expected from a drawn-out siege and the battle was lauded as a mighty victory for the advancing Imperial Crusade forces. It also established the reputation of the Shadow Talons as harbingers of death. Following the successful campaign on Metis, the Shadow Talons would continue to play an instrumental role during the rest of the Crusade. The campaign drug on for another six solar months, costing tens of thousands of lives on both sides, as the price for the Shadow Talons' need for brutal and bloody-handed retribution.