The Umbral Knights played a role in the Indomitus Crusade under Lord Commander of the Imperium Roboute Guilliman's orders until they were tasked with staying behind after one of the initial conflicts of the Indomitus Crusade was won so that they could consolidate the Crusade's gains among the liberated worlds.
For ten millennia, Archmagos Dominus Belisarius Cawl has been working on a task set for him by the Primarch Roboute Guilliman before he was mortally wounded by the Daemon Primarch Fulgrim in the days after the Horus Heresy: a new legion of transhuman warriors. Developed on orders from Guilliman 100 standard centuries past, Primaris Space Marines were diligently developed and perfected by the Priesthood of Mars during the long intervening millennia.
As an optimist, but never a fool, Guilliman learned from the mistakes of the Horus Heresy, and he foresaw that the Forces of Chaos would never relent in their aim to bring the Imperium low. He anticipated that devastating times would once again engulf the galaxy and knew that warriors resilient enough to stand against them would be needed as never before. That time has surely come. Now, as the Imperium of Man is poised on the brink of annihilation at the hands of Chaos, his task is at last complete.
The Primaris Space Marine is a new breed of hero for this, the darkest age in the Imperium's history. These new warriors are the next step in the evolution of the Emperor's Angels of Death -- genetically altered from their brethren to be bigger, stronger and faster -- timely reinforcements for the Imperium's armies as their enemies close in for the kill in the wake of Abaddon the Despoiler's 13th Black Crusade and the birth of the Great Rift dividing the Imperium in two.
At the dawn of the Indomitus Crusade to retake the Imperium from the advancing armies of Chaos and xenos alike, Lord Commander of the Imperium Roboute Guilliman has gathered his new armada, along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood. They were not alone. Upon nearby Mars, Archmagos Dominus Belisarius Cawl had unlocked his vaults, producing from stasis the fruits of his longest labours -- the Ultima Founding. To complete the full deployment of his long-prepared masterworks would take months. Cawl's own fleet joined the Primarch, headed by his freighter-hulk, Zar-Quaesitor, a mech-ark class ship that carried within its massive hull a vast number of Primaris Marines still in stasis hibernation. The Archmagos brought with him several armies of Skitarii and Legio Cybernetica, alongside three lances of Questoris Knights from House Taranis.
As the Indomitus Crusade penetrated deeper into the galaxy, thousands of hibernating Primaris Space Marines -- some comprising entirely new Chapters and others designated as reinforcements for existing ones -- were awakened from their millennia-long slumber and made ready to join the fray. Many Chapter Masters welcomed their Primaris brethren into their ranks, accepting the new reinforcements gladly. Others, though, viewed these new creations with suspicion or outright hostility, claiming that the Emperor's work should never have been meddled with by mere mortals.
Despite cleaving a wide path through the darkness that beset the Imperium, the Indomitus Crusade began to break down. Once deployed, the new Chapters -- such as the Umbral Knights or the Rift Stalkers -- remained after the initial conflicts were won, seeking to consolidate the crusade's gains; in many cases, they did this by establishing their own new Chapter planets.
In this way, the Crusade not only freed worlds from the tyranny of the Dark Gods, but also strengthened their defences against further attacks that were sure to come. Later it was said that during the darkest hours the Imperium had endured since the Horus Heresy, it was the Indomitus Crusade that gave Mankind the hope to persevere.
The Umbral Knights' Chapter colours are currently unknown in Imperial records.
The Umbral Knights' Chapter badge is not currently listed in Imperial records.
- Codex Adeptus Astartes - Space Marines (8th Edition), pg. 21