Ultramarines - Indomitus Crusade: Near the end of the 41st Millennium the Imperium lay broken in two. The Great Rift, or Cicatrix Maledictum in High Gothic, had torn the galaxy asunder. The Emperor's realm was split by a seething belt of Warp storms that waxed and waned as they spewed armies of unholy Daemonic abominations into realspace in numbers previously undreamed of. Time itself distorted in the grip of impossible forces so that to read the linear progression of war across the galaxy became the toil of madmen and fools.Warp travel was more hazardous than it had ever been since the Age of Strife, leaving many thousands of Imperial worlds virtually isolated and forced to look to their own defence. The issues were even worse beyond the Great Rift in the Imperium Nihilus, where the light of the Astronomican was permanently reduced to the most distant and infrequent of glimmerings.Despite all of this, the Ultramarines did not falter in their defence of the Imperium. Their duty had always been the defence of not only Ultramar but of the whole of the Emperor's realm, and it was not one that they would shirk now.Many Imperial forces chose zeal and aggression over simply cowering behind their defences. Crusading fleets struck out into the void with fire in their hearts. Some won great victories, but the vast majority were engulfed by nightmarish phenomena and tides of malefic foes and were never seen again.There was one undertaking that overshadowed all others, however: the Indomitus Crusade. Launched from Terra and led by Roboute Guilliman, this vast military undertaking echoed the Great Crusade of old. Spearheaded by the newly founded Primaris Space Marines who fought beneath Guilliman's banner, and supported by the Adeptus Custodes, the Adepta Sororitas, the Sisters of Silence and vast battlegroups of the Astra Militarum and Navis Imperialis, the Indomitus Crusade fleets spread out from Terra to take the fight to the foe.With them they brought not only waves of Primaris Space Marine reinforcements for the embattled Chapters of the Adeptus Astartes scattered across the galaxy, but also the technology and Magos Biologis adepts required for each Space Marine Chapter to fashion their own new Primaris battle-brothers as the war raged on.Roboute Guilliman led one fleet of the many that comprised the crusade, Indomitus Crusade Fleet Primus, accompanied for much of the time by the mighty Zar-Quaesitor, Belisarius Cawl's Ark Mechanicus flagship within whose capacious holds thousands upon thousands of Primaris Marines slept in readiness for battle. Yet the Indomitus Crusade consisted of many fleets that travelled in short and perilous Warp jumps, spreading slowly out across the Segmentum Solar and then further, into the fringes of the Segmentum Tempestus, Segmentum Pacificus and Segmentum Obscurus.Ultramarines and Ultramarines successor forces both existing and new-founded accompanied many of these crusading fleets; some fought with them from Terra itself, either veterans of the Terran Crusade or Primaris Space Marines. Others were gathered up along the way, strike forces of Guilliman's gene-sons who had already been investing war zones across the galaxy when the Great Rift opened.Thus as the Indomitus Crusade pushed out ever further across war-torn Imperial space, the Ultramarines and their successors fought on many hundreds of disparate galactic battlefronts, against myriad terrible foes.