 To say that the galaxy is vast is an understatement to an almost ludicrous degree. The void is so immense that many simply cannot comprehend its scale as simple human frames of reference are, in the cosmic scheme, utterly minuscule. In due this enormitude strode the Emperor of Man, who declared it his intention to extend to all corners of space the arm of his Imperium. All students of Imperial history know that to do this he created his Primarchs, and from them the Legionnaires Astartes. The perfect soldier for an imperfect galaxy, the Astartes were the thundering hammer of the Great Crusade, transhuman genetic demigods designed to smash any and all foes that stood against them. Yet the Astartes could only be so many, and in only so many places at once. The galaxy is, after all, enormous, and the numbers amongst the legions never broke one million. While even a dozen Astartes could radically alter the course of a conquest, in many cases, numbers were called for. While the hallowed tales of the Great Crusade and the darker ones of the Horus Heresy ring loudest when referring to the victories and triumphs of the legions, far more plentiful by sheer numerical superiority, were the actions of unaugmented human troops. Know then that this is a record of the origins of the Exertus Imperialis, the Great Human Tide, the almost numberless forces of the Imperial Army. The first regiments of the Imperial Auxilia were formed on Terra during the fires of the Unification Wars. The Emperor, in those dark days simply another Terran warlord vying for control over the scarred wastelands of the homeworld, banded together the militaries of his first conquered kingdoms under his raptor and lightning banner. The warring Technobarbarian nations were as diverse as the history of Terra itself, and this extended to the strife epoch regiments, who were not, as some suppose they would be, formalized into one unified force, but rather valued for their differing styles of warfare and ideological temperaments. Some, particularly the most professional and stable formations, were selected by the Emperor himself for study and research purposes, submitting to simple genetic enhancement to bolster their fighting abilities. Early Geno regiments were esteemed for their ability to maintain a disciplined and, more importantly, genetically consistent fighting force in a planet beset by rampant mutation and atomic hurricanes. Regular foot troops were bulky stock bred for musculature and obedience, while the command cadres were formed of low-level psychers known as oxaurs, and augmented by field commanders imported from other regiments by sheer force of merit to be later woven in to future genetic selection processes. These techniques were said to have been admired by the Emperor, and certainly their genetic stability in testing mechanisms can be seen in the early attempts at fully augmented human soldiers, the Emperor's own thunder warriors. As unity spread across Terra, the Imperial army diversified with each new polity subsumed into the Emperor's banner. These regiments went through a turbulent period as the Imperium dusted off from the homeworld to stretch its grasp into the solar system. Some were granted the honor of serving alongside the burgeoning Astartes legions in the solar reclamation, adapting to the harsh void warfare the campaign entailed. Many more, however, were disposed of in accordance with their levels of unwillingness to adapt to both the Emperor's unified Terran regime or to the exigencies of the newly launched Great Crusade. What remained of the thousands of regiments that participated in the Unification wards became known as the Old Hundred, formed of the most loyal, the most adaptable, and most resilient of these regiments, which included, amongst others, one of the few surviving Geno regiments, the Geno-5-2 Chilliad, which would later make a dark name for itself serving alongside the 20th Legion, Alpha Legion, in the conquest of Nerth. With the Great Crusade beginning its first extra solar campaigns, the Emperor's reorganization of his unaugmented troops proved, as with all of his decisions, prescient and apt. The battlefields encountered by Imperial forces proved nothing like those of the techno-barbarian holds of old Earth, and, though the Legion as Astartes were more than capable of carrying the day whenever they were deployed, they could not be everywhere. Man was the greatest natural resource the Imperium could count upon in this age, and the newly formed Exertus Imperialis was there to provide it. Its size is by its nature uncountable, its structure almost unfathomable. Broadly speaking, it comprised under the umbrella of the Exertus, the Imperial Army, known as the Imperial Auxilia, the Armada Imperialis with its attendant warships and transports, and the core logistic, as well as, strictly speaking, the iterators of the Imperial truth and the loosely formed Remembrancer core, a diverse collection of writers, historians, poets, sculptors, painters and artists who accompanied Crusade forces to record their actions for posterity. Owing to this, the Exertus had nominal command over all non-Astartes military assets in the Imperium, including all regular ground troops, armor, artillery, aerial assets and void naval assets, as well as all attendant logisticians, munitore, medical staff, command cadres and intelligence staff, millions upon billions of humans, all operating in one mass, all toward one purpose. Officially, the Exertus and by extension the Imperial Auxilia were under command of the Officio Militaris upon Terra, but functionally were subservient to the exactors of true Imperial command in the field, the Astartes and their Primarchs, as well as, in almost all cases, the Mechanicum, the Titan legions, Night Houses, Rogue Traders Militant and even the Navigator Houses and Collegius Saicanna. All of these forces could, if they required or desired, command Imperial Army assets and manpower for whatever purpose was extant. While often the numerical bulk of an Imperial campaign, the Imperial Army were rarely, if ever, the independent actors in any given theater and were almost exclusively under the command of a higher authority from outside the structure of the Exertus Imperialis. With each new planet brought into compliance by the Imperium, a census and levy was taken, warranting that the planet paid its tithe to the furtherance of the Great Crusade and in doing so ensuring that the momentum of the Emperor's great endeavor did not falter. The humans brought into the fold this way varied in as many ways as there were planets in the Imperium, bringing unique and specialized fighting styles and organizational structures into the body of the Imperial Auxilia. Regiments varied in every way possible and the Army could count amongst it everything from highly professional fighting forces with millennia old histories on the planets they came from who had gladly joined the Imperial cause, unaltered, to entire battalions of enslaved penal troops from non-compliant or recalcitrant regimes. The clandestine Orta, for example, were composed of stormtroopers who relied upon stealth and surprise to carry the day, eschewing all armor support, while the Felizian 23rd Airborne relied on grav-shoot technology, including modified armored walkers for aerial drop operations. The Tanaghan Dragoons fought exclusively as mechanized infantry, while the Lucifer Blacks were so well trained and scarce they were primarily employed as bodyguards for expeditionary commanders. The names and variations go on and on. The Otramar, the Orante Drax, the Prosperine Spireguard, the Crescent-Sinned Sixth Torrent, the Therosian Vaultaguirs, Byzantianizars, Archite Palatines. The Honor rolls would cover a continent. Regimental size tended to vary. Some regiments were highly specialized, while others incredibly numerous. General historical consensus places the size of a regiment at what could be accommodated within a standard mass-hole transport conveyor, meaning the average size of an Imperial Army Regiment would approach 3,000 troops. The one regiment, one ship approach, was a logistical concession to the scale of the Great Crusade, removing the possibility of troops being left behind or accidentally double-billeted, but also in a coldly logical fashion ensured that in the event of naval losses, such as during an ambush upon a transport fleet, regiments were not fragmented amongst several different transports. The formation of regiments around common home worlds was a facet of the pragmatism of the Imperial Auxilia. The human worlds encountered in the Great Crusade had been cut off from the rest of humanity for many thousands of years. In most cases, the languages spoken were so far removed from Imperial Gothic as to be incomprehensible, and the cultural difference almost equally perplexing. Attempting to fold impressed troops into existing regiments that did not even share the same tongue as them was a recipe for disaster, and won the exertus sidestepped by simply raising and maintaining regiments using each individual world or system as their recruitment source. While this did mean supply lines for manpower intake were sometimes stretched ludicrously long, the momentum of the Great Crusade's conquest, as well as the combat losses a regiment could expect in a hotly contested war zone, meant that in most cases regiments were simply bled dry of men until they were no longer effective, only to be replaced by forces raised from freshly compliant worlds. Those that had adapted to Imperial culture well would be subsumed into other active regiments, while those that could not could best expect to be designated a specialized force, if their effectiveness had been proven, or at worst simply cannon fodder to be thrown at the enemy's guns to whittle down their ammunition reserves. The harshness of the Imperial Auxilia was a fact of life for billions upon billions of humans during the Great Crusade, and would only become worse for those inevitably caught in the fires of Horus's perfidy. Owing to their command structure, the loyalty or treachery of an Auxilia regiment was often not even theirs to decide, as they could simply be deployed by their Astartes or Mechanicum commanders to fight regardless of their own ideological convictions. In this manner, it is doubtless that many who fought on the side of the traitors were likely unwitting or hapless pawns in the game of Horus and his treacherous brothers, while similarly it is possible that some regiments who fought for the Emperor would have followed the warmaster, up and subsumed into the command of one loyal Primarch or another. In these dark times, as it was before, it is the role of the common Imperial soldier to simply obey orders, to live or to die by the whims of men greater than themselves, to be plucked from the world of their birth and herded onto an unknown battlefield, under an unfamiliar and indifferent sky. In remembering the countless tragedies of that dark time, let us never forget the uncounted billions who failed doing what they believed to be their duty, or who simply tried to survive in a world where their lives meant nothing.