Dark Angels - Chapter Organisation: Following the tragic events of the Horus Heresy, the Dark Angels began acting suspiciously and growing more insular, which was noted by many watchful eyes. Having incorporated the structure of the original Order on Caliban into the Legion, the remaining Dark Angels took that knightly brotherhood a step further, becoming even more monastic in manner.The Dark Angels sought to lay down the new rigours that would govern them in the wake of the terrible events that had led to the Fall of Caliban. At this time in the early 31st Millennium, entire new divisions of the Imperium, such as the Inquisition, were developed with the sole purpose of seeking out and destroying internal corruption related to the treachery of the Horus Heresy and the actions of Chaos on the Human-settled worlds of the Imperium.Inspections following the destruction of Caliban judged the Dark Angels fit to continue as a Loyalist Legion. Some leeway for their new reclusive behaviour was granted due to the simultaneous loss of the Legion's primarch and homeworld, but largely it was allowed because of the Dark Angels' ongoing and relentless heroics against the Imperium's foes during the travails of the Great Scouring.Regardless of these allowances, the Dark Angels remained closely monitored by the Imperial authorities and particularly by the nascent Inquisition. After the disappearance of their primarch, it did not seem that strange for the remaining Dark Angels to withdraw further into their own brotherhood. If before they had been described as reserved, now they were, at best, taciturn: at worst, they were cold and austere.Behaviour that once would have been described as pensive was now more like a brooding silence. Yet there was one thing that had not changed -- their campaigns continued to be well-planned and effective actions. If the Dark Angels were in some strange mourning, it in no way dampened their ability to bring battle to the enemies of the Imperium and of Mankind.Many changes happened within the Imperium during those dark days. Although Horus had been defeated at the Siege of Terra and his remaining Traitor Legions driven into the Eye of Terror, the High Lords of Terra and the remaining Loyalist primarchs still dreaded the resurgence of Chaos. They had all recoiled in horror at the full realisation of how insidious the betrayal had been, how far across the galaxy the roots of corruption had spread. Never again could the Imperium be subjected to such widespread rebellion; drastic measures had to be undertaken.To avoid the threat of the Space Marine Legions falling under the influence of the Archenemy, the remaining Legions were sub-divided into a number of smaller Chapters. Under the new structure of this so-called Second Founding, each Chapter's size was limited to a thousand warriors. The organisation, tactics and roles of these new "Chapters" -- a word derived from the former primary sub-divison of a full Legion under the strictures of the Principia Belicosa -- were defined in a hugely influential work known as the Codex Astartes.Roboute Guilliman, the primarch of the Ultramarines who had become the Lord Commander of the Imperium and the Imperial Regent in the wake of Malcador the Sigillite's death and the Emperor's internment in the Golden Throne, almost single-handedly undertook the work of preparing the Codex Astartes. The proscriptions within its pages not only lessened the risks of a single Traitor altering the course of the Imperium, but also allowed the limited number of Loyalist Space Marines remaining to be more flexible -- spreading more widely across the galaxy to confront Mankind's many enemies.The organisation of the Dark Angels Chapter and its Unforgiven successors differs from the standards of the Codex Astartes in the shape of its higher ranks, along with the order of battle of its 1st and 2nd Companies, which were the only survivors of the wings of the Hexagrammaton.