Ultramarines - War Disposition: Prior to the orders to assemble on Calth for the expected Ghaslakh Crusade, the majority of the XIII Legion had been distributed across the southern and eastern sectors of the galaxy in numerous crusade expeditionary fleets.Of these, Guilliman recalled fully twenty chapters to Calth, with fourteen of them rendezvousing at Saturn in the Sol System to take on supplies before making the onward voyage. This meant that somewhere in the region of 200,000 Legiones Astartes -- alongside uncounted mortal auxiliaries of the Imperial Army -- were deployed to Calth.Such was the death toll during the Battle of Calth, that while exact figures are impossible to obtain, it is estimated that no more than 40,000 Ultramarines were to escape Calth's system in the aftermath of the fighting, many of whom were casualties, with an indefinable number trapped beneath the surface of that ruined and radiation-wracked world engaged in the Underworld War.The Ultramarines recorded their casualties at the moment when Guilliman and the remains of the XIII Legion fleet departed Calth at 119,422 Legiones Astartes fallen in combat, with a further 28,392 rendered combat-incapable by battle injuries and trauma. Few of the Ultramarines chapters committed to Calth could muster even a quarter of their nominal strength after that campaign, and some were so decimated that they faced being reorganised into other chapters and their old designations removed from the XIII Legion's order of battle.Most of the injured were evacuated to the surviving voidcraft of the Legion fleet and swiftly returned to combat duties in the crisis that was unfolding across Ultramar, a crisis that forced Guilliman to order the prioritisation of military assets over the stranded civilians of Calth in the brief evacuation effort. Almost 40,000 Ultramarines, both wounded and combat-ready, were forced to remain on Calth, some as volunteers, set to the protection of those civilians who could not be evacuated, and others due to the brutal dictates of circumstance.Of the forces of the Excertus Imperialis, the Imperial Army, details are more vague, but it seems likely that at least half a million men-under-arms perished during the fighting, alongside the entire fighting complement of the Legio Praesagius.Of those Ultramarines chapters that were not recalled for the Ghaslakh Crusade, the following details are known: The 7th Chapter was embarked on a costly campaign sweeping the Eastern Fringe of a splintered Khrave infestation that threatened to overwhelm Imperial colonies established in the region and could not be spared for the muster, while the 10th Chapter was scattered across the north-eastern limits of Imperial expansion and was simply too far away to have been considered for recall.The 24th and 25th Chapters, elements of the Evocatii, alongside the 19th Chapter, were dispersed across the most important worlds of Ultramar to remain as Guilliman led the bulk of his Legion to war, unaware of the coming storm that was to follow, but spared at least initially from its ravages.Alongside a great many bonded voidships of the Imperialis Armada, and hundreds of military and Mechanicum transport vessels, the bulk of the Ultramarines fleet was at Calth for the muster, and caught ill-prepared for the Traitors' attack and suffered savagely for it.Many of the Ultramarines capital and cruiser class voidcraft were hammered into burning hulks, were simply missing or were sorely damaged and in need of repair. This state of affairs left the Legion, and Ultramar, dependent primarily on smaller voidcraft for their defence and strategic transport, and military ship-building became a priority for those worlds which were left able to do so.Guilliman sought to improve his position by adding to his few remaining heavy warships (a handful had not been present at the muster and so were spared the ambush), with additional warships appropriated from the Imperialis Armada if they were available and modified for Space Marine use. Where possible Guilliman made capturing enemy warships by boarding action a priority. The rapidity and efficiency with which this was done was nothing short of phenomenal and would have great import on the battles of the Horus Heresy to come.