Drop Site Massacre - Aftermath: Barely a handful of Loyalist Space Marines escaped with their lives from Istvaan V to bring dreadful word of the further betrayal of four more Space Marine Legions to the Emperor. A critically wounded Corax made the dangerous journey through the Immaterium back to Terra, arriving 133 solar days after departing the Istvaan System and finally reaching the Sol System -- the heart of the Imperium -- to seek audience with the Emperor.Vulkan was missing and presumed dead for long solar months, though he would later reemerge after a harrowing journey back to Terra himself, to lead his Legion once more. After the conclusion of the Horus Heresy, Vulkan would be one of the Primarchs who protested Roboute Guilliman's publication of the Codex Astartes and the splitting of the remaining Space Marine Legions into 1,000-man Chapters following the death of Horus. The Salamanders, along with the Iron Hands and the Raven Guard remembered as the Shattered Legions, would spend the remainder of the Horus Heresy rebuilding their decimated Legions and were too weakened to play any further role in the great conflict.In the days after the battle, the Traitor Legions salvaged a large number of vehicles, wargear and other war materiel from what the Loyalist Legions had left on the field. This salvage was repaired and modified for the Traitor Legions' use and then put back into frontline service to be used against the Imperium. Some of this equipment would still be in service with certain Chaos Space Marine warbands in the late 41st Millennium.Orbital space around Istvaan V was busy as the vessels of 8 Legions assumed formation prior to transit to the system's Mandeville jump point. Over 3,000 vessels jostled for position above the darkened fifth planet, their holds bursting with warriors sworn to the service of Horus. Tanks and monstrous war machines had been lifted from the planet with incredible efficiency and an armada greater than any in the history of the Great Crusade assembled to take the fire of war into the very heart of the Imperium.Following the victory of the Drop Site Massacre, Horus called a meeting of the Primarchs of all 8 of the Traitor Legions aboard his flagship, the Vengeful Spirit. Five of the Primarchs, including four who had fought at Istvaan V, met in person, including Horus, Fulgrim, Angron, Mortarion and Lorgar. Three appeared through the use of hololithic emitters that transmitted their signals through the Warp, including Perturabo, Night Haunter and Magnus the Red, who had only recently joined the Traitors after the Scouring of Prospero when the broken remains of his XV Legion had been transported by Tzeentch into the Eye of Terror to the Planet of the Sorcerers.The Thousand Sons, bitter at what they perceived as their betrayal by the Emperor, now willingly became the eighth Traitor Legion. The council of Traitor Primarchs made their plans for the next step in their war against the Emperor and then each Legion went its way according to its assigned role.Unbeknownst to the surviving Raven Guard, Alpha Legion operatives had secretly infiltrated their ranks during the Drop Site Massacre, surgically altering their own operatives to resemble dead Raven Guard Legionaries and then inserting them into Corax's Legion during the chaos of their flight following the slaughter in the Urgall Depression.Alpharius Omegon had been told by the secret alien organisation known as the Cabal that the XIXth Legion was going to receive in the future an extremely valuable, top-secret Imperial asset that would be of great use to the cause of Horus. Impersonating Horus, the Alpha Legion Primarchs ordered a pursuing World Eaters fleet to stop all action against Branne's fleeing ships, so that the Raven Guard would survive the slaughter on Istvaan V and come into possession of the asset, which the Alpha Legion's infiltrators could then steal.The fleets of Angron, Fulgrim, Mortarion, Lorgar and Horus' own Legion would rendezvous at Mars, now that word had come from the Tech-priest Regulus, the Mechanicum's liasion with the 63rd Expeditionary Fleet, of that planet's fall to Horus' supporters within the Dark Mechanicum during the internecine conflict known as the Schism of Mars. With the manufacturing facilities of Mondus Gamma and Mondus Occullum wrested from the control of the Emperor's forces, the forges of Mars were free to supply the Warmaster's army.The eager warriors of the Alpha Legion were singled out by Horus for a vital mission, one upon which the success of the entire venture could depend. Following Horus' manipulation of Leman Russ into assaulting the homeworld of the Thousand Sons, the Space Wolves were known to be operating in the region of Prospero. In the nearby system of Chondax, the White Scars of Jaghatai Khan were sure to have received word of Horus' rebellion and would no doubt attempt to link up with the Space Wolves. Horus could not allow such a grave threat to appear, and so the warriors of Alpharius were to seek out and attack these Legions before they could join forces.The Night Haunter's fleet had already departed, bound for the planet of Tsagualsa, a remote world in the Eastern Fringe that lay shrouded in the shadow of a great asteroid belt. From there, the Night Lords' terror troops would begin a campaign of genocide against the Imperial strongholds of Heroldar and Thramas, star systems that, if not taken, would leave the flanks of the Warmaster's strike on Terra vulnerable to attack. The Thramas System was of particular importance, as it comprised a number of Mechanicum Forge Worlds whose loyalty was still to the Emperor.The ships of the Iron Warriors prepared to make the journey to the Phall System where a large fleet of Imperial Fists vessels were known to be regrouping after a failed attempt to reach Istvaan V in time to join the Loyalist assault. Though Rogal Dorn's warriors had played no part in the Drop Site Massacre, Horus could not allow such a powerful force to remain unmolested.The enmity between bitter Perturabo and proud Dorn was well known, and it was with great relish that the Iron Warriors set off to do battle with their old rivals. With his flanks covered and the Space Marine forces that could potentially reinforce the heart of the Imperium soon to be embroiled in war, the Traitors were ready to unleash 9 Terran years of devastating civil war upon the Imperium in the name of Horus and the Dark Gods.