Drop Site Massacre

The Drop Site Massacre of Istvaan V was one of the major turning points that occurred during the great galactic civil war that engulfed the Imperium of Man in the early 31st Millennium known as the Horus Heresy. During the massacre three Loyalist Space Marine Legions -- the Iron Hands, the Salamanders and the Raven Guard -- were betrayed by 4 other Legions they believed were loyal to the Emperor of Mankind, but in fact had already betrayed the Imperium and turned to the service of the rebellious Warmaster Horus and Chaos.

History
In response to Horus' betrayal of the Loyalist Astartes in the Sons of Horus, Emperor's Children, World Eaters and Death Guard Legions at Istvaan III, the Primarch of the Imperial Fists Legion, Rogal Dorn, on the direction of the Emperor who had learned of Horus' actions from the Loyalist survivors aboard the Eisenstein, ordered 7 Loyalist Space Marine Legions to Horus' base on the world of Istvaan V to challenge the Warmaster. They would attack in two waves and fall under the supreme command of the Iron Hands' Primarch Ferrus Manus. The Legions comprising the first wave were the Iron Hands, Salamanders, and Raven Guard. The Legions comprising the second wave were the Alpha Legion, Night Lords, Iron Warriors, and a large contingent of Word Bearers that their Primarch Lorgar had stationed in the star system. Unknown to Dorn and Ferrus Manus, the Night Lords, Alpha Legion, Iron Warriors and Word Bearers had all turned from their service to the Emperor and pledged their loyalty to Horus, and been instructed to keep their new allegiance to Chaos a secret.

The Iron Hands, Salamanders and Raven Guard were deployed in the first wave of the assault. After they secured the drop site, they were to have been followed by the arrival of the other four Legions. The first wave secured the drop site at heavy cost. Horus ordered his front line troops to fall back, tempting Ferrus Manus to overstretch his already thin lines. Against the advice of Corax and Vulkan, Manus led his Veterans against the fleeing Traitor Marines unsupported. Manus then brought his brother Fulgrim to combat. As the two Primarchs drew their weapons, the Raven Guard and Salamanders fell back to regroup and allow the second wave's Legions to advance and earn glory. However, as they returned they were mowed down by the four Traitor Legions that had landed to supposedly support them, thus revealing their new allegiance to Chaos. Horus then pressed his own attack and sandwiched the Loyalists between the two Traitor forces, killing most of them. Several determined groups of Loyalist Space Marines managed to break out of the trap and escape back to the few remaining Loyalist drop ships.

Dropsite Massacre
Taking stock of their dire situation, Primarchs Corax and Vulkan conversed on what the proper course of action should be, but soon found themselves arguing over which way to proceed. The Salamander's Primarch suggested that they attempt to make a tactical withdrawal to their respective dropships and dig in to resist and further attacks. While Corax advocated that they should do whatever they could to make good their escape from the slaughter. Neither primarch could agree with the other, therefore, Corax turned from his fellow brother primarch and ordered his legion to retreat. A short while later, the two primarchs received a direct artillery strike upon their position. By the grace of the Emperor, Corax somehow managed to survive, but as to the fate of his brother Vulkan, nothing was known.

In the meantime, the second-wave, composed entirely of Traitor Legions turned upon their former allies and began to slaughter them in earnest. The Iron Hands were apparently slaughtered to man. During the midst of this brutal carnage two primarchs from opposing sides confronted one another in a final showdown. Fulgrim of the Emperor's Children and Ferrus Manus, once as close as true brothers, fought a bitterly contested, titanic struggle. Ferrus Manus lost and was beheaded by his former brother, Fulgrim during their dual. Fulgrim was soon beset by grief as he stared down at his once beloved brother's headless body; in this moment of weakness as the Emperor's Children Primarch repudiated his allegiance to Chaos, the Greater Daemon of Slaanesh within his potent blade tricked him into lowering his mental shields, and possessed him, crushing Fulgrim's soul into the recesses of his mind - a mute witness to the daemon's actions. The daemon would later present Ferrus Manus' head to a delighted Horus.

On the other end of the battlefield, the Raven Guard were confronted by the treacherous Word Bearers, with their Primarch Lorgar, Kor Phaeron and Erebus at its vanguard. The two Legions fought one another in bitter combat. In the midst of this battle, the Word Bearers unleashed the elite unit known as the Gal Vorbak - Astartes whom allowed themselves to be possessed by daemons. They attacked the Raven Guard's Primarch enmasse, but despite the advantage of numbers, Corax's formidable abilities as a consummate warrior proved to be more than a match for the possessed Astartes, slaying them with impunity. Seeing the slaughter of his most favoured sons, Word Bearer's Primarch Lorgar attempted to intervene, preventing the death of several Gal Vorbak Astartes. The two opposing primarchs then dueled one another in close combat, the Raven Guard's Primarch quickly gaining the upper hand over his outmatched brother. Lorgar had always been more of a scholar than a warrior, which proved to be his downfall, as Corax prepared to execute him. Lorgar was spared from execution by the intervention of the Night Lord's Primarch, Konrad Curze at the last moment. The Night Haunter and the Raven fought a brutal close combat battle. Curze quickly gained the upper hand over his battle weary brother and prepared to slay him, but Corax just barely managed to escape by taking to the sky with his master-crafted Jump pack.

The outnumbered Loyalists were surrounded and brutally butchered. Refusing the acquiesce, the remaining Raven Guard and Salamanders Legions stubbornly defended themselves, trying to hold off the inevitable slaughter for as long as possible. Though they suffered an atrocious number of casualties, the Loyalists managed to hold their own, until the Primarchs Mortarion of the Death Guard and Angron of the World Eaters joined the fray. Bolster by the support of the infamous Emperor-class Titan Dies Irae the Traitors killed tens of thousands of Loyalist Astartes. At the height of the massacre the Warmaster Horus entered the fray, at the head of his elite Terminators known as the Justaerin, slaughtering the Loyalists in wrathful anger.

Any hope for escape for the Loyalists was quickly crushed when the traitorous Iron Warriors destroyed the first wave's dropships. The Loyalist ships that orbited the embattled planet were also mostly annihilated by the vastly superior numbers of the Traitor's fleet. Despite the odds arrayed against them, some of the Loyalists on the ground, managed to survive against these untenable odds - miraculously escaping through the tightening cordon of Traitors that surrounded their position. The Raven Guard fared better than their brother Legion, the Salamanders in escaping the brutal massacre. But the Salamanders at least managed to save a few surviving Astartes from the decimated Iron Hands Legion away from the slaughter. Imperial history does not record the fate of these surviving Salamanders or their missing Primarch Vulkan. The Raven Guard's Primarch just barely managed to board a fleeing Thunderhawk gunship to make good his escape, but was thwarted in the attempt when it was shot down almost immediately by the gunfire of the Traitors. The badly damaged ship crashed on the outskirts of the Urgall Plateau.

Raven's Flight
Surviving the crash, Corax quickly regrouped the remaining warriors of his Legion, and learned much to his shock and consternation that a large percentage of his Legion had been utterly annihilated during the ensuing slaughter. They took to the highlands of the surrounding hills and took to the shadows, hiding from their relentless pursuers. During their flight, their position was nearly discovered from a roving armour column of traitorous Iron Warriors, but they were destroyed in a Raven Guard ambush and wiped out.

Thirty days after the initial planetary assault the future looked grim for the fleeing survivors. They had no word from either the surviving Iron Hands or Salamanders Legions. The Primarch ordered his warriors to dig-in and hold position at Lurgan Ridge while he undertook a lone reconnaissance of their original drop site to determine their options. Utilising his innate psi-abilities to escape detection, Corax successfully conducted a reconnaissance of the Traitor's positions around the heavily fortified drop site. Though the Primarch informed his men that his mission was to reconnoiter the drop site, his primary objective was to scour the Urgall Plateau for the bodies of his fallen sons, but he failed to find them.

After ninety-eight days of relentless pursuit, the Raven Guard survivors were finally backed into a literal corner. Caught upon the windswept mountainside Corax's Legion remained resolute. Behind the peak stretched great salt plains that had forced them into this last, defiant stand. Ahead of them massed the might of the World Eaters, the rage-driven Legion of Angron, who strode at their head roaring for the blood of his brother primarch. A sea of white and blue spattered with the red of gore swept up from the valley intent on the destruction of the Raven Guard. Maddened by neural implants and driven into a battle-frenzy by inhuman cocktails of stimulants, the berserk warriors of the World Eaters pounded up the sloping mountainside while their tanks and guns provided covering fire; every warrior bellowed his eagerness to fulfill the blood oaths he had sworn to his primarch.

But before they could utterly eradicate the surviving Raven Guard, the World Eaters were attacked by an unexpected quarter. Broad-winged aircraft plunged down from the scattering of clouds, missile pods rippling with fire. A swathe of detonations cut through the ranks of the World Eaters, ripping through their advance companies. Incendiary bombs blossomed in the heart of the approaching army, scattering white-hot promethium over the steep slopes. Corax looked on with incredulity as blistering pulses of plasma descended from orbit, cutting great gouges into Angron’s Legion.

The roar of jets became deafening as drop-ships descended on pillars of fire: black drop-ships emblazoned with the sigil of the Raven Guard. The legionaries scattered to give the landing craft space to make planetfall. As soon as their thick hydraulic legs touched the ground, ramps whined down and boarding gateways opened. At first the Raven Guard were in stunned disbelief. A few shouted warnings, believing the drop-ships to be enemy craft painted to deceive. But these dropships were part of a desperate rescue mission devised by Commander Branne, a Raven Guard Captain that had been left in charge of the Legion’s homeworld of Deliverance. Without further delay the Raven Guard survivors quickly marshaled for embarkation and escaped aboard the dropships, breaking for orbit and leaving behind the frothing berserkers of the World Eaters, their angry primarch baying for their blood.

Aftermath
Barely a handful of Loyalist Space Marines escaped with their lives from Istvaan V to bring word of the further betrayal of four more Astartes Legions to the Emperor. A critically wounded Corax was brought back to Terra in a stasis tube. Vulkan was missing, presumed dead, though he would later reemerge after a harrowing journey back to Terra to lead his Legion once more. Vulkan was 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 and the end of the Horus Heresy.