The campaign concluded successfully for the White Scars in 007.M31, during the early years of the Horus Heresy.
But the unexpected intervention of the Alpha Legion at Chondax during the void battle that became known as the "Chondax Engagement" resulted in the White Scars Legion both learning of the Warmaster Horus' rebellion against the Emperor of Mankind and making the decision to ultimately return to Terra to aid the Loyalists in its defence.
The Cleansing of Chondax
Shortly after the Triumph of Ullanor, the Primarch Jaghatai Khan and his Vth Legion were next sent to the worlds of the trinary Chondax System. The triple star system was comprised of the planets Epihelikon, Teras, Chondax, Honderal, Laerteax and Phemus IV, the furthest of the outlying worlds.
The culmination of this campaign took place upon the Dead World of Chondax, labeled Chondax Primus EX5, 776 NC-X-S by Imperial cartographers, but named the "White World" by the White Scars due to its salt-encrusted earth which slowly absorbed all moisture on the surface, leaving the world largely barren, though the terrain reminded some of the White Scars of their own Legion homeworld of Chogoris.
The White World was the crucible of the whole campaign, the nexus of those Greenskin forces that had chosen to go to ground in the star system after their defeat on Ullanor Prime. The Great Khan was ordered by the newly-promoted Warmaster Horus to hunt the remnants of the Ork Empire destroyed during the Ullanor Crusade, the last slivers of the Overlord Urlakk Urruk's Greenskins.
The brutal campaign lasted six long Terran years as the White Scars hunted the remaining Greenskin forces to extinction on Chondax and across the length and breadth of the trinary system.
It was at Chondax that the White Scars would first learn of the outbreak of the Horus Heresy and the betrayal of Horus Lupercal when they received urgent astropathic messages from Rogal Dorn, the Primarch of the Imperial Fists Legion, who had been named the Praetorian of Terra, the commander of the Throneworld's defences. Dorn explained that Horus and eight other Primarchs and their Legiones Astartes had turned upon the Emperor and initiated civil war. He requested that the White Scars immediately return to Terra to aid in its defence from the expected Traitor assault.
It was then that the White Scars discovered their route out of the Chondax System blockaded by the unexpected arrival of a portion of the fleet of the Alpha Legion, a brother Space Marine Legion whose loyalty in the new conflict was unknown to Jaghatai Khan. The White Scars found themselves hemmed in and unable to maneuver for Warp translation by a task force commanded by the Alpha Legion Primarch Omegon who was under orders from Horus to peacefully offer the White Scars an opportunity to join the Traitor cause.
However, instead of opening communications, the Alpha Legion fleet moved to attack, holding back its Battleships and Cruisers but allowing its Escort vessels to assault the White Scars fleet unprotected by the larger capital ships, leading to heavy losses.
The Great Khan, leading the defence of his fleet from the command throne of his flagship Swordstorm, found the Alpha Legion's action completely baffling but took advantage of the disarray to skillfully execute a fleet formation known as "The Chisel" which smashed a wedge in the Alpha Legion fleet and allowed the White Scars' fleet to escape into the Warp to begin the long jounrey back to Terra in search of answers for what was ripping the Imperium apart.
Having received conflicting accounts of who had betrayed the Emperor in his orders from Horus and a transmission with his great friend Leman Russ, the Primarch of the Space Wolves Legion whose fleet now faced the bulk of the Alpha Legion fleet, the White Scars fleet first set course for Prospero. The Khan was determined to discover the truth of this mayhem for himself and the first stop was the homeworld of Magnus the Red, whose Thousand Sons Legion Leman Russ claimed to have assaulted on the orders of the Emperor after they had violated the Edicts of Nikaea.
Faced with the dilemma of aiding the weakened Space Wolves against a powerful force of Alpha Legion attackers, or returning to Terra as ordered by Rogal Dorn, Jaghatai Khan first chose to go to Prospero to seek out the truth of the who had betrayed the Emperor for himself. Satisfied at what he found there during what became known as the Second Battle of Prospero, the Great Khan eventually did his duty and made the long journey back to Terra to aid in its defence.
Later, the Primarch Mortarion of the Death Guard Traitor Legion would remark that that something foul had taken place at Chondax, as Horus' original orders for the Alpha Legion were to recruit the White Scars to the Traitor cause. Instead, under orders either from Alpharius or Omegon, they had unleashed an unexpected and ineffectual attack, avoided any attempt at communication with the White Scars, and kept the White Scars occupied until they could receive a message from Rogal Dorn warning them that Horus and his allies had turned upon the Emperor.
Indeed, the only reason this message had even been deliverable through the Warp in the Chondax region of space was because Omegon had dispatched an Effrit Stealth Squad to destroy a Cadian Pylon-type xenos construct located at Tenebrae 9-50, an asteroid facility garrisoned by the Alpha Legion that was blocking astropathic communications from Terra. It seemed that the Alpha Legion, or at least elements within it, had wished for the White Scars to remain true to the Emperor and join the Loyalist cause.
- Brotherhood of the Storm (Novella) by Chris Wraight
- The Primarchs (Anthology) edited by Christian Dunn, "The Serpent Beneath" by Rob Sanders
- Scars (Novel) by Chris Wraight
- The Horus Heresy Book Eight - Malevolence (Forge World Series) by Neil Wylie and Anuj Malhotra, pp. 75-105