The Battle of the Alaxxes Nebula was an engagement that took place between the bulk of the Space Wolves fleet and the bulk of the Traitor Alpha Legion fleet within the vast, highly corrosive dust and hyrdrogen ice cloud fields of the Alaxxes Nebula in 007.M31, during the early years of the Horus Heresy. As the Space Wolves were still licking their wounds following their heavy losses during the Razing of Prospero, they are ambushed by a sizable Alpha Legion strike force and are subsequently routed at Yarant. Primarch Leman Russ organised a tactical retreat and fled towards the Alaxxes Nebula to seek temporary sanctuary. The Alpha Legion gives chase and soon the VIth Legion soon found themselves in a precarious predicament and were effectively cut-off and surrounded by the bulk of the Alpha Legion. Despite contacting the nearby White Scars fleet, who refused to assist the Space Wolves, Russ faced the prospect of imminent destruction, but by sheer dint of luck, or perhaps providence, the Space Wolves received help from an unexpected quarter -- from a contingent of Dark Angels hidden deep within the core of the nearly impassible clouds of the Alaxxes Nebula.
Following the Razing of Prospero, Leman Russ ordered his battered VIth Legion to muster within the Alaxxes Nebula. But unknown to the Wolf King, Horus had deployed the XXth Legion to launch a massive assault on Russ' battered and outnumbered Space Wolves. The Alpha Legion and its twin Primarchs, Alpharius Omegon, had long harboured deep grudges against the Space Wolves, and Russ in particular, for his criticism of their reliance upon trickery, manipulation and subterfuge to win battles rather than engaging in what the Space Wolves Primarch saw as honourable, open combat. The Alpha Legion relished the chance to prove their superiority against the arrogant Wolves of Fenris by delaying them long enough to keep them from contributing to the Imperial defence of Terra. Russ sent a distress call to the nearby White Scars, requesting that his brother Primarch Jaghatai Khan send his forces in order to assist the beleaguered VIth Legion against the traitorous Alpha Legion. Unsure as to which side the Space Wolves truly belonged, the Khagan sympathised with his brother Primarch's predicament, but refused to get involved until he was able to sort out the conflicting and often contradictory astropathic messages he had received. Until he knew, beyond a shadow of doubt, who was ally and who was an enemy, he refused to choose sides. Wishing his brother the best of luck, Jaghatai wished to seek his answers elsewhere.
Realising that VIth Legion faced a hopeless situation, Russ was demoralised and isolated himself within his personal chambers, forcing his First Captain Gunnar Gunnhilt, aboard the battleship Ragnorok, to assume command in his Primarch's absence. Ruminating upon the role the Emperor had forced upon him, Russ received counsel from Bjorn 'The One-Handed', a young Pack Leader in Tra (the Third Great Company) who had risen in much esteem since Prospero. He helped his Primarch come to terms with his past as the Emperor's 'Executioner', realising it had done nothing but brought ruin upon the Vlka Fenryka. Meanwhile, Gunnhilt led the Space Wolves fleet in a desperate breakout attempt or else be destroyed. Harried at every turn, the Space Wolves' fleet faced imminent destruction by the larger Alpha Legion fleet. Reinvigorated by the reemergence of the Wolf King, First Captain Gunnhilt and his crew sold their lives dearly in order to help slow the Alpha Legion advance, unfortunately the Alpha Legion fleet were still able to catch the limping Space Wolves fleet.
During the height of the ensuing battle, a large contingent of elite Cataphractii Terminators of Laernaean teleported aboard the bridge Russ's flagship, Hrafnkel, where the Wolf King seemingly battled Alpharius disguised as one of his own Laernaean Terminators. As the Alpha Legion were on the verge of ultimate victory, help arrived from an unexpected quarter, in the form of a large Dark Angels fleet led by a mobile Ramilies-class Starfort, the Chimaera, who had heard the Space Wolves' distress signals and determined that the VIth Legion were in fact still loyal to the Emperor. With the assistance of their Ist Legion cousins, the Space Wolves were able to force the Alpha Legion to withdraw.
In the battle's aftermath, the Wolf King and a contingent of his most trusted warriors sought audience with the Dark Angels' commander, Chapter Master Althalos, who was still ostensibly loyal to the Regent of Caliban, Luther. He informed the Primarch that his fleet had been despatched 59 years earlier, in 948.M30, before the outbreak of the Horus Heresy by the Regent, in order to conquer worlds and establish outposts. The Dark Angels hidden within the Alaxxes Nebula had been completely unaware of the eruption of the galaxy-wide rebellion or Luther's corruption back home on Caliban. At some point they had received fractures of information -- the Legions were now at war, the Istvaan III Atrocity -- but they had no clear view of who was now Loyalist or Traitor. Therefore, they chose to be cautious when approaching the Space Wolves before revealing themselves.
During the battle, one of their officers, Captain Ormand, had secretly infiltrated the Wolf King's flagship in order to determine if the Space Wolves were still loyal to the Emperor. His duplicity was discovered by Rune Priest Kva, who brought him before Russ. Seeing the Space Wolves valiantly battle the treacherous Alpha Legion, Ormand determined the VIth Legion were still loyal and informed his commander of their intent. They had then intervened on the Wolves' behalf and helped route the Traitor fleet. In exchange for men and matériel by the Dark Angels, the Wolf King gave a full accounting of the Warmaster's treachery and the view of the wider events that had, thus far, played out across the galaxy. Saddened by the news, Chapter Master Althalos decided to lead his forces back towards Caliban while Russ decided to set course for Terra, and the inevitable showdown with his treacherous brother, Horus.
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