First Battle for Balten IX

The First Battle for Balten IX was a major battle that occurred between the Heirs of Lupercal Chaos Warband during an excursion out of the Maelstrom into the Segmentum Obscurus. But during their sojourn towards the western part of the galaxy, they encountered a large joint-Imperial task force comprised of multiple Space Marine Chapters, including the Will Breakers, Jade Knives and the Feral Sons.

History
On an excursion outside the Maelstrom into the Segmentum Obscurus, the Heirs of Lupercal attacked the Imperial world of Balten IX, having identified as ripe for plunder and slaughter. But the Heirs did not count on coming into contact with several Adeptus Astartes chapters, in particular the Will Breakers, Jade Knives, and Feral Sons Chapters. These three Chapter were busy carrying out their duties during the Indomitus Crusade, against the various enemies of Mankind that were assailing the Imperium all sides. This was due to the recent formation of the massive galaxy-spanning tear in reality, known as the Cicatrix Maledictum, following the destruction of the fortress world of Cadia during the Thirteenth Black Crusade.

Their reputation having preceded them, these Loyalist Chapters knew they had an opportunity to finally remove a vile threat to the wider Imperium. A massive void battle occurred both in orbit above Balten IX and on the surface. The large warband caused as much destruction and slaughter as possible, targeting lightly defended cities and smaller towns, massacring thousands of innocent civilians. But in the end, the combined force of Loyalist Chapters threatened to overwhelm and destroy the Heirs. Sensing their imminent defeat, the Heirs hastily withdrew from the surface of the planet, but in one last act of spite, they launched a deadly salvo of cyclonic torpedoes into the atmosphere that contained the deadly life-eater virus. Billions of innocents lost their lives. The Heirs managed to break the Imperial blockade and fled into the Warp, for parts unknown.