Planet Killer - 13th Black Crusade: As the end of the 41st Millennium drew closer, the dire portents indicated that Abaddon's long-feared 13th Black Crusade was imminent, as a pattern emerged in the Chaos attacks launched into Imperial space in the sectors surrounding the Eye of Terror in 999.M41.Deep within the anarchy of this hell-region of the Immaterium, ancient feuds had been set aside in the face of Abaddon's leadership as the Warmaster of Chaos.Bitter hatreds were quelled and even Traitor Legions with a deep-seated hatred for one another shared an uneasy peace so that they might launch the greatest coordinated assault upon the Imperium in the Long War since the time of Horus.Binding oaths and debts had been called to account and a force, the likes of which had not been seen since the Horus Heresy, had been assembled, ready to strike the Imperium like a thunderbolt.As part of their constant vigil around the Eye of Terror, highly trained units of Cadian Kasrkin were pushed into the swirling maelstrom, desperate to find some indication of where the first blow would land. Astropathic divination pointed towards the blighted world of Urthwart, a world already taken by Chaos, its population enslaved and sacrificed to the Dark Gods.Finding nothing alive on Urthwart, merely death and hideous Plague Zombies infected with the Curse of Unbelief, the Kasrkin prepared to withdraw. Suddenly, a frantic vox communication from their ships in orbit reported numerous vessels advancing on Urthwart from the Eye of Terror. The Kasrkin attempted to fall back to their dropships to return to their troop carriers, but it was already too late.The Imperial ships in orbit were either crippled or were forced to disengage and make speed for Cadia. There was to be no escape for the Kasrkin who were stranded on Urthwart as a massive vessel, larger than the most gargantuan capital ship of the Imperium, approached the doomed world: the Planet Killer.Few were aware of the existence of this monstrous ship, for it had been thought lost at the Battle of Kharlos II, during the Gothic War centuries earlier. Oblivious to their fate, the stranded Cadians could do nothing as the incomprehensible power of the Planet Killer was unleashed in a devastating lance of energy that annihilated the blighted world they were trapped upon into spinning pieces of molten rock.As Urthwart died, collapsing in on itself, a Chaos warfleet composed of hundreds of warships and hulking troop transports surged from the depths of the Eye of Terror, heralding the beginning of Abaddon the Despoiler's fearful 13th Black Crusade.Imperial naval experts began plotting worlds likely to be chosen as targets for the vessel's attentions. Intelligence gathered during the Gothic War indicated that the Planet Killer was a ponderous vessel, and its Armageddon Gun took a great deal of time to power up and exert its effect upon a world once it was functional.The vessel was likely to be accompanied by a large fleet, which would be employed to subdue and distract the Imperium's own naval forces until the Planet Killer could unleash its main weapon. All available Imperial naval assets had therefore been tasked with locating such a flotilla, and system defence pickets were put on high alert for any signs a large Chaos fleet approaching one of their worlds.The skies above the worlds of the Imperium turned black with innumerable drop craft as the dread forces of Chaos began their invasion. The Planet Killer itself, being used as Abaddon's flagship, drifted ever closer to the Cadian System. Terrible, mighty Chaos Space Marines trod the surface of worlds they had not set foot upon for ten millennia and their hatred and thirst for vengeance truly knew no bounds.The Imperial Navy, for long solar weeks forced to fight a desperate holding action against the seemingly endless waves of Chaos vessels, was eventually reinforced. A fleet the size of which has not been seen since the end of the Gothic War eight standard centuries earlier had been dispatched from Cypra Mundi, and staged itself at Belis Corona in preparation for a massive counter-push into the Cadian Gate.The arrival of this vast armada allowed those Imperial vessels that had been fighting continuously since the beginning of the invasion a brief respite. Severely depleted ship’s companies were bolstered through indiscriminate press-ganging, and hasty repairs and refits were undertaken on those vessels most in need of them.The Imperial reinforcements were split into battlegroups, each tasked with bolstering the defences in a specific sector. The regions around the Eye of Terror encompass many millions of cubic light years, and only by the concentrated application of resources in those areas in most desperate need could the Imperial Navy hope to make inroads and slow, stall, and eventually repel the Chaos warfleets plaguing the region.During the latter stages of the campaign, when Abaddon's fleet was seen approaching the Agri-world of Lortox, the Ultramarines Honour Company -- a specialised company of Ultramarines that had been stationed at the Cadian Gate for many millennia, rotating officers and warriors from Ultramarines companies elsewhere and also drawing from the Ultramarines' Successor Chapters -- distinguished itself with a bold, space-borne counter-assault against Abaddon's fleet as the Planet Killer closed with that Imperial world on the outskirts of the Agripinaa Sector.The action bought Lortox's Planetary Defence Forces time to evacuate a significant proportion of the population before the world was destroyed by the Despoiler's horrific weapon of planetary destruction. The Ultramarines Honour Company managed to succeed in crippling the Planet Killer, but it still had enough power to limp away.In the aftermath of the Lortox Evacuations, the Honour Company redeployed to Cadia and the surrounding star systems, launching a series of operations to hinder Abaddon's forces as they assaulted the Imperial positions. These attacks included a series of highly successful boarding actions against the lumbering space hulks being used to transport vast hordes of enemy troops to reinforce the Despoiler's siege of Cadia.It was a fool's dream to hope the Planet Killer could be found before it was brought to bear upon the Imperial forces. Without warning, it appeared in orbit over the world of Macharia.Though many could scarcely believe it, the world was destroyed by the massive vessel. It was lost, and with it millions of loyal and faithful subjects of the Emperor, dead at the hands of the Despoiler and his despicable weapon. Utter dread now descended upon the Imperial High Command.Despite the successes of the early weeks of the invasion, many had come to believe that this war might not be won in the short term. Where at first the Imperial forces fought to repulse the Despoiler, to deny him footholds upon their worlds, they now fought to keep him from overwhelming them entirely.This was a grim paradigm, and one the Imperial forces were not ready to accept. They believed Abaddon dare not destroy Cadia, as its pylons were reckoned intrinsic to the continued stability of the Cadian Gate. So the Imperium would stand and hold there, no matter the cost.At the height of the final Chaos assault on Cadia, a massive orbital battle took place between the Imperium and its Craftworld Aeldari allies and the forces of Chaos. The Imperium was still attempting to piece together the details of the battle, but the records currently remain so confused and incomplete that it may never be possible to learn the true details of what occurred.But during this final battle, the Planet Killer once again disappeared, and it is assumed to have made a hasty retreat towards the Eye of Terror, where it once again waits patiently until another opportunity to strike against the realm of the Corpse Emperor presents itself.