Purgation of Cathlevania

The Purgation of Cathlevania was a space hulk purgation campaign carried out by the Thunder Guardians] Space Marine Chapter to cleanse a daemon-infested derelict vessel when it entered their home system.

Background
Sometime in M35, a massive derelict vessel ripped it's way out of the Immaterium and into reality. This complameration of derelict vessels formed a mighty space hulk. This gargantuan vessel had become utterly corrupted by the insidious of Chaos - it's inner bulkheads transformed into living flesh of screaming souls and tendrils, while the remainder of the massive derelict was inhabited by foul creatures of the Immaterium and the daemonic. The might space hulk was commanded by the immortal sorcerer, Alucath, who deemed the massive vessel the Cathlevania. The Chaos Sorcerer was intent on conquering and enslaving the planets of the Orlrava Sector. However, he soon faced the might of the sector's guardians, in the form of the Thunder Guardians Space Marine Chapter.

The Chapter Master Alkalon, leading the Chapter's elite veteran marines, spearheaded the boarding operation against the space hulk himself. Using boarding torpedos and assault boats, the valiant Astartes successfully punched their way into the outer hull of the massive space hulk and fight their way into the innards of the corrupted vessel. Fortunately, the Chapter Master was accompanied by the Terminator armoured elite warriors, who fought furiously through the hordes of cultists, daemons and chaos spawn, intent on reaching the chaos sorcerer who commanded the damned vessel. The Space Marines encountered unspeakable horrors with the space hulk, but their ferocity and determination saw them carry the day, though they paid a high price in the lives of their fellow battle-brothers.

In the end, only the Chapter Master and Galgix, Alkalon's long-time friend, were the only two remaining Thunder Guardians left. It was said the sorcerer Alucath taunted the Space Marines the entire way, even singing as he wandered the halls of the massive space hulk, but he could not stay hidden for long from the vengeful Alkalon, who slew the foul sorcerer himself. With the death of the sorcerer, a massive warp rift opened and began to swallow the Cathlevania. The two surviving Space Marines just barely escaped the hellish confines of the space hulk, when it was pulled into the Immaterium and disappeared. However, this was not the last they would see of the slain Chaos Sorcerer, as the Cathlevania would return down the millennia - with a resurrected Alucath aboard - to plague the Imperium again and again.