Chaos Invades Decskull's Empire

System CRP-1089. A dim radiation blasting red dwarf deep within wilderness space, Ultima Segmentum, north of the great rift. The Imperium believes the system is dead. They are wrong. 

Habitable Worlds. 1 moon 1 planet

The planet: Inner part of habitable zone. Warm desert like conditions. Later known as BOD by the Orks. Chronically infested by Tyranids. 

The moon: Outer part of habitable zone. Later known as Morkheim by the Orks. Chronically infested by zombies. Possible former plague world. 

A tribe of orks and free booters settled on BOD that were caught up in a warp storm fleeing a tyranid onslaught. When the Nids followed, the orks held off the onslaught and crippled the hive ships with wave after wave of fighta bombers. The tyranids infested BOD but were forced to retreat from the system.

This led a significant number of orks to migrate to Morkheim, where they found bountiful scrap and were able to start rebuilding their fleet which had been mostly destroyed during the tyranid incursion. 

After the Great Rift opened, Chaos ships began transiting the system as a jump point to invade Imperial space. After a Chaos patrol was ambushed and critically damaged, by ork ships Chaos launched an all out invasion.