|Imperium (Dark Angels), formerly Necron
|Adeptus Astartes Recruiting World, Necron Tomb World
In M41 it was invaded by a combined force of the Necron Xonthar Dynasty, led by Overlord Varagon Drakvir, and the Death Guard, led by Typhus. The alliance between them was made as each would benefit from the Dark Angels losing control of Nymidae: for the Xonthar Dynasty they would claim Nymidae as their own, as it was unknowingly to the Imperium a Necron Tomb World, with countless Necrons sleeping beneath its surface, while the Death Guard would claim the Dark Angels' secrets that laid within their Fortress of Redemption.
They did not count, however, on the tenacity of the Dark Angels defending Nymidae, who were led by Grand Master Azrael, nor did they know that a Blood Angels force, led by Captain Tycho, would come to the Dark Angels' aid. Once the Blood Angels made planetfall, the two Chapters fought side by side and though they suffered heavy casualties, they defeated the Necrons and Death Guard's forces and drove them off of Nymidae.