Battle of Malbede
The Battle of Malbede was fought in 963.M41. Originally fought between the Ultramarines Space Marine Chapter and an expeditionary fleet of the Tau Empire for control of the world of Malbede, the conflict took a dramatic turn when the battle awoke Necron tombs hidden under the planet's crust. Facing a common enemy, the Ultramarines and Tau joined forces to defeat the emerging Necrons. In the wake of the battle, Chapter Master Marneus Calgar initiated Exterminatus on the cursed world, but generously allowed the Tau to evacuate before the planet was destroyed.