War on Mondas

The War on Mondas was an Imperial castigation campaign carried out against the icey world of Mondas in the Scarus Sub-Sector. The Death Templars were sent to carry out the will of the High Lords of Terra, but quickly discovered that the population of the planet had already been culled by the Heretic Astartes of a large Iron Warriors Chaos Warband. The two opposing sides fought in a brutal and bloody-handed conflict, which unbeknownst to both sides, woke up legions of slumbering Necrons beneath the planet's surface, for the planet was a long dormant Necron Tomb World. Soon, all three sides were engaged in fierce conflict. Recalling his forces, the Lord Marshal of the Death Templars withdrew his forces while the Heretic Astartes and Necrons were heavily engaged with one another. Taking no chances, he then ordered an Exterminatus upon the doomed world, ensuring the destruction of their foes.

History
The Death Templars received a distress message in the form of a garbled astropathic relay from the abandoned Imperial Ice World of Mondas in the Scarus Sub-Sector. When they finally arrived, the Death Templars discovered that the Iron Warriors had already culled the remainder of the planet's population. After reconnoitering the planet, the Chapter's Scouts quickly discovered that the Iron Warriors were busy excavating the ice caverns below the planet's surface in an effort to discover some unknown, ancient technology that would enable them to defeat the forces of the Imperium. However, unknown to both the Death Templars and the Iron Warriors, the world of Mondas was in actuality, a Necron Tomb World. The Iron Warriors' seismic activity caused by the use of explosives to delve ever deeper into the planet's crust had awoken the Necrons from their slumber. The Iron Warriors were forced to fight for their very survival.

Lord Marshal Valdar led a lightning assault, intended as a crippling alpha strike, but was instead blunted by a series of impeccably-planned Necron ambushes on the Space Marines' Drop Pod and Thunderhawk drop zones. Soon the frozen caverns echoed to the roar of explosions as the Death Templars and Necrons fought a series of brutal close-assault battles over a period of six months. The Necrons were tenacious, and the never-ending tide of Necron Warriors soon resulted in a stalemate. Recalling his forces, the Death Templars departed the surface of the ice planet, and the Lord Marshal soon after ordered an Exterminatus upon the doomed world, which eradicated both the remaining Iron Warriors and the Necron forces.