Desecration of Mathrica

The Desecration of Mathrica was an Imperial campaign that involved three companies of the Astral Levithans Space Marine Chapter, which came to the aid of the beleaguered Imperial shrine world of Mathrica, located in the Rathmein System, that was under siege by a combined Chaos fleet consisting of both the Word Bearers and Worlds Eaters Traitor Legions. Outnumbered and outgunned, the Astral Leviathans refused to see an Imperial world of such importance fall into the clutches of the Dark Gods, and therefore enacted the most brutal of doctrines, and subjected the doomed world to Exterminatus. Though the Chapter sacrificed all three companies in the process, they managed to slaughter millions of heretics in the process - a resounding, if somewhat pyrrhic, Imperial victory over the Forces of Chaos.

History
The Astral Leviathans 1st, 3rd and 5th companies respond to imperial calls for aid in the Rathmein System. Upon arrival they were quickly engaged by a combined Traitor forces comprised of the World Eaters and Word Bearers Traitor Legions. After six hours of brutal naval conflict and boarding actions taken by the World Eaters, the battle barge Scorched Blade takes position over the Shrine World of Mathrica. This world was under the protection of the elite 1st Company flagship and three badly damaged strike cruisers. Not willing to see a world of the Imperium fall into the hands of the Ruinous Powers, the Imperial vessels enacted Exterminatus and launched a relentless salvo of incendiary torpedoes which ignited the planet's atmosphere and slaughtered millions of heretics at the cost of three companies and the four penal legions involved.