Callistos Exculpation

The Callistos Exculpation was a joint-Imperial excoriation carried out by both the Bears of the Claw and Iron Blood Chapter against the notorious Black Devourers and Obsidian Suns Chaos Warbands during the Callistos Campaign, upon the sector capital world of Athalios.

History
When the worlds of the Callistos Sub-Sector fell under siege by the notorious Black Devourers Chaos Warband, their arch-rivals - the Iron Blood Chapter - answered the pleas of the Sector Governor for aid against these vile Heretic Astartes, and according to records, deployed enmasse to face this dire threat. Upon the sector capital world of Athalios, these two bitter foes faced one another on the battlefield. But the Black Devourers laid a cunning trap for their hated foes, having forged a secret alliance with the Tzeentchian Chaos Warband - the Obsidian Suns. Using their foul sorcery, the Tzeentchian Warband hid themselves behind malefic glamours, revealing themselves only when the Iron Blood Chapter had been wholly drawn into their deadly trap. As the Black Devourers herded the loyalist Space Marines, the Obsidian Suns launched an attack on their vulnerable flank. Hoards of Rubric Marines marched in perfect lockstep, laying down a heavy barrage of bolter and warpflame fire as the Warband's Exalted Sorcerer overlords floated above them upon their cursed discs, casting deadly spells as they chanted in cursed daemon tongues, bringing destruction and ruin to the valiant Iron Blood Astartes. Sensing their inevitable doom, the remaining Iron Blood Astartes formed a phalanx-formation and prepared to sell their lives dearly, determined to take as many of the enemy with them to hell. But it was at this moment that a miracle occurred. A force of silver armoured Astartes bearing the livery of the Bears of the Claw appeared unexpectedly and attacked the Obsidian Sun forces from behind. Forced to redeploy, as they found themselves faced with the prospect of having to make a breakout, the Rubric Marines were commanded to make straight for the Bears, as the Tzeentchian sorcerers judged the new arrivals as the lesser threat of the two Space Marine forces. The Bears of the Claw stood resolute in the face of the storm of eldritch firepower, against which the formidable Astartes stood seemingly impervious. The Iron Blood were able to take advantage of this temporary distraction and were able to press the attack on the enemy's rear as the Bears held the Obsidian Suns Warband in place. The Heretic Astartes were destroyed in short order, caught between the immovable anvil of the Bears and the irresistible hammer of the Iron Blood. Faced with annihilation, the Exalted Sorcerers cast a powerful spell and teleported their Obsidian Suns away from the field of battle in a blinding flash of incandescent light, leaving their Black Devourers allies to face the wrath of both Space Marine Chapters, alone. The allied loyalist Astartes forces then focused their undivided attention upon the remaining Chaos Warband, pressing the attack against the outnumbered Heretic Astartes. Knowing that the battle was lost, the Black Devourers withdrew from the field of battle and fled the surface of Athalios. As soon as the Forces of Chaos were defeated and the Imperial forces were victorious, without preamble, the Bears of the Claw departed just as quickly as they had arrived, to continue their neverending Crusade.