Szaeyr Deathwatch Crusade
A Deathwatch Crusade is virtually unheard of in recent times, but not entirely unprecedented. Partial records remain of a Crusade undertaken in the 36th millennium against the Autocracy of Szaeyr, an extended alien/human coalition of worlds in the trailing reaches of Segmentum Tempestus. It appears that the level of cooperation and integration found there between human societies and that of the sauro-form Sza was so heretical that Watch Commander Balhus took it as a personal affront.
Rather than expose regiments of the Imperial Guard to such blasphemies, Balhus sought and was granted dispensation to call a Deathwatch Crusade. He summoned Deathwatch Battle-Brothers from across the Imperium to obliterate the Autocracy of Szaeyr. By the remaining accounts, Balhus' call brought the equivalent of a full Chapter of Deathwatch Battle-Brothers who descended on the Szaeyr in a whirlwind of fire and blood. The outcome of the crusade is lost in the mists of time, but with the amount of firepower that the Deathwatch brought against them, it cannot be imagined that the Autocracy of Szaeyr endured for long under the onslaught.