From Bred for War:
The Lords of Askellon quickly realised the potential for such skilled fighters, and soon the agents of the Missionarus Galaxia began the diligent and subtle process of indoctrinating the clansmen of Hrax into the Imperial Creed. In a few years, the High Marshals were shown the "proper" rites of devotion, and those who "survived" publicly swore new blood oaths to ... [the] Emperor. Shortly thereafter, the massive transport ships of the Departmento Munitorum arrived, and before long the first regiments of the Hrax Bloodknives left their world behind to "claim glory and honour" amidst the innumerable terrors of the Imperium’s countless battleields.