A faction of the military for the Empire of Man in the Warhammer 40000 universe.

They're fanatical troops based on German gas warfare troops from World War 1, and are masters at siege warfare. Their home planet had a vicious revolt against the Empire's rule. The pro-Empire forces eventually won but at great cost, turning the world into a radioactive hell, and have since turned to fanaticism in the Emperor's name in repentance for the revolt.

further information