The Mordant Acid-Dogs are regiments of Imperial Guard raised from the Mining World of Mordant Prime, located in the Segmentum Obscurus. The Mordant Acid-Dogs specialise in subterranean tunnel fighting. They are typically deployed to combat zones where the Imperial High Command wishes to take advantage of their natural affinity for dark and confined spaces. The harsh conditions of their world breeds extremely tough and resilient warriors who are perfect for conscription into the military forces of the Imperium.
Mordant Prime is a world situation to the galactic north of the Eye of Terror, and is known for the mining of bioluminescent bacteria from which a unique, highly corrosive acid is extracted. Mordant is classed by the Adeptus Terra as a night world, and its surface is a barren wasteland, totally unfit for human habitation. The only reason humanity exists at all on the world is to mine the strains of luminescent bacteria that grows beneath the surface. Over the millennia, this process has formed a vast chain of caverns and tunnels that connect across the entire world. Within these tunnels mining clans extract the bacteria, culturing it in vast cavern-vats, to bleed off the most corrosive acids known to the Imperium. These extracts are shipped to Forge Worlds across the sector, where they find use in all manner of esoteric processes.
The peoples of Mordant can be split into two broad categories: the acid miners, and everyone else. The minors are organised into an ancient clan structure, and have total control over their business. They exploit cheap local labour; paying the workers barely enough to survive in the run down shanty-caverns they call home. Many of the disenfranchised citizens of Mordant turn to a life of organised crime, and gang violence is the only authority acknowledged amongst many of the deeper settlements. Only the skilled miners who are a part of the ancient organisation of Mordant mining clans, do not suffer from the extreme poverty experienced by the majority of the populace. The Mordant Regiments draw their conscripts from those unfortunate wretches that can no longer tolerate the harsh life of their world and the horrid living conditions, or from those who have earned the dire wrath of one of the many criminal gangs.
- Tactica Imperialis - A History of the later Imperial Crusades, pp. 71-