Codex: Chaos Space Marines (2017), p83 — Plague Marines

Plague Marines are Chaos Space Marines who have sworn themselves to Nurgle, the Chaos God of pestilence and entropy. The first Plague Marines were warriors of the Death Guard Legion, trapped in the warp upon their spaceships when the virulent Destroyer Plague struck their fleet. Mortarion and his Legion offered themselves up to the service of the Lord of Decay in return for their lives. Their bodies became bloated and swollen with the corruption festering within them, but they no longer felt the agony of the warp-pox and did not die from its horrific symptoms.

Since then, many Space Marines have dedicated themselves to Nurgle, though few achieve the vaunted ranks of the Death Guard. Those who truly wish to join this most foetid of cadres must first swear loyalty to the Primarch Mortarion - only then will Nurgle bestow upon them the corrupting ague that created the Plague Marines. Outside of the Death Guard, a favoured few Sorcerers of Nurgle know the secrets of the Plague Marines, and Abaddon of the Black Legion has won many of these spellcasters to his cause. In return for fealty and long service, these blight-mages will bestow their pestilent gifts in the Warmaster's name.

Regardless of allegiance, all Plague Marines have disgusting, rotted bodies that stink of decay. The putrescent slime that oozes from their many weeping sores corrodes their armour and burns their skin, but despite their horrific disfigurements, the Plague Marines are fearsome warriors indeed. Their rotting brains are inured to the agony of bodily corruption, making them all but immune to the pain or debilitation caused by the weapons of the enemy. Not for nothing are these repugnant footsoldiers considered the most resilient of all the Chaos Space Marines.

The Plague Marines prefer short-ranged firefights, where they can truly appreciate the festering carnage they inflict upon their enemies even as they laugh off the bolts and las-blasts directed back at them. The blessed reek of corruption, the sight of freshly suppurating flesh and the blossoming gore of an infected wound - these are things to be grateful for. Those who do not appreciate Grandfather Nurgle's bounty are soon laid low. Should the enemy close to within arm's reach, the Plague Marines will attack with plague-riddled knives, and even hurl toxic blight grenades - vile inventions containing virulent toxins that eat away at armour and fill the air with thick clouds of blinding spores. The most ostentatious blight grenades are 'death's heads' made from the severed remains of fallen enemies, each cranium filled to the brim with a cocktail of disease before being sealed with ancient wax.

As well as fighting at the behest of the Lords of Chaos, the Plague Marines dedicate their lives to spreading corruption and decay across the galaxy. The fleets of Nurgle that spew from the warp spread contagion and pestilence across dozens of star systems. Once the plague ships are abandoned or their crews finally destroyed, the hulks float back to the warp and eventually, perhaps guided by the hand of Nurgle himself, find their way back to a plague planet, where they are re-crewed for a new wave of attacks.

The Cloud of Flies

During a plague ship's journey through the warp, the interior of the craft erupts with large, furry black flies that fill its holds with their decaying carcasses. When the plague ship reaches a world, the Plague Marines disembark to make planetfall. As soon as their transports' hatches open, a thick cloud of insects is released, ready to spread its foulness over a virgin planet. The fly is sacred to Nurgle, for it feasts upon the rotten and the foul. Even one such beast can carry upon its little limbs a cornucopia of infections and viruses, spreading the gifts of contagion to everything blessed by its visitations. When they come on in a great swarm, these diminutive creatures can spread a plague with incredible speed, infecting, infesting, hatching and multiplying in celebration of Nurgle's bounteous cycle with each new day. The symbol of the fly is therefore common amongst the Plague Marines, with elements of its form echoed on the mutant bodies of the Death Guard, Nurgle's chosen sons.