Realm of Chaos: The Lost and the Damned (1990), p256 — Chaos Renegades of Nurgle

In the third year of the Horus Heresy the rebel Death Guard Chapter was marooned in the warp while attempting a long-range jump to Earth. Months passed while the fleet's Navigators searched for a warp-tide that would bring them back to the material universe. Meanwhile a mysterious contagion began to spread from ship to ship. The stinking pestilence bloated the gut, distended the flesh, and turned its victims rotten from the inside. Eventually the Chapter's Primarch Mortarion became infected and in his delirium he called upon the Powers of Chaos to aid the Space Marines. Mortarion's fevered ravings were answered by Nurgle, and Mortarion became Nurgle's Champion and eventually the Daemon Prince Mortarion, Lord of the Plague Planet. The Plague Planet he rules over lies deep inside the Eye of Terror. From this dark and slimy orb Mortarion launches fleets of Plague Ships into the warp to carry their contagions through the galaxy. On board are Champions of Chaos and their followers from the Plague Planet accompanied by warriors of the ancient Death Guard - the heinous Plague Marines of Nurgle.

The Death Guard

The Death Guard Chapter was one of the original twenty Space Marine Chapters founded by the Emperor. During the Horus Heresy the Chapter joined the rebel Warmaster Horus and took part in many battles against the Emperor's forces. Their commander, Mortarion, became an open worshipper of Nurgle when the entire Chapter was trapped inside the warp and ravaged by plague. Subsequently he led his Space Marines in a merry dance of destruction over a score of planets. As disease began to disfigure the Marines, their appearance changed into the disgusting form they still bear today. Now te once tall and erect Space Marines of the Death Guard are the Plague Marines of Nurgle. Their flesh bubbles with corruption, their innards spill through lesions in their putrid skin, and their bodies ooze with sticky slime.

Following the death of Horus and the effective end of the Heresy, Mortarion fled with the remnants of his Chapter into the Eye of Terror where he received Nurgle's ultimate reward and became the Daemon Prince Mortarion. He rules over a Plague Planet where sickness and pestilence are the norm, where miasmic clouds being corruption and death and where the diseased pray to Nurgle for relief from their constant agony. Some of them are favoured and become Champions, and then fight among themselves for mastery and the chance to become Daemon Princes in their own right. The Plague Marines rarely interfere in battles between rising Champions. In fact they are not commonly seen by the world's inhabitants except during the time when new Champions are selected to fight with the Chaos Renegades. Most of their time is spent attending on Mortarion or carrying out his wishes, spreading new diseases and travelling to other worlds to carry Nurgle's plagues to new victims.

The Plague Fleets

Not even the ministrations of advanced technology can entirely eradicate the dangers of disease on long space voyages. A ship travelling between far flung planets always risks contamination by alien viruses or mutated bacteria. Such perils can quickly infect and slay the crew, or incapacitate the ship's Navigator stranding the ship in the warp. The empty husks of Plague Ships drift through the warp, sometimes for thousands of years, until they are drawn to that bosom of pestilence which is the Plague Planet of Mortarion. Here they are gathered into Plague Fleets and filled with the diseased followers of Mortarion before being cast back into the warp to spread their pestilence throughout the galaxy.

The Plague Fleets carry followers of Nurgle to inhabited planets where their destructive raids are inevitably followed by an outbreak of a no less destructive contagion. Once the Plague Ships are abandoned or their crews finally destroyed, the hulks float back into the warp where the currents carry them back to the Plague Planet.

The Cloud of Flies

During the Plague Ships' journey through the warp the insides of the craft erupt with large furry black flies. They burst from every surface, covering the interior of the ship, filling whole rooms with their decaying carcasses. When the ship reaches a new world the Champions and their followers prepare to disembark by landing craft, teleport, or by landing the ship itself. As soon as the ship's hatches are opened a thick black cloud of insects is released, each a tiny bearer of disease ready to spread the foulness of Nurgle over a virgin planet. Even when the Marines disembark by teleporter enough flies are transported to form a dense cloud of choking blackness.