Nemendghast

Nemendghast was a former Imperial Industrial World that had lain in the outer reaches of the Vigilus System as part of an asteroid girdle. After the birth of the Great Rift, the world had been swallowed by that vast Warp rift and was conquered by the forces of the Black Legion.

It was swiftly transformed into a Hell-Forge for the forces of Abaddon the Despoiler, who used it to create Daemon Engines to supplement the Despoiler's coming assault upon the Sentinel World of Vigilus during the War of Beasts.

Abaddon intended to seize strategic control of the Nachmund Gauntlet from the Imperium of Man and use it to prevent the Imperium Nihilus from receiving easy supply or communications with the Imperium Sanctus. The planet's forges, particularly the primary centre of Daemon Engine production known as the Forge Infernus, eventually fell under the control of the Black Legion Chaos Sorcerer Vorash Soulflayer, the Master of Possession, and his armies of Daemonkin.

After the truth of what had befallen Nemendghast was relayed back to the Ultramarines Chapter Master Marneus Calgar who was leading the Imperial defence of Vigilus, he ordered an elite Vanguard Space Marine force from the Ultramarines 2nd Company known as Strike Force Shadowspear led by Captain Acheran to infiltrate the world and put an end to the growing threat. Though they failed to eliminate the Black Legion forces, Shadowspear disabled the Forge Infernus before a single Loyalist survivor escaped off-world to warn his Chapter of the grave new threat.

History
In a conflict that became known as the War of Beasts, Vigilus was beset from seemingly every angle. It all began with the arrival of SPEEDWAAAGH! Krooldakka. Despite arriving in numbers enough to drown Vigilus beneath a sea of Greenskins, the Orks were unable to breach the Bastion-class force fields that shielded the planet's vast continent-sized hivesprawls.

To assuage their boredom while stuck outside, the Greenskins engaged in hyper-violent races around the open wastes. Eventually, the force fields began to glitch and fail as the baleful emanations from the Great Rift interfered with their ingenious psy-tech. The war for Vigilus began in earnest.

Yet another danger lay hidden beneath the surface. An offshoot of the Pauper Princes Genestealer Cult had taken root in the seismic caverns beneath the hivesprawl of Megaborealis, biding their time to rise up. But the sudden change in circumstances on the surface, with the Orks now free to invade the Vigilite hivesprawls directly, forced the cult's hand. Even though the cult's uprising was premature, their influence had spread far and wide, and every hivesprawl was soon embroiled in insurrection from within even as they were assailed by Orks from without.

Seeing a world embroiled in a war on all fronts, other forces began to prey on Vigilus. A Saim-Hann warhost of Aeldari led an attack on the Vigilite capital of Hyperia, having become embroiled in a blood feud with the planet's ruling Aquilarian Council.

Druhkari raiders had long been operating from a hidden Webway portal in the frozen northern continent of Kaelac's Bane to steal away with slaves but escalated the frequency of their attacks after the arrival of the Ultramarines offered the Haemonculi the opportunity to capture Primaris Space Marines for their experiments.

At the head of the Ultramarines reinforcements was none other than Chapter Master Marneus Calgar, now mightier than ever after having crossed the Rubicon Primaris, to become the first of the older generation of Space Marines to become an enhanced Primaris Astartes. His tactical genius saw the tide of war on the embattled Sentinel World stymied, though its survival still hung by a thread.

To ensure that no other threats remained hidden within the Nachmund Gauntlet, in 7.230 post VCM.M41 Calgar dispatched what forces he could to search nearby worlds, root out any danger and rally any Imperial forces that could be found there.

One such planet was Nemendghast, an industrial world whose elliptical orbit had recently seen it re-emerge from the edge of the Great Rift. All attempts to hail the planet since its return had thus far failed to generate a response.

Calgar sent Strike Force Shadowspear to investigate. This elite force of Vanguard Space Marines was drawn from the Ultramarines 2nd Company and comprised storied Veterans from the Indomitus Crusade. They slipped covertly down to the planet's surface and were soon confronted by the terrible truth as to what had befallen Nemendghast.

The world belonged to the Black Legion. Where once there were vast factories dedicated to the glory of the Omnissiah, now there were Warp-tainted flesh pits and forges creating hideous Daemon Engines. Though he knew that Nemendghast was far beyond saving, Captain Acheran was determined to cripple the Black Legion's Daemonkin forces and prevent their strength from growing any further. Their best chance lay in the destruction of the Forge Infernus, a diabolical stronghold of the Chaos forces.

Though heavily outnumbered by Daemonkin warriors led by the Master of Possession Vorash Soulflayer, the Ultramarines Battle-Brothers launched a sabotage operation, crippling the primary corrupted forge. Their victory came at great cost; of the strike force, only the Vanguard Librarian Maltis escaped the planet to warn Calgar of the threat lurking at the edge of the Vigilus System, with his fellow Battle-Brothers recorded missing in action.