Rust Legion

Overview
The Rust Legion is a self-declared Grand Company and splinter warband from the Iron Warriors legion. They are unusual for a warband of Iron Warriors lineage in that they are singularly devoted to the Chaos god Nurgle. Led by self-proclaimed 'Warsmith' Griegus Bak, the Rust Legion have been seen on battlefields of siege and attrition across the Ultima Segmentum.

History
"Blind fools, all of them. They sneer and spit, but who is now the strongest on the siege line? Who is now capable of laying the greatest fortresses low with half the number of troops as our brethren? Let them keep their iron. Rust always triumphs in the end." ~ Griegus Bak, 1st Warsmith of the Rust Legion

The Rust Legion are a comparatively new warband, formed in the aftermath of the War of Rust and Ruin in early M42. The conflict saw the Iron Warriors pitched against the Death Guard for control of the Temple of Ascension on the world of Dysactis. Despite inflicting massive losses upon the forces of the Death Guard, the Iron Warriors were eventually forced to withdraw after the maladies of Nurgle gradually rendered their forces incapable of continuing to fight.

One of the surviving Iron Warriors from this war was a Captain by the name of Griegus Bak, who barely escaped death himself in one of the last rearguard actions of the war. Equally enraged and impressed by the resilience of the Death Guard forces he had faced, Griegus began to impress upon his troops the benefits of Nurgle's gifts in resilience and strength. His commanders were initially reluctant, constrained by the legion's cultural abhorrence to the potential for mutation in pledging too closely to any one Chaos god. However, the promises of greater endurance were incredibly tempting to a siege-oriented force such as the Iron Warriors, and Griegus' misguided belief that he could control the influence of Nurgle eventually led to the warband's conversion to worshippers of the Plague Father.

A ritual was conducted by Griegus' entire company of Astartes, held in secret lest they be discovered and destroyed by other forces within the Grand Company to which they were pledged. Griegus' overconfidence in controlling the effects of Nurgle was proven evident. The ritual spiraled out of control, and every Astartes of the company became trapped inside suits of armour sealed tight by rust as hard as ceramite. Griegus himself watched his body warp and merge into his armour, forever rendering him as a half-desiccated corpse of iron and rust.

The ritual was noticed by the other Iron Warriors of the Grand Company, and Griegus' troops were forced to fight their way out of their own fleet and into exile. Loathing his own lack of strength in controlling Nurgle's mutations and enraged at the perceived betrayal of his legion brothers, Griegus declared himself a Warsmith of a new Grand Company, which took the name of the 'Rust Legion'.

The warband declared a vengeful crusade against their former brethren and the Death Guard, determined to vindicate their actions by demonstrating their improved prowess in the siege and attritional warfare they had sought to master further through their pledge to Nurgle. The Crusade of Rust began to carve its way across the Ultima Segmentum, seeking to establish a trail of destruction across the stars that would stand in testament to the warband's strength.

Argyle IV Campaign
Battle of Arakor City - An uneasy alliance of the Rust Lords and a Slaaneshi daemonic host attacks an Ork Waaagh occupying the burned-out remains of Arakor City on Argyle IV, an industrial world on the edge of the Great Rift. The battle disturbs a slumbering Necron tomb, some of whose occupants join the hostilities with an apparent focus on destroying the Chaotic insurgents over the Ork defenders. Slaaneshi daemons battle through the Ork Killer Kans defending the city outskirts whilst the Rust Lords bring their primary focus to bear upon the awakening Necrons. The battle results in a victory for the Rust Lords and their daemonic allies, who then sack the remnants of the city for supplies, slaves, and sacrifices.

Assault on Hector Rex - Word reaches the Rust Legion that Inquisitor Lord Hector Rex and a retinue of the Inquisition has arrived on Argyle IV for unknown reasons. Seeking to strike a blow against the Imperium that will cement the Rust Legion's infamy, Warsmith Griegus Bak rallies a vanguard of the Rust Legion and calls once again upon the support of the Slaaneshi cult operating on Argyle IV. The combined forces of Heretic Astartes and daemonic creatures assault the Inquisitor mid-journey, only to discover that Rex is accompanied by a bodyguard of Blood Angels. A pitched battle ensues, with the Blood Angels fighting valiantly against daemonic claws and heretic guns.

Despite noble efforts, the Blood Angels retinue was slain almost to a man, and Inquisitor Rex's party was forced into direct combat. As the bolters and lascannons of the Rust Legion pounded against the Inquisitorial bodyguard, Rex unleashed his final gambit. Channeling the potent psychic powers of his retinue, Rex managed to invade the mind of Griegus Bak himself, taking control of the Warsmith's body for a brief period. Before Griegus could regain dominion over his actions, Rex commanded the Warsmith turn his weapon upon himself, slaying the Rust Legion leader with a righteous burst of plasma fire. Having been decapitated of its command structure, the Rust Legion was forced to fall back. The Inquisitorial retinue managed to slip away during the confusion, living to fight another day.

Siege of Blackhall - Newly-proclaimed Rust Legion Warsmith Bucharis Balthazar sets his sights upon Lord Inquisitor Rex in vengeance for the death of Griegus Bak. The Inquisitorial party is tracked to the fortress of Blackhall, long thought abandoned but in actuality a secretive Inquisitorial facility for interrogation and experimentation. Summoning every daemonic entity possible from the sorcery at his disposal, Balthazar attacks Blackhall with an onslaught of Nurgle and Slaanehsi daemonic hosts alongside the Rust Legion.

At first, Blackhall appears only sparsely defended by a force of Guardsmen and Scions. Once again however, Lord Inquisitor Rex reveals an unexpected element to his defence. He orders the dungeons of Blackhall opened onto the battlefield, releasing forth a tide of Dark Eldar warriors imprisoned there as laboratory rats for some unknown purpose. Desperate for their freedom, the perfidious Eldar charge headlong into the Chaos assault, tying up the attacking forces long enough for the Inquisition to marshal its defences. The Chaos host is forced to call off its attack when Inquisitorial reinforcements arrive in orbit with orders to either destroy or relieve Blackhall dependent upon the state of its defences. Deeming Blackhall within reasonable chance of salvation, reinforcements are landed to assist the defenders. The Chaos forces retreat once again, frustrated once more by the ingenuity of Inquisitor Lord Hector Rex.