Fidelitas Lex - Shadow Crusade and the Purge of Nuceria: During the opening days of the Horus Heresy, Lorgar had ordered his two most trusted advisors, First Chaplain Erebus and the Dark Apostle Kor Phaeron, to unleash their wrath against the Realm of Ultramar. This was done in retaliation for the humiliation the XVII Legion had been forced to endure by being forced to kneel in disgrace before the Emperor and Roboute Guilliman and his Ultramarines on the world of Khur by the XIIIth Legion at the Emperor's orders during the Great Crusade.The Word Bearers proceeded to achieve a monumental victory at the Battle of Calth which ensued. The Ultramarines Legion was badly crippled and no longer presented a viable threat to Horus' plan to drive on Terra. Erebus had managed to complete his blasphemous ritual on Calth's surface, which summoned the beginnings of the sorcerous Ruinstorm to the galaxy's Eastern Fringe -- a monstrous Warp Storm larger and more destructive than anything space-faring humanity had witnessed since the days of the Age of Strife.Simultaneously, with the Word Bearers' assault on Calth, Lorgar and the more reliable Word Bearers under his command launched a second offensive, a joint Shadow Crusade with his brother Angron's World Eaters Legion into the rest of the Realm of Ultramar, laying waste to the Five Hundred Worlds with reckless abandon, slaughtering twenty-six worlds in rapid succession.This was to ensure the success of the sorcerous Ruinstorm, which would ultimately split the void asunder, dividing the galaxy in two and rendering vast tracts of the Imperium impassable for centuries, effectively cutting Ultramar off from the rest of the Imperium. This prodigious Warp Storm would deny needed reinforcements to the Loyalists as Horus drove on Terra in an attempt to overthrow the Emperor of Mankind. Nothing from Terra would get in and nothing would get out. Not even an astropathic whisper would be able to pierce this storm of Warp energy bleeding into realspace.To save the life of his brother Angron, Lorgar convinced the Lord of the World Eaters to go back to his homeworld of Nuceria. The overlords of the gladiatorial games on that world who had first hammered the foul device known as the Butcher's Nails into his skull would know more of the implant's function than the Traitor Legion's savants and the Dark Mechanicum.The two primarchs would learn all that was known about the Nucerians' insidious cortical implant technology, and then they would burn that loathsome world until its surface was nothing but glass. Angron would finally take the vengeance he pretended to no longer desire. Whether Angron fought him, hated him or trusted him, mattered little to Lorgar, who intended to drag Angron into the immortality that he deserved before the Dark Gods whether he wanted it or not.Roboute Guilliman's Retribution Fleet, which had been tracking the rest of the Word Bearers Legion in the wake of the Battle of Calth, finally caught up to the Traitors upon Angron's homeworld of Nuceria, which the World Eaters Legion were preoccupied with wiping clean of all life in vengeance for the treatment the Nucerians had merited out a century before to Angron. The XIIIth Legion warship Courage Above All, Guilliman's temporary flagship, broke Warp at the system’s edge, at the head of a large void armada consisting of 41 vessels. The Ultramarines armada looked wounded, cobbled together from separate fleets.It was not a dedicated interdiction war-fleet, but clearly a ragtag strike force, a lance thrust to the enemy’s heart. Guilliman himself had done the best he could with limited resources. The XIIIth Legion's Cruisers and Battleships ran abeam of the enemy fleet for repeated exchange of broadsides, offering targets too big and powerful to ignore, while the rest of the Ultramarines fleet used calculated Lance strikes from safer range. The armada then divided its assault potential, doing its utmost to destroy Lorgar's flagship Fidelitas Lex, and attempted to take the World Eaters' flagship Conqueror in a boarding action.But the Ultramarines' warships not only fought a void war, they also attempted to take the fight to the surface of Nuceria, for this attack was personal. The Ultramarines had come for revenge against Lorgar and the Word Bearers, just as they had pursued Kor Phaeron all the way to the Maelstrom on the other side of Ultramar.Several Ultramarines warships attempted to make a run on Nuceria, haemorrhaging Drop Pods, landers and gunships, forcing planetfall by any means necessary. The Ultramarines fleet swept over and against the Traitors like an insect horde. But the tenacious commander of the Conqueror, Lotara Sarrin, put up a difficult fight and destroyed a number of Ultramarines vessels that attempted to make a run for the surface.Though the World Eaters' flagship transformed a number of the smaller vessels into flaming wreckage, the Ultramarines eventually punched through her tenacious defence and managed to land troops on the surface of Nuceria.Meanwhile, the Fidelitas Lex was already a ruin, its armour pitted and cracked, its shields a memory. The cathedrals and spinal fortresses barnacling along its back were gone, laid waste by the Ultramarines' incendiary rage. The XIIIth Legion's armada attacked in strafing runs and protracted exchanges of broadsides, trading fire with the superior warship and accepting their own casualties as the cost of bleeding the bigger vessel dry. Each assault left the Lex weaker, firing fewer turrets and cannons, taking punishment on its increasingly fragile armour. But she fought on.Crawling with smaller ships, the Lex lashed back with its remaining Macrocannons, rolling in the light of its own burning hull. Guilliman guided the battle from the command deck of Courage Above All, and had decided that the Lex would die first, killed in the death of a thousand cuts and swept from the game board, while the Conqueror would be boarded and killed from within.In the course of the battle in Nucerian orbit, the Conqueror could not rise to its sister-ship's defence. Both Traitor Legion flagships fought alone, starved of support and suffering the endless attacks of the XIIIth Legion's ragged armada. Salvation Pods streamed from the Lex's sides and underbelly, along with heavier Mechanicum craft and bulk landers.With the Legionaries of the Word Bearers already on the surface, the ship's human population fled in the vessel's final minutes. And still the great vessel fought -- rolling, turning, raging. The Ultramarines Cruisers that drifted past burned as badly as the warship they were killing. This void battle was a form of dirty fighting between warships, too close for the neat calculations of ranged battery fire. Instead, it was an up close and personal slugfest.The Conqueror could not rise to its sister-ship's defence. Both flagships fought alone, starved of support and suffering endless attacks by the XIIIth Legion's ragged armada. The Lex knew it was doomed, and so, before it reached Nuceria's atmosphere, the order to abandon ship was given, marking twelve kills.As the fighting raged on the planet's surface, the burning shell of the Fidelitas Lex cut through the clouds into the planet's atmosphere, shuddering on its way east, rolling ever downwards, achingly slow for something of such scale. The weight of the Fidelitas Lex's massive plasma engines dragged the stern down first, colliding with the Nucerian ocean's surface far from shore, and at last bringing the great vessel to rest deep within its watery embrace.