Trisagion - Purging of Nuceria: During this campaign of destruction, Lorgar had come to realise that over the course of their Shadow Crusade, Angron's temperament and mental stability had steadily grown worse. The cortical implants known as the Butcher's Nails were killing him faster than Lorgar had originally imagined, faster than anyone realised. The rate of degeneration had accelerated very quickly in the months after the Battle of Calth. The implants had never been designed for the peculiar genetics of a Primarch's brain. Angron's physiology was trying to heal the damage produced by the implants as the Nails bit deeper. To save his life, Lorgar convinced the Lord of the World Eaters to go back to his homeworld of Nuceria, which lay near the Realm of Ultramar in the Ultima Segmentum. The overlords of the gladiatorial games on that world who had first hammered the foul device into Angron's 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 from the Dark Gods, whether he wanted it or not.Twenty-seven days after the Conqueror and the Fidelitas Lex left Armatura in ashes, they broke from the Warp at the edge of Nuceria’s star system. The Trisagion was waiting for them. Once on Nuceria, Angron paid his respects to his fallen brothers and sisters amongst the Nucerian gladiators he had once fought beside, whose bones now lay exposed to the elements on the Desh'elika Ridge where they had died. The painful memories of that day, long ago, were too much for the Primarch to bear. After paying a visit to the city-state of Desh'ea to see who ruled the Nucerian city-state that had once claimed to own him, he became enraged when he was told the tale of how he had fled at the Battle of Desh'elika Ridge, and the subsequent massacre of the rebel army in the mountains. The rebels had died to a man in his absence. Enraged by the lies that had been told about him over the last century, Angron ordered his Legion to kill everyone in the city. Then they were to kill everyone on the planet.As the World Eaters and Word Bearers lay waste to Angron's homeworld, the Traitors' fleet sat patiently in orbit, awaiting the completion of the murder of an entire world. Without warning, Roboute Guilliman's Ultramarines 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. 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.Meanwhile, the Trisagion held its own despite the number of enemy vessels arrayed against the Word Bearers' fleet. The great Abyss-class Battleship was like a fleet unto itself. However, Lorgar's flagship, the Fidelitas Lex, was already a ruin, its armour pitted and cracked, its Void 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 Macro-cannons, 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 XIII 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. But the Lex's destruction was inevitable, as the flaming wreckage of the once-proud flagship crashed to the planet's oceans below.With the defeat of the Ultramarines and their Primarch on the surface of Nuceria at the hands of Lorgar and Angron, who had ascended to become a Daemon Prince of Khorne as a result of Lorgar's machinations, the Ultramarines retribution fleet recovered its troops and then withdrew from the system to lick its wounds. Following the completion of the Purge of Nuceria, Lorgar took the Trisagion as his new flagship. The ultimate fate of the Trisagion following the void battle at Nuceria is unknown in the fragmented Imperial records currently available from this time.