Trisagion

The Trisagion was a part of a triumvirate of unique Imperial Abyss-class Battleships of special configuration, created and built in the early 31st Millennium. This vessel was constructed in secret during the latter years of the Great Crusade by the Renegade Dark Mechanicus faction loyal to Kelbor-Hal, the Fabricator-General of Mars' Mechanicum. This vessel was constructed for the Word Bearers Space Marine Legion, who were secretly ordered by the rebellious Warmaster Horus to bring their unfettered wrath down upon their hated rivals, the Ultramarines Legion. Following the destruction of his former flagship, the Fidelitas Lex, at the hands of an Ultramarines' retribution fleet at the Purging of Nuceria, Primarch Lorgar took the Trisagion as his new flagship.

History
During the opening days of the Horus Heresy, Primarch Lorgar had ordered his two most trusted advisors, First Chaplain Erebus and the Dark Apostle Kor Phaeron, to unleash their unfettered wrath against the Realm of Ultramar. This was done in retaliation for the humilation 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 at the Emperor's orders during the Great Crusade. The purpose of the Word Bearers' invasion of the Ultramarines' Realm of Ultramar in the Eastern Fringe of the galaxy was to tie down the XIII Legion and prevent them from reinforcing their fellow Loyalists as the Traitor Legions marched relentlessly on Terra itself. To this end, Lorgar commissioned the Fabricator-General of Mars, Kelbor-Hal in the construction of a mighty vessel of unique design, built on a scale never before seen by man. This gargantual vessel was christened by the Word Bearers as the Furious Abyss. The Furious Abyss was to be manned by one thousand Word Bearers Astartes. They were led by Fleet-Captain Zadkiel, a devout and zealous follower of the Word. He was charged by the Dark Apostle Kor Phaeron to lead the assault upon the world of Macragge, where they would strike the first blow against the hated Imperium of Man. But ultimately, Zadkiel failed in achieving his objective when the Furious Abyss was boarded by a small ad hoc force of Loyalist Astartes who proceeded to sabotage the massive vessel and destroy it, before its array of formidable weaponry could be brought to bare.

The Shadow Crusade
In the meantime, 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 and his World Eaters Legion into the rest of the Realm of Ultramar. They would go on to lay 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.

Blessed Lady & Trisagion
During one of their early campaigns, the joint Traitor fleet was to assault the war-world of Armatura, a vitally important world that fed the Ultramarines Legion with recruits and munitions. Its close-orbit played home to immense shipyards. Orbital bastions of linked gantries and docking maws drifted above the placid world. Above and beyond the shipyard was the first concentric ring of void defences. Here, weaponised satellites and fire platforms bristled with turrets, alongside independent landing decks for fighter craft in lockdown. Beyond those, the true defences began. Castles in the sky: great fortress-stations with their own racks of fighters and entire battlements given over to plasma batteries, laser broadsides and ship-killing lance arrays. In highest orbit, the outer sphere of satellites was a three-dimensional spread of solar panels, clockwork engines and slaved servitor brains all connected to vast long-range weapons arrays. Amidst that outermost sphere waited the Evocati fleet. While the Legion mustered at Calth, the XIII Legion’s war-world could never be left undefended. The Evocati was comprised of several thousand Ultramarines drawn from a dozen Chapters, awarded the highest honour of all: overseeing the operations of Armatura and the training of new recruits, commanding an Imperial fleet to rival any other.

It appeared that Lorgar's plans to assault Armatura were for not, for to attack the war-world they would need a vessel to rival anything humanity had ever wrought. The Word Bearers possessed such a vessel once -- Zadkiel's folly -- the Furious Abyss. But it had days earlier, close to the same moment Kor Phaeron struck Calth. Its corpse was probably still a shadow in the skies of Macragge, a monument to the Word Bearers' failure. Lorgar had told Zadkiel he was foolish to attack Macragge, but was so keen to bathe in glory, and all he ever hear were the whispers begging for revenge for what had occurred on Khur. So the Urizen had indulged him. But Lorgar had been underestimated, for he had planned for just such an eventuality. He had been planning the events that led up to the Horus Heresy for half a century. Beyond the deep void, past Armatura, reality opened. A warp-rift formed in space, far from both closing fleets. Something came through, something vast: a trident of dark metal immediately familiar.

The ship that ground into reality was a reflection of the slain colossus. A city of monasteries and cathedrals rose from its back with the reverence of clawed hands sculpted to clutch at the stars. Where most Imperial battleships were spears of crenellated intent and iron-ridged might, this was a fortress in space, borne on the back of a great trident. The central tine served as the vessel’s core: dense at the stern, encrusted with massive engines and tapering towards the prow, where it formed a pointed ram the size of lesser vessels. The trident’s adjacent tines formed smaller blade-wings, each one barnacled with broadsides and cannon batteries. If one were to clad the concept of spite in iron and set it sailing amongst the stars, it might approach the image of what burst back into the universe in that moment. It was, in every way, the Furious Abyss reborn. This mighty vessel was the Blessed Lady. This colossus was named for the Word Bearers' former confessor, Cyrene Valantion, the Confessor of the Word, and the lone survivor of the destruction of the Perfect City at the hands of the Ultramarines on the world of Khur. The Blessed Lady easily eclipsed the Gloriana-class flagships used by the Legions. But Lorgar's final secret was yet to be revealed. He had not simply had two of these mighty vessels built. As a second warp-slice ripped across the stars, another colossus was revealed. This was the Blessed-Lady's twin sister-ship, the Trisagion. The pair of dreadnought vessels even rivaled Imperial Fists' Primarch Rogal Dorn's precious Phalanx. Lorgar had secretly had three of these mighty vessels built for him.

The Blessed Lady and her twin sister, the Trisagion made a mockery of Armatura's orbital arrays, dismantling one of the best-defended worlds in the Imperium with barrage after barrage from their howling, flashing weapon decks. The ships’ size and scale rendered all countermeasures obsolete. For the first hour, nothing could punch through their shields. Nothing even managed to scrape their skin. It took the combined firepower of a battle-station, two orbital defence platforms and a suicidal ramming from an Imperial warship to finally burst the Blessed Lady's shields. She sailed on, oblivious to the thousands dying within one of the flaming monasteries on her back, for their agonies made no difference at all to a crew of half a million. The Word Bearers king ships made a mockery of the Ultramarines' defences and helped crush the Evocati fleet and to win the day at Armatura.

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. His cybernetic neural-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. 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 before 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 system. The Trisagion was waiting for them. Once on Nuceria, Angron had 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 bare. 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 traitor fleet sat patiently in orbit, awaiting the completion of the murder of an entire world. Without warning, 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. The XIII 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 XIII 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 it's own despite the number of enemy vessels arrayed against them. The king ship was like a fleet unto itself.