Abaddon the Despoiler may have led a unified Chaos warfleet in the service of Chaos Undivided during the Gothic War, but this is the exception, not the rule, for the forces of Chaos possess no unified naval force like the Imperium of Man.
The origins of the Chaos Warfleet can be traced to the bygone Age of the Imperium and the Great Crusade of the 30th and early 31st Millennia, launched from Mankind's birthworld of Terra into the stars to reunite the disparate tribes of humanity into the burgeoning Imperium of Man.
The Great Crusade was the largest and most ambitious military endeavour ever undertaken by Mankind. As mighty and valiant as the hosts of the Emperor were, this epic undertaking would have been entirely impossible without the countless thousands of Warp-capable vessels that transported hundreds of thousands of the superhuman warriors of the Space Marine Legions and many millions of Imperial Army soldiers from one star's light to the next.
The Great Crusade saw a staggering array of vessels constructed, reclaimed or pressed into service. Some were used for a matter of solar months before being declared obsolete or wearing out and degrading to destruction, quite apart from losses incurred in battle, while others gained a permanent place in the canon of war, with successful designs endlessly copied and modified as the decades progressed.
The first vessels to enter the service of the Imperium were constructed in the orbital foundries of Terra, and later Mars' Ring of Iron and the orbital shipyards of Saturn, under the scrutiny of the Emperor and the Forge-wrights of the Mechanicum, and indeed it was only that in alliance with Mars that the trans-solar expansion was possible in any meaningful way.
This was further aided when at last the Saturnyne Dominion, with its accomplished ship-masters, joined the Imperium after their alien overlords were overthrown, and as the Imperium expanded, many more great orbital shipyards were added: Voss, Grulgarod, Lorin and Cypra Mundi, all grew to near rival Mars itself in voidship production.
Driven by the will of the Emperor, the first expeditionary fleets pushed outwards into the galaxy. Preceding each great expeditionary fleet of hundreds, sometimes thousands, of vessels often ranged smaller contingents of independent flotillas led by a class of martial leader that would become known as the Rogue Traders Militant. Many of these individuals were former rulers of the numerous realms the Emperor had cast down first during the Unification Wars and later as the Great Crusade spread, formerly independent human worlds.
They were offered a stark choice -- bend their knee before the Emperor and swear service to the Great Crusade, or die by His hand. Though many set pride before what they regarded as slavery, others chose service and took up the Emperor's Warrant of Trade. There was a price, however.
The Rogue Traders Militant were expected to scout ahead of the leading edge of the Great Crusade, accompanied by their own armies as well as whatever assets had been ceded them by the Emperor. Operating so far ahead of the Emperor's crusading armies, the Rogue Traders Militant could expect little or no aid should they encounter foes too powerful for them to overcome.
After several solar decades penetrating the inky black of the void, Rogue Trader Militant fleets often appeared as ramshackle vagabonds, many of their starships taken from defeated enemies, sometimes including xenos vessels of entirely novel or esoteric form.
They were forbidden to return to Terra, for in His wisdom the Emperor sought not to just rid Himself of powerful rivals, but to ensure that even in their deaths they might serve Mankind. Many vanished alone and unheralded; slain, consumed or enslaved by nameless xenos abominations far from the light of Terra.
As the Imperium expanded, so too did its fleets. Countless long-lost wonders of technology were recovered, some wrested from the dead hands of unwilling custodians, and others surrendered willingly as fitting tribute to the Master of Mankind.
Some vessels were unique, constructed by methods even the most accomplished adepts of Mars could not hope to replicate: the Terminus Est, the Nicor, the Mirabilis and the Phalanx foremost among them. Other patterns and classes proved possible to reproduce and replicate, and before long the various arms of the Imperium's military acquired their own distinctive panoply of warships.
Those of the Legiones Astartes were often blunt of prow and slab-armoured, built to endure the withering storm of fire that accompanies a planetary invasion, their plasma furnace-hearts powering some of the most destructive weapons known to Mankind. But beyond these practical needs, each fleet favoured the nature of its Legion, from the sable black marauders of the Raven Guard to the baroque crimson and gold battlecruisers of the Blood Angels to the brute functionality and unadorned steel of the Iron Warriors' siege-barques.
The ships of the Emperor's wider naval armadas, the future Imperial Navy, were more diverse affairs, built for void supremacy. They ranged from stately battleships, multi-kilometre long engines of doom, their armour concentrated to the fore and their flanks repleted with rank upon rank of broadside batteries, to lithe and deadly destroyers and stripped-bare Warp Runners, to watchful piquet frigates and lumbering star-fortresses.
Beyond these were innumerable classes of transports, arks, conveyers and supply ships, the forge vessels of the Mechanicum and their own strange space-going engines of war.
As the terrible extent of the Warmaster Horus' treachery unfolded, other disturbing characteristics revealed themselves slowly amid the vessels under the Traitors' command. Fell runes appeared upon the flanks of the Warmaster's voidships and the barrels of their cannon were mutated or re-forged into gaping, fanged mouths. Viewports flickered with the fiery glimmer of the beyond and the once true and solid forms became twisted into hideous mockeries of respected and familiar classes.
As both sides girded themselves for full-scale war after the terrifying events of the Drop Site Massacre of Istvaan V, so the centres of production each controlled increased output exponentially. Demand was insatiable, and while the Emperor had once overseen the creation of the Imperium's fleets according to His own all-encompassing vision, following His return to Terra such matters were turned over to others.
The Council of Terra made ever more strident demands on the Forge Worlds of the Mechanicum as the awful scope of the coming civil war became clear. To make matters worse, many Forge Worlds declared for the Warmaster, while Imperial assets and materiel were co-opted or plundered for the armouries of the Traitor Legions. Both sides had pressed into service every class of vessel at their disposal, from mighty and unique relics of the Dark Age of Technology to the newly-produced and often all but untested scions of newly established Forge Worlds.
Before long, those warships unsuited to total war would be reduced to void-drifting nebulae of super-heated vapour and broken hulks, the tombs of all aboard, while those that survived would go on to fight in the greatest battles of the Horus Heresy and forge legends both bloody and glorious in their own right.
Throughout the seven brutal standard years of the terrible Imperial civil war that was the Horus Heresy after the Drop Site Massacre, both Traitor and Loyalist fleets clashed repeatedly in numerous long-running void battles, many of which still echo down the ages of history: the Battle of Phall, the Thramas Crusade and the epic final battle of the rebellion, the Siege of Terra.
Horus fell at last at the hands of his father, as the Emperor vanquished His traitorous son after confronting him aboard the Traitors' flagship Vengeful Spirit. The surviving Traitors broke orbit over Terra and fought their way free of the battle and escaped into the void. A time of reprisal and retribution known as the Great Scouring followed, and countless worlds were put to death by the Loyalists for siding with Horus, their corpses left as a warning to others.
Those Traitor Legions that remained in the Imperium were hunted mercilessly and hounded across the stars by pitiless Loyalists. The Traitors took refuge in the Eye of Terror, choosing to plunge into that maelstrom of madness rather than face extinction at the hands of the Emperor's vengeful warriors.
Shape of Change
Just as the Dark Gods of Chaos visit their warped and twisted blessings upon those of their followers who prove themselves worthy, so too do their "gifts" fall upon the great and aged machines devoted to them. A voidship's form, its very material essence, may be warped by the touch of Chaos to take on a shape ever more pleasing to its patron.
So it is that a starship might come to truly bear the mark of its patron god. It is not merely the will of a Chaos God that can alter a ship. A dedicated and worshipful crew will lavish much time on their vessel, reshaping it in their god's preferred image.
They will brand great heretical runes all across it, covering it in colours, symbols, substances or geometries favoured by their divine patron as testament to their fervoured devotion.
By foul enchantments and dark rituals, daemons, spirits and other Chaos entities likewise in the service of their patron may be summoned up, or even granted whole areas of the ship, invited to dwell within its engines, sustained in the material realm by the same bound psykers and Warp-Drive engines that once allowed the ship safe passage through the Immaterium.
Alone amongst the material creations of Mankind, these magnificent starships are designed to travel both the material and the immaterial, and so offer a sanctuary to daemons which cannot be found elsewhere.
These beings of Chaos might slumber within a warship's guns, launching fire from them with an unnatural fury; sweep formlessly throughout the ship's decks like a wailing ghost, driving off would-be boarders; or even lurk deep within the hull of the vessel itself, binding their own ancient malice with the intangible and resolute will of the aged machine, birthing a vessel with a true heart of Chaos.
Chariots of Slaughter - The Fleets of Khorne
To all but the blindest and most deranged of Khorne's followers, the need for ships to transport them across the stars is obvious, though beyond such cold utility even the most ancient of vessels deserves little more reverance. To Khorne's followers, such vessels are nothing more than steeds, chariots even, to take them to new fields of slaughter.
Where other gods might visit their blessing equally upon their followers and their machines, Khorne cares little for the beasts of steel, and it is instead upon the deranged and bloodthirsty warriors that slay in his name that Khorne’s blessing falls. Khorne's lust for blood eschews as cowardly and unworthy the long-ranged weapons of many Traitor vessels.
Even a perfectly well-armed and equipped warship of Khorne may forgo all weapons fire as its frenzied crew plough furiously forwards, impatient to fall upon their enemy in hand-to-hand combat within the narrow confines of the enemy vessel. With little love of psychic sorcery or arcane technology, followers of Khorne are often equally loathe to rely upon such tricks as teleportation and instead enact the will of the Blood God with their frenzied boarding actions.
So insanely devoured by the lust for blood are some that they forsake any form of ranged warfare entirely, and instead populate drifting Space Hulks, from where they can fall upon enemy fleets, or even worlds, in an unstoppable tide of boarding actions or bloody planetary assault. Khorne is not blind to the need for firepower, though he gives no favour to it, and his fleets remain rigidly utilitarian in this regard, willing only to utilise those weapons and those tactics which will ultimately bring them closer to their target, closer to the slaughter.
Floating Palaces of Slaanesh
Those vessels favoured by Slaanesh are nothing short of palatial -- the finest and most delicately crafted of galleons, carefully maintained and lovingly restored, their every inch bedecked in the most precious metals and glittering gems, smothered in the richest and most extravagant of dressings, details and iconography, decorated with the most exquisite portraiture, sculpture and art, invariably portraying acts of extreme perversity and artistic horror.
Within the followers of Slaanesh slumbers a malaise of ecstacy, drawing themselves into action only to further their exhausting pursuit of pleasure and new sensations.
Such are the delights within that these palaces of Slaanesh are as beacons of seduction to those that look upon them. Vessels nearing them might find their Vox-links bombarded not by the expected hails of identification, allegiance and intent, but rather by a cacophony of giggles, screams, moans and gasps, both disorienting and enchanting, broadcast by the fickle followers of Slaanesh, seemingly uncaring, perhaps even unknowing. For those whose inadvertent frequency scanning or attempts at communication open up such a channel, it is a voyeuristic gaze at pleasure beyond comprehension and an aural enticement that would bring the weak to their knees.
But pain is pleasure also, as the incautious should not forget. To turn their guns upon the entranced crews of nearby ships is as much ecstacy to the followers of Slaanesh as it is agony to their victims.
To board their vessels and take what captives may be found for purposes that may not be spoken is, to Slaanesh, not remotely a betrayal of the apparently harmless sensation which first proved so alluring to those same unwary victims. Such is the fate of any fool enough to stray close to the screaming Palaces of Pleasure which are the vessels of Slaanesh.
Beasts of Tzeentch
Alone amongst the Dark Gods, Tzeentch cares little to bring the starfaring vessels of Mankind under his service. The Warp is as much home to these vessels as the material universe, for they must travel through it at great length, and at greater peril, and cunning Tzeentch knows that it is within the Immaterium that his true power lies.
Within the Warp exist countless writhing entities, beasts of the Warp, born there or forged there by powers unspeakable. It is Tzeentch's great gambit that in his service these beasts are changed into the forms by which Mankind might know and fear them most -- great, hungry leviathans and all consuming serpents are the pets of Tzeentch, creatures born from the hellish depths Mankind has conceived of since first his eyes gazed out upon the great oceans of Terra and knew that something truly terrible must lie beneath. That humanity's own origins and birth lie also in such murky waters only adds to the instinctive dread and insurmountable fear such monstrosities awaken.
When his power is at its greatest, and when his loyal followers offer conduit and sacrifice enough that it might travel beyond the Immaterium, Tzeentch sends such beasts forth into the material universe itself, riding upon the tides of Chaos which surround the warfleets of the Ruinous Powers, buoyed along by the surging waves of sorcery and eddies of unreality which Tzeentch's followers bring in their wake.
Given form for a time, these leviathans fall upon Tzeentch's enemies like great predators, rending metal, flesh and soul apart with equal ease. The only mercy, perhaps, of such horrors is the inescapable impermanence of such Warp-spawned nightmares.
Plaguefleets of Nurgle
These so-called "Plaguefleets" comprise ancient, Horus Heresy-era battleships, stolen Imperial warships, and even space hulks gathered from the tides of the Warp. It falls to the warriors of the 6th Plague Company, the Ferrymen, to master and garrison these voidcraft, and to liberate new starships that may be added to the Death Guard's rotting armada.
The Plague Fleets are vital to the Daemon Primarch Mortarion's sons, for they are the vector by which the Death Guard spread Nurgle's blessings to the wider galaxy. Embarking onto these craft, the Plague Companies of the Death Guard ride the tides of the Warp like wind-blown contagion, emerging into realspace wherever Nurgle wills.
While their craft plough through the Immaterium, they fill up with thick clouds of revolting, fat-bodied plague flies that hatch from walls and bulkheads. When the Death Guard land upon enemy worlds or board their victims' spacecraft, these seething fly-storms come with them, spreading infection wherever they go.
Should ships of the Plague Fleets be lost or abandoned, they eventually find their way back to the Plague Planet as drifting derelicts to be crewed again. Some believe this is the will of Nurgle. Others claim that once a ship joins the Plague Fleets, its corrupted Machine Spirit is cursed to obey Mortarion until the end of time.
Additionally, starships whose crews met their end through disease and decay are the most pleasing sacrifices to Nurgle. Ships are cramped, claustrophobic places at the best of times, and the air which feeds their living crews is a commodity that must be endlessly recycled and filtered back into the vessel. Such lifeless air as this often becomes stale, and the stench of sweat and grime hangs heavy in it.
Under this mask of filth, Nurgle and his dedicated followers find little difficulty in spreading something rather more virulent throughout a vessel. Such plagues aboard ships are not uncommon and Nurgle laughs gleefully at such works.
A ship's entire crew may weaken beneath this malady, and in such desperation they will turn to Nurgle for protection -- and so a new Plagueship is born, its crew spared the sorrow of death, but instead gifted an eternity beset by the same plague which first laid them low.
But decay does not affect merely the living. Nurgle beams all the more proudly to see the creations of mortals broken down by decay. The most virulent of his ills do not only strike at flesh, but also bring with them a noxious, stinging acidic feel to the air which can sicken even the metal of a warship.
Like the bloated and pocked carcasses of his human followers, Nurglite Plagueships bear these scars of decay like a badge of worship -- liquified rust running like blood across the hull of his Plagueships, cankered and broken power supplies, plasma coils and radiation conduits seeping their magmas like pus. Such decay defines the vessels whose crews serve the Plague Lord.
- Codex Heretic Astartes - Death Guard (8th Edition), pg. 11
- Battlefleet Gothic: The Powers of Chaos, Chaos Fleets in Battlefleet Gothic, pp. 5-9
- The Horus Heresy - Book Two: Massacre (Forge World Series) by Alan Bligh, pg. 16
- The Horus Heresy - Book Four: Conquest (Forge World Series) by Alan Bligh, pg. 55