Battlefleet Corona is a vast fleet of Imperial Navy vessels charged with the the protection of the vitally important Belis Corona Sub-Sector within the Segmentum Obscurus. Battlefleet Corona forms a component part of the Bastion Fleets which make up the massive Battlefleet Obscurus, as do its neighbours, Battlefleets Cadia, Agripinaa, and Scarus, as well as the more distant Battlefleets Gothic, Tamahl and Odessa, among others. Located near the Eye of Terror, this Imperial Battlefleet must maintain constant vigilance against the Forces of Chaos and the dreaded Black Crusades led by the Warmaster Abaddon the Despoiler.
The Segmentum Obscurus, also known as the Segmentum Obscura, is the region of Imperial space to the galactic north of Terra. This Segmentum of the Imperium of Man is the home of the vast Warp Storm and Warp Rift called the Eye of Terror, the primary home for the Forces of Chaos in the Milky Way Galaxy. The Imperial Navy's Segmentum fleet headquarters is located on Cypra Mundi, which also serves as the central headquarters of the Imperial military's Segmentum Command. The Segmentum Obscurus is the area of the Imperium most often under deadly threat by attacks from the Eye of Terror and is also the site for all of Abaddon the Despoiler's Black Crusades. As such, it currently is home to the majority of the Imperium's armed forces, which were most recently mobilised to a state of readiness not seen since the Horus Heresy as a result of the 13th Black Crusade in 999.M41.
The constant turmoil surrounding the Cadian Gate requires the fleets of Battlefleet Obscurus to be far more active than many other Segmentum battlefleets. The whole sector exists in an almost perpetual state of readiness, and as such the demands on manpower and resources are huge. Vast numbers of new, inexperienced ratings frequently have to be drawn up to replace those lost in the constant fighting. However, those that survive the harsh first years of military service around the Cadian Gate rapidly mature to become some of the most capable leaders in the Imperium. As with all highly militarised zones, it is important for the Imperial Navy to maintain substantial reserves of vessels around the Eye of Terror, ready to deploy as reinforcements should the need arise. Whilst it is possible to keep the vessels themselves ready in this manner, Battlefleet Obscura simply does not possess the manpower to keep reserve crews stationed aboard these vessels as well. Instead, whole orbital shipyards are filled with rows of silent, inactive vessels, often representing classes of warship now outdated or scarce.
In times of great need, these ships will be brought into service and crewed with ratings from destroyed or crippled vessels or even with hastily mustered new recruits, meaning the crew is unlikely to have any familiarity with their new vessel. A posting to such a reserve fleet is thus considered an unnerving duty, forcing a rating to enter deep into an unfamiliar vessel which may have lain dormant for centuries. Much superstition surrounds such fleets and perhaps because of this, unusual behaviour of both crew and vessel is rather commonplace. Reserve fleets are used only reluctantly by the Imperial Navy, and only in the most desperate of circumstances, but an invasion the size of Abaddon's 13th Black Crusade without doubt qualifies as exactly that -- the most dire of circumstances, the most desperate of times.
In a reserve fleet, all vessels are prone to certain unexpected events, such as mass panic or even mutiny amongst the crew, inexplicable noises, sensor readings and sightings or disconcerting setbacks and failure of machinery. Against Chaos fleets, where the followers of the Dark Gods are able to exert their influence to further unsettle their already nervous opponents, unforeseen events can be even more devastating.
Belis Corona Sub-Sector
The Belis Corona Sub-sector is one of the closest sub-sectors to the vitally important Fortress World of Cadia and the Cadian Gate, the only predictably stable Warp route that leads out of the Eye of Terror and into the realm of the Imperium. The Imperial Navy shipyards for the sector are located on the Forge World of Belis Corona. Belis Corona is a vitally important Imperial Dead World which serves as the Segmentum Obscurus' primary base for the Imperial Navy's Battlefleet Obscurus as well as essentially the Imperium's administrative capital for the entire Segmentum. There is a vast conglomeration of orbital dockyards in geosynchronous orbit about Belis Corona where entire sector battlefleets can be serviced and refitted. Massive stockpiles of munitions, supplies and other war materiel are stored in armoured bunkers buried many kilometres below the planet's barren surface.
2nd Black Crusade
As part of the 2nd Black Crusade launched in 587.M32, Abaddon wove a terrible hex upon a number of worlds close to the Eye of Terror, seeding them with the taint of the Dark Gods. Leading a small band of his elite warriors from the Black Legion, Abaddon breached the Imperial Navy base at Belis Corona. While his fleet launched a diversionary attack against the orbital shipyards, Abaddon and his Bringers of Despair, the strongest and most vicious members of the Black Legion's Terminator elite, landed on one of the system's outermost moons. Slaughtering the garrison, Abaddon crafted a complex sorcerous ritual using their mangled remains and invoking a curse that would sink deep into the core of the moon. Only centuries later would the curse awaken at the Despoiler's behest and do its terrible work, unleashing a mutagenic plague upon the Imperial defenders stationed there. By the time Battlefleet Corona had mustered to repel the attacks on the core worlds of the Belis Corona Sector, Abaddon had already departed, his mission complete.
Shortly after the assault on the shipyards of Belis Corona, an attack occurred on the Inquisitorial vaults of the world of Nemesis Tessera. Hidden beneath layers of ice and snow, the Inquisition had constructed a watch station from which to study the Eye of Terror along with hexagramatically warded cells to hold daemonic prisoners. It remains unknown if this was the work of Abaddon, but in a swift and brutal assault, one of the cells deep beneath the station was opened and the daemon contained within was released. By the time Inquisitorial forces had secured the facility, the attackers were gone, leaving only a trail of smoking corpses and spent Bolt shells to mark their passage.
13th Black Crusade
In 999.M41, war came without warning to the Belis Corona Sub-sector, and the opening moves by the Forces of Chaos saw large number of plague-ridden Space Hulks entering Imperial space. Though many were intercepted by the Space Marines and destroyed, some managed to escape the Astartes' attention. Some of these foul vessels of contagion found their way into the Belis Corona Sector, spreading their disease and pestilence amongst the masses throughout the sector. Along with the adjacent Agripinaa Sector, they were some of the first to bear witness to the rise of hordes of infectious, undead zombies that threatened billions of people on many of the Imperial worlds within the sector. This plague was later named the Curse of Unbelief.
While the defence of the Cadian Gate from the Forces of Chaos continued to go badly upon the surface of many worlds in the Cadian System, in particular Saint Josmane's Hope and Solar Mariatus, the war in space was fought more on the Imperium's terms. The Cadian System had been the focus of Abaddon's primary fleet actions, and the Imperium's fortunes there changed from day to day. The situation was highly fluid and the Chaotic naval forces found themselves stretched to exploit the victories they had won.
A fleet the size of which has not been seen since the end of the Gothic War eight standard centuries earlier had been dispatched from Cypra Mundi, and arrived at Belis Corona in preparation for a massive Imperial counter-offensive into the Cadian Gate. The arrival of this vast armada allowed those Imperial vessels that had been fighting continuously since the beginning of the invasion a brief respite. Severely depleted ship’s companies were bolstered through indiscriminate press-ganging, and hasty repairs and refits were undertaken on those vessels most in need of them.
The Imperial reinforcements were split into battlegroups, each tasked with bolstering the defences in a specific sector of the Segmentum Obscurus. The regions around the Eye of Terror encompass many millions of cubic light years, and only by the concentrated application of resources in those areas in most desperate need could the Imperial Navy hope to make inroads and slow, stall, and eventually repel the Chaos warfleets plaguing the region. A small number of Imperial Navy ships won a decisive victory when they managed to hold back a larger Chaos Fleet at the Ilthirium Belt, buying time for Battlefleet Agripinaa to arrive and allow the remaining ships to retreat. This course of action however, left the Agripinaa Sector open to invasion and soon the worlds of this sector and the Belis Corona Sub-sector was transformed into nightmarish realms of plague and pestilence.
Upon arriving at the Cadian Gate, the Doom Eagles Space Marine Chapter dispatched forces to a number of warzones, notably areas that had already suffered terribly at the hands of the Forces of Chaos. The largest of these detachments, under the command of Captain Luctus of the 3rd Company, was involved in operations within the Belis Corona Sub-sector, where the notoriously pious Chapter battled those who had fallen to the Curse of Unbelief. Only those without the strength of faith to resist were afflicted by the Zombie Plague, and it has been noted that not a single Doom Eagles Battle-Brother was affected by its blight. The Doom Eagles proved effective in combating the Plague Zombies infesting many worlds of the sub-sector, though, typically for this aloof Chapter, they had refused all offers of support in consolidating these successes.
The Cadian Sector High Command was also briefed by the Ordo Xenos on a number of other factions which assailed Mankind as the Forces of Chaos battered at the doors of the Cadian Gate. The Inquisition warned the Cadian High Command to be alert for seemingly incongruous reports of alien infiltrations in the region near the Subiaco Diablo System, particularly for attacks coming up from below the galactic plane. They would not expound further on what they meant by this, but insisted that the Cadian High Command should inform the Inquisition immediately should any such attacks by unknown xenos materialise. Despite being beset on all sides, the Imperial forces and their commanders remained imbued with a sense of righteous indignation. If every damned creature in the galaxy was now ranged against them, then they were determined to take them all into oblivion with the last cry of the human race.
The Imperial forces largely held at Belis Corona, the location of the greatest orbital shipyard of the Imperium, which suffered the worst excesses of a Tyranid splinter Hive Fleet, and the horrific plagues bestowed upon its hive cities by the Death Guard Traitor Legion. At the height of the invasion, something truly unexpected occurred. Defenders in the outlying star systems reported contact with Tyranid organisms -- at first individual vanguard-organisms such as Lictors, but soon entire broods of Genestealers and Hormagaunts. A splinter fleet of Hive Fleet Leviathan, a Tyranid fleet known to be attacking up through the galactic plane, was taking advantage of the mass destruction initiated by the Chaotic invasion to gain a foothold in strategically vital Imperial space. Faced with both the pestulant forces of the Death Guard, and the voracious hordes of Tyranids who were, unlike the human defenders, immune to the Plague God's blessings, the forces of the Imperium were hard-pressed to defend the vital worlds of the Belis Corona Sector. It was the intervention of the forces of the Eldar of the Ulthwé Craftworld and then the orbital bombardment of Laurentix that allowed the forces of the Imperium to fight back, despite the disastrous ambush of forward elements of Battlefleet Solar at the Bairsten Prime Warp jump point. Subiaco Diablo saw the Convent of the Order of the Ermine Mantle hold out against overwhelming odds, though at terrible cost, before being relieved by a host of Adepta Sororitas units drawn from across the region, thanks to the leadership of the renowned Canoness Astra.
Battlefleet Corona Fleet Composition
At the time of the 13th Black Crusade, Battlefleet Corona consisted of the following vessels that took part in the valiant Imperial defence:
- 7 Battleships
- 13 Cruiser Squadrons
- 17 Escort Squadrons
- Battlefleet Gothic Armada, pg. 28
- Black Legion: A Codex Chaos Space Marines Supplement (Digital Edition), pp. 31-32
- Codex: Eye of Terror (3rd Edition), pp. 16, 25
- Thirteenth Black Crusade (Sourcebook) by Andy Hoare