Battlefleet Gothic - 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 wider Belis Corona Sector, spreading their disease and pestilence amongst the masses throughout the sector. Along with the people of 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 Belis Corona 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.Lord Admiral Quarren, the commander of Imperial Navy assets in the Cadian System, had succeeded time and time again in defeating Chaos warfleets many times the size of his own, allowing reinforcements to enter the fray around the Fortress Worlds of the Cadian System. At the same time, a massive influx of reinforcements in the Scelus System of the Cadian Sector had penetrated the Chaos blockade of ships and minefields, and in the Belis Corona System of the Belis Corona Sub-sector the entirety of Battlefleet Gothic had stormed into the fray. Infernal mines sewn across the battlefront accounted for the destruction of only a few vessels in the fleet, and now Battlefleet Gothic had the opportunity to avenge the losses it had suffered in the Gothic War at the hands of Abaddon the Despoiler's own warfleet. If the relentless momentum of the invasion could be slowed for just a short time, then the defenders on the ground would have a real chance of victory. The Imperial Navy had gambled all on this sector-wide retaliation and should it fail, then Battlefleet Obscurus would be so weakened that only the redeployment of fleets across the whole Imperium would hold any hope of holding back the Despoiler's invasion.The Imperial Navy fought with courage and vigour throughout the long campaign, ruthlessly taking the battle to the enemy wherever it encountered them. Lord Admiral Quarren was hailed a true hero of the Imperium, for his masterful defence of the space lanes was all that stood between survival, and utter defeat for the Imperium. Though Cadia remained besieged at the end of the campaign's formal operations, the Imperial Navy commanded space, and was able to offer support to beleaguered Imperial forces on the ground. The only question was whether the rapid redeployment of almost the entirety of Battlefleet Gothic, along with a substantial proportion of Battlefleet Solar, would leave the Navy dangerously overstretched elsewhere and unable to maintain the level of operations required to hold the line at the Cadian Gate.