Battlefleet Koronus

Battlefleet Koronus is a small fleet of Imperial Navy vessels charged with the the protection of the Koronus Expanse located in the Calixis Sector, an Imperial sector located in the Segmentum Obscurus on the northern edge of the known galaxy, near the Halo Stars and the Eye of Terror. To the trailing edge of the galaxy, the Calixis Sector is bordered by the hazardous territories of the Fydae Great Cloud and to spinward by the Scarus Sector.

History
Beyond the Rubycon II System, the Koronus Passage looms wide, ready to swallow the Rogue Trader ships that brave its depths. The Maw is so vast it is more a region of space than an opening in the Great Warp Storms along the Drusus Marches, but the Maw can also swell closed when the Warp Storms rage, shrinking to the narrowest passage. Though the boundaries of the Calixis Sector end at the entrance to the Maw, there are certain Imperial organisations that venture beyond those bounds. Chief amongst them is the Battlefleet Calixis of the Imperial Navy which maintains a watch of warships at Port Wander, the entrance to the Maw, and some say, within the Koronus Expanse beyond. This squadron, under command of Fleet-Captain Nathaniel Horne, is on extended detached duty from the rest of Battlefleet Calixis.

Established in 673.M40, the Imperial Navy squadron known as Passage Watch 27-Est, is not large, especially compared to Battlefleet Calixis as a whole. It is comprised of several Cruisers, Light Cruisers, and Battlecruisers, supported by multiple Destroyer and Frigate Escorts. These warships possess most of the combat experience in Battlefleet Calixis, as they are almost constantly in conflict with raiders, pirates, and the occasional xenos vessel that comes through the Maw to plunder the Calixis Sector. Passage Watch 27-Est is hard-pressed but vigilant, and on occasion has sent its distinctive grey-hulled, crimson-prowed vessels on counter-actions and reprisals into the Koronus Expanse. This has led the warships' crews to refer to themselves, only half-jokingly, as "Battlefleet Koronus." For more than 350 standard years, Passage Watch 27-Est has kept this vigil.