Sagan Sub-sector

The Sagan Sub-sector is a region of space that is a Sub-sector of the Badab Sector located within the Maelstrom Zone of the Ultima Segmentum. It was an area of strategic importance during the Badab War and was fought over repeatedly by both the Imperial Loyalists and the Secessionist forces. The most important world within the Sagan Sub-sector was Sagan III.

History
When the Badab War began, the Sagan Sub-sector was firmly under the control of the mercantile lords of the adjacent Karthago Sector, which maintained a fleet anchorage for their naval forces above the world of Sagan III. But as soon as the conflict began, the Secessionist forces managed to drive the Karthans and their allies in the Fire Hawks Space Marine Chapter from the world, and claim the entire sub-sector as their own by the end of 904.M41. This state of affairs would remain in place until the Second Battle of Sagan erupted in 908.M41 with a very different outcome.

Second Battle of Sagan
The Second Battle of Sagan was a major planetary assault undertaken in 908.M41 during the Badab War that drove the Secessionists from their fortresses in the Sagan Sub-sector. The assault was carried out by the largest combined Loyalist force fielded to that point during the Badab War. This offensive utilised the massed strength of the Fire Angels, Red Scorpions and Exorcists Chapters supported by assault-specialised forces drawn from the Salamanders, Raptors and Novamarines. The Secessionists chose to mount a defence at any cost rather than giving up the strategically vital Sagan System. The fighting proved to be bloody and costly in the extreme. In a desperate attempt to either drive the Loyalists from the surface of Sagan III or render the planet unusable to them, the Astral Claws resorted to the use of viral weapons that slew tens of thousands of the world's population. This use of weapons of mass destruction ultimately destroyed a sizable component of the Secessionists' own battle line. The Fire Angels deployed their full Chapter strength and bore the brunt of the Loyalist casualties, valiantly sacrificing themselves in order to contain the Astral Claws' desperate final attempts to drive their foes from the world through the utilisation of suicide attacks. This campaign resulted in the highest death toll of any single engagement of the war to this point in the conflict as well as the loss of several key Secessionist warships in a vain counter-attack on the system.

The successful invasion of the Sagan System proved to be a major turning point of the war. After the system fell under Loyalist control it became the primary Imperial base in the Maelstrom Zone, affording the Loyalist offensive greater access to the primary stable Warp routes into the region while denying those routes to the enemy. Shortly afterward the end of the campaign, Sagan III was used as a supply point in order to fully relieve and reinforce Surngraad and support the start of the Endymion Suppression Campaign. This Loyalist advance effectively forced the remaining Mantis Warriors forces into a purely defensive posture, isolating them from the Badab Sector and their Secessionist allies. After the Second Battle of Sagan, the Maelstrom Zone was effectively split into two regions -- the Endymion Cluster and the still heavily defended Badab Sector itself. From this point onwards in the conflict, the Secessionists were only able to conduct commerce raids and targetted strikes which were carried out by the vessels of the Executioners and Lamenters Chapter fleets.

Beyond the difficulties posed to the Imperium by the ongoing Badab War, the safety of the Ultima Segmentum was also threatened at this time by massive Ork incursions after multiple WAAAGHS! erupted across the Eastern Fringe of the galaxy. With the Secessionists having been judged sufficiently contained after the victory at Sagan, the Loyalists redeployed the Chapters that had suffered battlefield attrition to some degree to deal with the Greenskin threat. This redeployment included the forces of the Novamarines, Raptors and Howling Griffons Chapters. They were withdrawn one-by-one from the conflict in managed stages as part of a major Imperium-wide strategic redeployment along with a number of warships of the Segmentum Solar reserve forces which had been deployed in support of the Loyalist cause.