The Grandmarines are and 8th Founding successor chapter of the Ultramarines, they police the Growver sector, in the Segmentum Ultima. Their homeworld is the primary planet in the sector, the Fortress World of Growver, which when they found it, was swarmed in Daemons, Xenos and other enemies of the Imperium, a great purge was held, cleansing the world of the filth that slept there. After purging the world, the Grandmarines purged the other planets in the sector, finding multiple Chaos Sorcerors and Chaos Champions hiding in the underbellys of the worlds.