- "Through multiple campaigns and hardships, against Daemons, Xenos and other enemies of the Imperium, I have learned to only trust myself, and the Emperor."
- —Crycer Duron, Chapter Master of the Grandmarines.
The Grandmarines are an 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.
The Grandmarines were formed in the 8th Founding, or the 34th Millennium, originally lead by Norias Tydon, and currently lead by Mephideus Manularis.
The Purge of Growver
The Purge of Growver, was the great purge of the entire Growver Sector, Chaos Cults, stray Ork Warbands, and even ancient Necrons, fell to the Grandmarines, this purge, started the troubled and secretive history of the Grandmarines.
Troubles with the Inquisition
Battle of Velanor
The Grandmarines received a transmission from the Governor of the Velanor. Eight regiments of the Velanoran Grenadier Guard had gone missing. Chapter Master Mephideus sent the 2nd, 4th and 5th Companies, under the command of Captains Grimmarus Tybus and Adronus Cadellion to investigate the situation.