The Obstinate Marines have a unique method of war. Their entire existence is dedicated to attack. Lighter and faster troops and vehicles arrive first, sowing destruction and confusion, pushing past the front line into the enemy rear to continue raiding and marking resources caches. While the enemy scrambles to deal with the sudden overrun, the main forces appears on the horizon as a massive cloud of dust that blots out the sun. Battle brothers, terminators, dreadnaughts and heavy armor units slam into the disorganized front like a tidal wave hitting a marina. Casualties are ignored, those who run out of ammo simply abandon weapons on the spot and grab anything they can to continue their march. As this wave of death rolls over the enemy, the massive titan forges and rolling factories the size of small cities appear. These are tended by teeming multitudes of servitors and tech marines, who salvage fallen soldiers, vehicles, resources, raw ores are harvested from the bleeding earth by massive mining servitor units the size of warehouses. Noxious fumes from gargantuan war forges choke and cloud the skies as a five mile wide tide of mobile industry consumes all in it's path. They take weeks to pass, from the first scout to the last scrap-servitor, and all that is left in their wake is scorched, blasted dirt that has been churned into a bog slickened by the blood of those foolish enough to try and stop their march.