Screenshot #5 is the manually-operated sentry turret footage I was referring to earlier, there must be a significant reason though why the player would feel inclined to use the turret themselves rather than providing supporting rifle fire for the automated turret. Perhaps when AI-controlled, its rate of fire is slower or it must 'lock on' to a target before firing?
@SpaceMarines: I've never read the books myself but I've heard good things. I started with Fire Warrior on the PS2, then moved to the Dawn of War RTS PC games, and a good few months ago I joined the Ultramarines Chapter (clan) for Warhammer 40K Space Marine on the PS3.