very Space Marine Chapter that adheres to Roboute Guiliman's great organizational tome, the Codex Astartes, maintains a number of companies designated as "Battle Companies." These comprise six Tactical Squads, two Assault Squads and two Devastator Squads — a hundred Space Marines. The Battle Companies form the main battle lines and generally bear the brunt of the fighting. A single Battle Company acts as the core of an army that may be accompanied by elements from the Veteran, Scout and Reserve Companies, as well as armoured units from the Chapter's Armoury.

Battle Companies are deployed to meet full-scale threats that the Imperial Guard cannot counter. They are transported by Strike Cruisers, which remain in orbit to support the attack. The company is led from the front by one of the most able commanders the Chapter can field and will achieve its mission no matter the odds, holding its objective against every counter-attack. A Battle Company can defeat an enemy army 10 times its size, bring a rebellious world back under the rule of the Imperium, or besiege an entire alien city. Such is the breadth of their skill that there is little in the field of war they cannot achieve.