Гм, вот что сказано в The Horus Heresy - Collected Visions про численность:
"There was no limit on the size of a Space Marine Legion and most of them could muster at least 100.000 combatants. The Ultramarines Legion was by far the largest, and its Primarch, Roboute Guilliman, could call upon the services of over 250.000 Space Marines."
А вот про организацию:
"The structure of a Space Marine army varied slightly from legion to Legion, but at the core of all of them was the company of one hundred fighting men led by a captain. Companies were usually grouped into battallons, normally five companies strong, and led by a lieutenant commander. Battalions are brigaded together in pairs, as a regiment of one thousand warriors. These were variously known as "regiments", "wings", "chapters' or "great companies"."
