Space Marines - Bonds of Brotherhood: A Space Marine has three levels of interaction that shapes who he is: the overall Chapter views and beliefs, the battle doctrine and mind-set of his company, and the individual bonds he forges with his squad-mates with whom he fights side-by-side.The Chapter - The first bond that all Space Marines share is the bond that makes them part of their Chapter. This is coded into their flesh through the gene-seed they all share, dating back to their primarch. Even Chapters of the subsequent Foundings share this trait, no matter how far they are removed from the lineage of their progenitor. The beliefs and combat doctrine of the Chapter for most is rooted in the Codex Astartes, the tome of tactics and strategy created by Roboute Guilliman after the Horus Heresy. It is at the Chapter level that the command structure, battle doctrine, and many inherent beliefs are created for the Space Marine. A member of the Space Wolves knows that it is his duty to take the battle to the foes of the Emperor directly, bringing death with sword and Bolter in close quarters. The same cannot be said of an Iron Hand, who favours dealing death from afar with master-crafted weaponry and war machines. The belief structure created by the Chapter becomes everything to the battle-brother. Many initiates come from Feudal or Feral Worlds, who know nothing of the Imperium and the greater universe, so it is through their indoctrination into the Chapter that everything they know of the galaxy is taught. If the Librarians and Chaplains of the Chapter teach these young men that they must entreat the Machine Spirits to make their Bolters fire and their starships traverse the void of space, many do not think any differently and this will become simple fact to the aspirant. Another Chapter will teach its brethren the intricate ways of maintaining their weaponry and how the Imperium actually works and functions. These wildly disparate views on the basic structures of the universe around them can lead to interesting interactions when Astartes of different Chapters must work together.The Company - Once an aspirant has become a Space Marine, he is placed into a company. At the company level, a Space Marine learns the deeper structure of how he will fight the enemies of Mankind. The Codex Astartes outlines the progression of each battle-brother through the companies of their Chapter and what skills he shall gain during his tenure in each. According to the Codex Astartes, a battle-brother progresses from a Scout Marine of the 10th Company, to a Devastator of the 9th Company, then on to an Assault Marine of the 8th Company. Once a Space Marine has mastered the many ways in which he is capable of making war, only then is he ready to enter the Tactical Squads of his Chapter's Battle and Reserve Companies. Space Marine companies often have many ancient traditions and rites based on their past battles and achievements. These become very important to the battle-brother and will greatly influence him. For example, a member of the Blood Ravens' 5th Company, who lost many of his brothers in a prolonged campaign against the Aeldari, may observe an annual rite commemorating the sacrifices made to bring about victory. Missing this observance -- if not in an active battle situation -- could bring about a sense of melancholy and shame to the battle-brother, who feels he is not properly honouring his fallen comrades.The Squad - The most intimate bonds are amongst the battle-brothers of the Space Marine's squad. Day in and day out, these hardened warriors fight alongside each other for the glory of the Emperor and the Imperium. With each battle, the members of the squad become more ingrained in the ways of battle and how to rely on each other in any circumstance. It is within a squad -- and that can be a battleline, close combat, fire support or Veteran squad -- that the Astartes has spent the most time. If he leaves his squad for another, to begin his tenure with the Deathwatch, or for some other reason, he must leave a part of himself behind, and learn how to function on a whole new level as part of a new team.