After the resurrection of Guilliman in late [[M41]], he began to see many of the flaws that came from overly-strict adherence to the Codex Astartes. As a result, he has reformed much of the Codex and eliminated much of its restrictions on Space Marines. New additions include the addition of [[Primaris Space Marine]] formations such as [[Intercessor]], [[Aggressor]], [[Inceptor]], and [[Reiver]] Squads, as well as the inclusion of two [[Space Marine Lieutenant]]s below the Company Captain, each commanding a demi-Company. Furthermore, Squads in the Codex Astartes are now defined as '''[[Battleline Squad]]s''' ([[Tactical Squad|Tactical]] or [[Intercessor]]), '''[[Close Support Squad|Close Support]]''' ([[Assault Squad|Assault]], [[Reiver]], and [[Inceptor]]), or '''[[Fire Support Squad|Fire Support]]''' ([[Devastator]], [[Aggressor]], [[Eradicator]]s{{Fn|19}}, or [[Hellblaster]]). These formations exist alongside [[Space Marine Veteran|Veteran]] Squads, [[Scout]] Squads, and [[Vanguard Space Marine]] Squads.{{Fn|15}}

The 2nd, 3rd, 4th and 5th Companies are known as '''Battle Companies''', as they generally form the main battle force deployed for engagements. All four Companies have the same organisation, split into 6 '''[[Battleline Squad]]s''' which consist of [[Tactical Squad|Tactical]] and [[Intercessor Squad|Intercessor]] formations, 2 '''[[Close Combat Squad]]s''' which consist of [[Assault Squad|Assault]], [[Reiver Squad|Reiver]], and [[Inceptor Squad|Inceptor]] formations, and 2 '''[[Fire Support Squad]]s''' which consist of [[Devastator Squad|Devastator]], [[Hellblaster Squad|Hellblaster]], or [[Aggressor Squad|Aggressor]] formations. Each Battle Company also includes around two [[Dreadnought]]s, and maintains their own motor pool of [[Rhino]], [[Impulsor]]s, and [[Razorback]] transports, [[Land Speeder]]s , and [[Space Marine Bike]]s.{{Fn|5}}