Board Thread:Warhammer 40k General Discussion/@comment-3416287-20130528142310/@comment-3580035-20130604122550

Inquistion and Grey Knights are a special and rare case. They mindwiping also happens after the battle and has nothing to do with how they fight with IG.

Space Marines are used for surgical strikes and to perform tasks IG cannot. IG does the heavy lifting and fulfils most missions in a campaign. The Taros Campaign gives the most accurate protrayal of this. IG basically did the whole campaign, whilst the marines intervened at the start to take out orbital defence missile silos, allowed a breakthrough to occur on the main continent halfway through the campaign, and acted as a rearguard for retreating IG forces at the end.

How they work together though almost always depends enitirely on the situation and the nature of the chapters, so there is no real absolute method of cooperation.