This was a background theory I was thinking of doing, maybe as a RPG thing or an army idea...
Let's say there's a Astartes chapter on a high-population world. They have a good sized PDF and can recruit their marines at a fairly good rate but one day the chapter master figures out that he's missing out on recruiting half the good warriors out there-the women. So he decides to "sponsor" (via providing equipment and facilities) a minor Adepta Sororitas order (a new one, not an existing one) in the same system. The theory is that they could accompany the marines (the PDF can't) on some battles or could be asked to go alone if there's a situation in a nearby system and the chapter doesn't feel it needs their attention.
The Good:
Both have a solid backup
The "talent" doesn't go to waste in fighting the enemies of the Imperium
A chance to model matching power armor in 2 very different armies
The Bad:
Who is really in charge? The sisters would hate having a marine chapter master bossing them around.
The Ecclesiarchy would probably have a problem with it.
There's the religious differences of the 2 groups.
So does any of this work? Or make sense? Or is...HERESY?