New to BFG

[Goochman]

Hello friends, I'm new to BFG and I have lots of questions but I'm shooting for one now.
I've read a lot of fluff and I was wondering, does Space Marines Fleets can only be assembled from their barges or can any Imperial ship be ( Commissioned ) by the Astares and call them theirs? You know , outside the Imperial Fleet Colors and regulations?

Remember the Fallen Brothers at Rynns

[afterimagedan]

Space marine fleets can adopt an imperial or chaos ship as a flagship. Allies are another option. In the space marine fleet list, there are rules for taking allies.

[Goochman]

Space marine fleets can adopt an imperial or chaos ship as a flagship. Allies are another option. In the space marine fleet list, there are rules for taking allies.
So I can do my fleet with the Battle Barges and regular Imperial Ships and just for fluff say that they are adopted?

Brother G

[The AKH]

The "Codex Astartes" fleetlist allows you to take Imperial Navy escorts as rapid strike vessels - your capital ships have to be all Battlebarges or Strike Cruisers.

I believe there's also an Armageddon War variant list that intermingles the Imperial Navy and Space Marine choices more.