US Marines
are a separate service branch anyway. (From Army/Navy/Air Force).
I presume the situation will play out similarly to the Air Force foundation you mention: all services will develop their own sub-branch, there will be arguments about who is best and who's stepping on who's toes, then there will be attempted take overs with attendant arguments, and finally a separate service will be established, to be looked down upon by the others.
Let's just hope that there aren't any major events needing the armed services attention in the interim whilst they're playing at politics (see: Clausewitz)