Up until now, it has been Army, Coast Guard, Navy, Marines and Air Force. This is nice and symmetrical since there are five sides to the Pentagon and five stars in the highest possible general rank. The addition of another branch breaks this symmetry, though. So, what to do?
I propose that the Marines be subsumed by the Department of the Navy since they are naturally part of that branch. The symmetry is thus restored. The branches of the Military, then, will be the Army and it's Four Bitches as it has been and as it always should be.