Now I know what the Airforce, the Army and the Navy all are and I do have read about a small bit about the Marines and know that there more or less assigned as a support unit to the Navy but what about there role in the SGC, is it just generally the same? Also who's in charge of the Marines overall, in the SGC itself? The reason I'm asking now is because I've been watching season 1 of Atlantis and although Shepherd is an Airforce Major, after Sumner (who is a Marine Colonel) gets killed, Shepherd is the one who is given command of the military personnel. I'm assuming as Ford is also Marine and a Lieutenant he would've been second in command so shouldn't would he have command over the Marines also? Does this sort of thing happen in the RL military where officers from one branch take command of units from another branch?