Shepard should be a major for the Marines. Not a Commander. This girl is so sexy.

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BTW I love the Ting Tings. In a manly type of way.
NO SHEPARD IS A TERRORIST/PIRATE!!! Looting the galaxy and peoples homeworlds of their precious resources. I'm kidding, but yeah much agree'd with Revenant. Do your homework people.
I don't really think there's specific forces like Army, Navy, Air Force, Marines and space equivalent of Coast Guard. But Shepard is probably in the Navy because he commands a ship.
Guys Stop arguing Shepard is Alliance Navy end of story. Bioware Confirmed he/she is Alliance Navy. Shepard is also a commander so dispute settled move on.