In most modern armies, you either join as an officer, who are generally more educated and paid more, or as an enlisted, who are more of the workling class blokes, who get paid less. Sometimes if you're enlisted long enough, and you show potential, you're promoted to a sergeant, and if you're lucky or talented, you're even promoted into being an officer.
Both, the Office line, and the Enlisted line start at rank 1 (E1: private, airman basic, seaman recruit. O1: second lieutenant, Ensign), and are promoted rank 2 (E2 or O2) and then rank 3 and so on. But the point is, the officer line and the enlisted line are usually pretty destinct, and their cultures don't always intersect.
So, where exactly in this system do the officers lay? They would make perfect sense as specialists, I guess. Or you could turn the sergeant into an Officer instead. Give him extra comrades, and RP precedence. This also fixes the problem of "well, how does my heavy gunner progress in his career?"