At the risk of over-simplification, most officers are not on the gun line as you call it, although gun position is more correct. A regular field regiment has two gun batteries, a STA battery (for locating enemy artillery and finding other stuff,) a FOO battery that provides all the observers for the regiment and a headquarters battery, along with a regimental headquarters. There are four gun troops, each with two officers in the rank of 2nd lieutenant to captain. The other thirty-plus are doing other things, from commanding STA organizations to providing observation, liaison and fire support coordination at all levels from combat team to brigade headquarters, and of course some are involved in administration.