If he wants an assurance that he will never have to fire a weapon in anger he will have to elist as a concious objector (or choose the airforce).
The armed services always reserve the right to move people into fields where there is a need from other fields, and enlistment "promises" are best efforts only. When foot soliders are in high demand and mechanics are a dime a dozen all bets are off.
He is comfortable around guns but until you are in the situation you never know. We have lots of family who have served in the military and the experiences have left an impression on them the rest of their lives (not always good).
If he wants an assurance that he will never have to fire a weapon in anger he will have to elist as a concious objector (or choose the airforce).
So the Air Force doesn't have to shoot huh? Which Air Force are you referring to?