Your right it only works when you are in the core and not in a cam (might be a bug actually)I believe you just have to Rotate the Weapon Computer to face the direction you want them to fire, and you must be in the core of the ship (not in a cockpit view).
Pretty sure it's in this version, since I have heard of Vertical firing Missiles that Arc on ships (Missile+Beam > Computer pointed up) o -o