A highly mobile, rapid strike force like G.I. Joe can't depend on slow, ponderous artillery to keep up with them. They need to bring their own fire-support with them in the form of a high-powered mortar, but a mortar man can only carry a limited number of shells, so he had better be able to make every shot count! DOWNTOWN can judge range and trajectory just by eyesight. If he knows where the target is, he can hit it!