Airborne!

From a technology standpoint, Airborne! was a somewhat pioneering game as it was the first Mac game to use digitized sound (most notably for the symphonic rendition of "Ride of the Valkyries" during the opening screen), but gameplay-wise, it's essentially an adaptation of Paratrooper. You control a single person who, using both an antiaircraft gun and a mortar gun, must ward off waves of helicopters (and occasionally other aircraft) dropping paratroopers to come and blow up your gun station.