The Troop Carrier armadas, some of which took hours to pass a given point, formed a rather unstable platform from which paratroopers jumped and gliders released into enemy territory only a few hundred feet below. Initially, aircrews flew these operations at night, in tight formations, unarmed, all navigation lights off, no self-sealing fuel tanks. They delivered their human payloads from low altitudes at slow airspeeds, and were vulnerable not only to flak but to small arms fire. Indeed, TC airmen were the only Air Force flight crews for whom infantry helmets were required flight gear.
In contrast, modern warfare uses smart bombs and missile technology, helicopters for air landing, satellite-based navigational aids, smart weapons for covering fire, and many other advances that make the delivery of invasion spearheads much less manual, and not so costly in American lives. In World War II, this was not the case.
The delivery technology of that era was primitive. Pilots looked out cockpit windows to identify landmarks in the light of a partial moon, and used imprecise navigational technology, like Rebecca-Eureka and Gee, to help confirm positions determined by pilotage and dead reckoning. Airborne troopers did not "deliver" the spearheads, they were the spearheads, and Troop Carrier units delivered them. Communications between ground and air—so vital for air supply of airborne troopers before they linked up with ground units—was poor to non-existent until the spring of 1945.