The side-firing AC-47 gunship, a World War II transport fitted with side-firing electrically-driven machine guns aimed by means of a light-amplifying starlight scope, had proven highly successful in South Vietnam. These aircraft were sent over the Ho Chi Minh Trail and achieved some initial success, but then suffered heavy losses to radar-controlled AAA and had to be withdrawn in the summer of 1966. The problem was not the concept, but the AC-47's lack of electronic countermeasures and its limited performance and so the Air Force developed an advanced gunship based on the C-ISO four-engined turbo prop transport. The definitive version of this, the AC-130H, mounting a 105 mm howitzer plus 40 mm and 20 mm cannon, became the bane of truck drivers on the Trail. Fitted with an impressive array of devices for night work, including low-light-level television, infra-red sensors and a device which could detect the electrical emissions of truck spark plugs, the AC-130s achieved an impressive tally of trucks destroyed.
The struggle was a bitter one, with communist road repair crews, truck drivers and anti-aircraft gunners pitted against awesome aeria firepower that was directed by some of the most sophisticated reconnaissance, target-detection and fire-control systems ever seen. The value of air interdiction had long been a point of doctrinal dispute among the U.S. armed services, and its more extreme critics charge that the final outcome of the Vietnam war definitively discredited the concept. A more balanced view points to the enormous commitment made by North Vietnam in resources and manpower - as many as 10,000 workers died to keep the Ho ChiMinh Trail open - to maintain the flow of supplies south. Vo Nguyen Giap and his colleagues on the PAVN General Staff were thoroughly competent and realistic planners, who would not have made such a commitment had it not been vital. The final argument supporting the importance of the air interdiction effort lies in the ease with which the North Vietnamese built up their logistic stockpiles and troop concentrations for their final, victorious offensive in 1975. The contrast with 1972 is instructive.