During the spring of 1951, high rates of insect-borne diseases such as malaria and dysentery alarmed Air Force and Army doctors in South Korea. The 315th Troop Carrier Wing responded with an aerial spray operation called Spray Gun. Between June and October, the 437th Troop Carrier Wing employed a pair of C–46 airplanes equipped with 850-gallon insecticide tanks and special spray equipment to cover thousands of acres in South Korea with DDT insecticide. Small Army L–5 liaison aircraft assisted the C–46s. The planes flew at low levels ranging from 50 to 100 feet over cities and military installations.
The insecticide sharply reduced swarms of mosquitoes, flies, lice, and ticks. Medical experts reported a decline in the incidence of insect-borne diseases. The onset of cold weather, which temporarily eliminated the insect problem, ended the first phase of Operation Spray Gun in October.
The project resumed in June 1952, with the 315th Troop Carrier Wing being replaced by the 437th Troop Carrier Wing, which took over its C–46 spray aircraft. Flying from Brady Field, Japan, the 315th Troop Carrier Wing planes sprayed South Korean cities and military installations with insecticide throughout the summer, returning over each target area every week or two. Four Air Force T–6 training aircraft replaced the L–5 Army planes used the previous year to help the two C–46s.
The 315th Troop Carrier Wing flew the third phase of the aerial spraying project in April and July to October 1953, using one C–46. During those five months, the plane flew 160 missions and sprayed 588,625 acres in South Korea.
In three years, Operation Spray Gun reduced dangerously high insect numbers and kept disease rates low. Some missions also helped to save forests threatened by pine borers.