South Vietnam, had been sprayed at least once with herbicides (NAS, 1974). About 1.2 million acres, or roughly 34 percent of the sprayed area, was sprayed more than one time. These calculations are based on figures for the spraying missions by the C-123s and do not take into account unrecorded helicopter or ground sprays, or the effects of wind drift, aircraft speed, and rates of delivery. III Corps was the most heavily sprayed area of Vietnam, receiving about 53 percent of all herbicide sprays from 1965 to 1971 (Table 3-6). Thirty percent of III Corps was sprayed at least once (Westing, 1984). War Zones C and D, and the Iron Triangle in III Corps, can also be identified as heavily sprayed areas in maps of herbicide defoliation missions. The Rung Sat Special Zone in III Corps near Saigon, where the Saigon and Dong Nai Rivers linked together, was the most heavily sprayed region in Vietnam, as well as a site of frequent U.S. Navy operations. In 42 missions, the C-123s sprayed thousands of gallons of herbicides on the mangrove swamps to flush out Vietcong from hidden strongholds, from which they attacked supply ships and instituted offensives in the Delta region and surrounding provinces (Dux and Young, 1980). The area was sprayed consistently until 1970; the NAS (1974) estimated that 57 percent of the Rung Sat Special zone had been sprayed.

Another heavily sprayed area, the Ca Mau Peninsula at the southern tip of South Vietnam, was almost entirely covered with dense mangrove forests up to 1968. However after extensive spraying of the peninsula in 1967 and 1968, the NAS (1974) concluded that nearly half of the mangrove trees had been destroyed. Mangrove forests were more heavily affected by herbicide spraying than any other vegetation type in South Vietnam. One spray usually killed all mangrove trees (NAS, 1974).

Another limitation of the HERBS tapes, and the maps generated from it, is that the plotted lines represent the center of each mission. The assumed swath width for a sortie was 80 m. Typical missions consisted of