a, b and c represent known volumes of Agents Orange, White and Blue, respectively, sprayed by US military forces in RVN, 1961−1971. Volumes are calculated for individual grids spaced at 0.01 degrees ( 1.2 km2), that divide up Vietnam in a geographic information system developed by us45. Colours in a, b and c correspond to volumes as shown in key. Arrows in a and c point to missions in Laos and in the Parrot's Beak region of Cambodia, respectively. d, Grids sprayed with volumes greater than 4,800 l (about 10% of total), with marker size increasing in proportion to volume and colours corresponding to herbicide codenames. All herbicides containing 2,4,5-T are represented by orange markers.
The data are taken from the corrected HERBS file and do not include Dinoxol and Trinoxol used in 1961.
At least 19,905 sorties were run between 1961−1971 (1−34 daily, with a daily average of 10.7 sorties). These data disagree with USAF estimates18. The number of daily sorties mirrors the course of the Vietnam War itself: a slow build-up, maximum activity 1968−1969, then a slow but steady decline. The abrupt spraying drop-off at the end of January 1968 corresponds to the Tet Offensive wherein North Vietnamese forces carried out massive, coordinated attacks throughout RVN for nearly 2.5 months. Spray equipment was removed from Ranch Hand aircraft and crew and aircraft participated in airlift operations.