It was used primarily in what the Pentagon called Operation Ranch Hand, which lasted from 1962 until 1970.  
It was used primarily in what the Pentagon called Operation Ranch Hand, which lasted from 1962 until 1970.  Known by the shorthand notation 2,4,5-T, it was always contaminated with an unavoidable by-product of its production process, 2,3,7,8-TCDD, an especially dangerous form of dioxin.  Named for the colorful stripe on the 55-gallon drums in which it was shipped, for 10 points, what was this defoliant extensively sprayed by U.S. Air Force C-123s over central and southern Vietnam?
It was used primarily in what the Pentagon called Operation Ranch Hand, which lasted from 1962 until 1970.  
Agent Orange