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.  
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