What was the name of the controversial herbicide used by the United States during the Vietnam War to defoliate jungles?

During the Vietnam War, the U.S. military's Operation Ranch Hand sprayed millions of gallons of a powerful chemical defoliant over the dense jungles of Southeast Asia. The goal was to remove the thick canopy that provided cover for enemy forces and to destroy their food crops. This specific chemical mixture became infamously known by the color-coded stripe on its 55-gallon storage barrels. It was the most widely used of several "Rainbow Herbicides" deployed during the conflict.

The devastating and long-lasting controversy stems not from the herbicide itself, but from a toxic contaminant created during its manufacturing. The mixture contained two herbicides, but one of them was tainted with a highly poisonous byproduct: a dioxin known as TCDD. This potent and persistent chemical has since been linked to a horrifying range of health issues, including various cancers, severe birth defects, and neurological disorders. The legacy of this contamination continues to affect the health of countless American veterans and generations of Vietnamese civilians to this day.