The most common herbicide used was Herbicide Orange , more commonly referred to as Agent Orange : a fifty-fifty mixture of two herbicides 2,4-Dichlorophenoxyacetic acid ( 2,4-dichlorophenoxyacetic acid ) and 2,4,5-Trichlorophenoxyacetic acid ( 2,4,5-trichlorophenoxyacetic acid ) manufactured for the U.S. Department of Defense primarily by Monsanto Corporation and Dow Chemical .