This article investigates the use of coca by the Bolivian Army during the Chaco War of 1932–35. I present research that reveals the surprising extent to which the Bolivian Army provisioned coca to its soldiers as a substitute for adequate nutrition; as a morale booster; as a stimulant; and as a medicine. The article explores the social and cultural implications of mass coca consumption by Bolivian soldiers, many of whom were mestizos who had never before chewed the leaf. Ultimately, I argue that the pervasiveness of coca within the traumatic popular experience of the Chaco War sowed the seeds of a historic transformation of the politics of coca in Bolivia. The Chaco War initiated a process by which coca in Bolivia was transformed from a neo-colonial marker of the Indian caste to a material and symbolic element of an emergent interethnic working class. Through a comparative analysis of the Bolivian army's use of coca in the Chaco War with the German army's use of methamphetamine during World War II, this article concludes with a consideration of the ways in which the present case study expands our understanding of the crucial but under-studied historical relationship between drugs and warfare.