This article analyzes a World War II-era Army field jacket and the principle of layering it represents as a technology of war. The M-1943 jacket, designed in military laboratories and issued to soldiers in the European Theater, represents a scientized approach to layering clothing developed on test expeditions and in new research and development laboratories run by the Quartermaster Corps. Drawing on both histories of technology and histories of design, this article shows how the M-43 jacket operated as part of a broader assemblage of testing facilities, institutions, and individuals. The debate within the Army about how best to equip soldiers points to the struggle to control the growing authority of scientific expertise in the military bureaucracy. The science of dress, more than personal or subjective experience, shaped how the American military equipped soldiers for war and contributed to the expansion of military research laboratories in the Cold War.