In April of 1915, the German-Jewish chemist Fritz Haber supervised the first deployment of industrialized chemical weapons against French colonial troops. The uncertain nature of the attack, both in its execution and outcome, led many German military men to question the controllability of poison gas. Over the next three decades, Germans would continue this line of inquiry, as aero-chemical attacks appeared increasingly imminent. This article narrates the German search for control over chemical weapons between the world wars, revealing the ways in which interwar techno-nationalists tied the mastery of poison gas to ethno-racial definitions of Germanness. Under the Nazis, leaders in civilian aero-chemical defense picked up this interwar thread and promoted a dangerous embrace of gas that would supposedly cull the technically superior Germans from other lesser races. Although this vision of a chemically saturated world did not suffuse German society, such logic did play out in the gas chambers of the Holocaust.