This is the third and final volume of the Chemical Warfare Service subseries of The Technical Services in the series UNITED STATES ARMY IN WORLD WAR II. Concluding the chemical warfare story that was begun in Organizing for War and was continued in From Laboratory to Field, Chemicals in Combat records in meaningful detail the ultimate and most rigorous test of all things military: performance in battle. Entry of the United States into World War II found the nation's Armed Forces, like those of its principal allies and enemies, mindful of the possibility of gas warfare. The gas attacks of World War I did not recur, but the Chemical Warfare Service was in the position of being ready for a type of war that did not happen. Thus the CWS, the only technical service having combat troops armed with weapons it had specifically provided for itself, was forced to show its flexibility. The Service sought to fulfill its supporting role with smoke, flame, and incendiaries; with 4.2-inch mortars and flame throwers; and, having no gas to contend with, its decontamination companies provided front-line troops with the means for simple physical cleanliness. Chemicals in Combat recounts the administrative, logistical, and tactical problems arising from the Service's dual responsibility, and highlights the flexibility and ingenuity demanded of chemical troops in World War II. These are, of course, qualities that military men have and will always find essential.