Notwithstanding the fact that toxic-gases had been in almost constant use by the European belligerents for two years before the United States entered the conflict, the declaration of war found us totally unprepared to commence the manufacture of the gas-defense equipment with which every soldier going overseas must be provided. Such an article as a gas-mask had never been produced in this country, the sum total of American knowledge on the subject having been obtained from the masks brought back as souvenirs by war correspondents and displayed in shop-windows and from the pictures in the illustrated papers. Incredible as it may seem, in view of the enormously important rôle which gas was playing on the European battle-fields, only a single American army officer, Major L. P. Williamson of the Medical Corps, had studied the subject of gas defense, and he had done so on his own initiative. Thus it came about that within a few days after the declaration of war, the military authorities, confronted by the imperative necessity of providing our expeditionary forces with gas-defense equipment, were conducting a frantic search among the various scientific departments of the government to discover one possessing the necessary facilities for handling the problem. The Bureau of Chemistry did not have the personnel to carry on the work and the Department of Agriculture did not have the necessary apparatus, but the Bureau of Mines at Pittsburg possessed some experience in kindred problems arising from mine-rescue work, and it also had adequate facilities for handling the experimental work involved. It was, therefore, selected for the purpose. The research facilities at Pittsburg soon proved inadequate, however, and in the summer of 1917 there was taken over the American University Experiment Station, near Washington, where virtually all of the research work connected with the numerous branches of the Chemical Warfare Service was conducted. The Research Division, instead of being dismissed with passing mention, is deserving of a chapter to itself, the services which it performed in the development of gases, protective equipment, and manufacturing processes having been of enormous assistance in the prosecution of the war.