This primary source comes from the Records of the War Department General and Special Staffs, 1860 - 1952.
Full Citation: Camp Dix, Wrightstown, New Jersey. Learning the use of the gas mask ; 1917 - 1918; Chemical Warfare Service - Drills- Practice; American Unofficial Collection of World War I Photographs, 1917 - 1918; Records of the War Department General and Special Staffs, 1860 - 1952, Record Group 165; National Archives at College Park, College Park, MD. [Online Version, https://docsteach.org/documents/document/camp-dix-wrightstown-new-jersey-learning-the-use-of-the-gas-mask, April 17, 2025]