 Fries arrived in Europe as World War I raged, he expected to do more engineering work but was instead thrust into heading the fledgling Gas Service Section, AEF.The Gas Service Section was mostly constituted by the 1st Gas Regiment (originally the 30th Engineer Regiment (Gas and Flame)) and Fries commanded the section.He became the chief of the Overseas Division of the Chemical Warfare Service in 1919, and when William L. Sibert retired in 1919, Fries became the first peacetime overall chief of the Chemical Warfare Service the following year.