Fenn was active in the "Yale system" of Chinese grammar developed by himself, George Kennedy, Gardner Tewksbury,
Wang Fangyu and others working in the Institute of Far Eastern Languages (IFEL) at
Yale in the late 1940s. During
World War II, he conducted a Chinese program at Yale for the military. He was director of the IFEL from 1952 to 1962. He then became director emeritus. After his mandatory retirement from Yale, he set up a Chinese language department at
Dartmouth College. Starting in 1966, he spent three years at
Washington University in St. Louis. At Washington University, he was the acting chairman of the department of Chinese and Japanese from 1966 to 1967. He retired in 1968. ==Selected works==