Returning to the United States as the commanding officer at Watertown Arsenal, he again traveled to Europe at the end of 1914 as American military observer with the German Army for six months. Now, a lieutenant colonel, he again took up duties with the Joint Gun Forgings Board from May 1915 until June 1916. Following eight months as the ordnance officer for the Southern Department of the Army during the mobilization of Regular Army and National Guard units for the Punitive Expedition, he was called to Washington at the end of February 1917, to become assistant chief of ordnance. With American entry into World War I in April 1917, he traveled to France as the chief ordnance officer for the American Expeditionary Forces. Williams spent eleven months there, during which time he was advanced two grades to the rank of brigadier general.