In addition to his career in education, Williams also had a successful military career. He first served as a First Lieutenant with the Indiana National Guard near the Mexican border in 1916 during the Mexican Border Expedition. On April 17, 1917, Indiana University established a military training program in Bloomington called the Student Army Training Corps with Williams in command. In 1919, the Student Army Training Corps was renamed the Reserve Officers Training Corps. From the years 1917 to 1919, he served in the Rainbow Division as a U.S. Army Captain of Field Artillery with the American Expeditionary Force. From 1921 to 1931, he served as an officer in the Indiana National Guard Field Artillery. From 1931 to 1939, he served as a Colonel and the Chief of Staff of the 38th division of the Indiana National Guard before commanding the 113th Quartermaster Regiment, and eventually becoming Quartermaster of the 38th division in national service.