He enlisted in the 2nd Infantry Regiment of the Missouri National Guard in March 1903 and was discharged in September 1904 with the rank of private.

[2] When the United States entered World War I in April 1917, he was commissioned a first lieutenant in the 128th Machine Gun Battalion, 35th Infantry Division, and served in France until returning home in 1919.

[5] Williams again entered the military when he was appointed major in June 1921 and became commander of the 128th Field Artillery Regiment with the rank of colonel in April 1923.

[8] He was appointed as Chief of the National Guard Bureau in January 1940, with the rank of major general, and served for the entire duration of the US involvement in World War II.

[9][10] During his tenure Williams lobbied to ensure that the National Guard would be considered in the Army's post-war plans, and that it would be included in the newly organized United States Air Force.