Williams came from a working-class background in South Australia. He was a lieutenant in the Army when he learned to fly at Point Cook, Victoria, in 1914. As a pilot with the Australian Flying Corps (AFC) in World War I, Williams rose to command No. 1 Squadron AFC, and later 40th Wing RAF. He was awarded the Distinguished Service Order and finished the war a lieutenant colonel. Afterwards he campaigned for an Australian Air Force run separately to the Army and Navy, which came into being on 31 March 1921.
