He attained the rank of lieutenant general, and was prominent in the 1950s as military advisor to the Assistant Secretary of Defense for International Security Affairs.

[3] While in college, Fox attended several United States Training Camps that were organized as part of the pre-World War I Preparedness Movement.

[4] In May 1917, his application for a commission was approved, and in June he began attendance at the Fort Riley, Kansas Citizens' Military Training Camp (CMTC).

[5] Assigned to the camp's Fourth Company, Fox completed the officer candidate course in August 1917 and received his commission as a second lieutenant of Infantry in the Organized Reserve Corps.

[5] After receiving his commission following U.S. entry into World War I, Fox was stationed at Camp Funston, Kansas as a member of the 164th Depot Brigade.

[1] After his return to the United States, he served as aide-de-camp to Major General Robert Lee Howze, commander of the Fifth Corps Area at Fort Knox, Kentucky.

[11][12] In the 1920s, the army emphasized polo, with senior commanders believing that the game improved leadership traits in officers by training them to make quick decisions while under stress, and Fox played on several intramural teams.

[1][14][15] In the mid-1930s Fox served as an assistant professor of military science for the Army Reserve Officers' Training Corps program at the University of Maine at Orono.

[19] When the U.S. entered World War II, Fox was promoted to colonel and assigned as assistant chief of staff for operations (G-3) of X Corps during its organization and training in Sherman, Texas.

[21] In 1946, Fox was assigned to Supreme Command Allied Powers (SCAP) in Japan as director of the Office of Economic and Industrial Affairs.