On December 22, 1943, Combs enlisted as a private in the U.S. Army for service in World War II.[15] He received his basic training at Fort Knox and participated in the Volunteer Officer Candidate Program, which would have allowed him to attend Officer Candidate School (OCS) immediately after basic training.[13][15] Instead, he was briefly assigned to teach cartography at the Aberdeen Proving Ground in Aberdeen, Maryland before completing OCS in Ann Arbor, Michigan, joining the Judge Advocate General's Corps, and attaining the rank of captain.[9][15] On July 1, 1945, he was sent to the South Pacific.[15] He served as chief of the War Crimes Investigating Department under General Douglas MacArthur in the Philippine Islands, conducting tribunals for Japanese war criminals.[9] Upon his discharge in 1946, he was awarded the Bronze Star and the Military Merit Medal of the Philippines.[6][10]