Colonel Don A. Hearst was commissioned an Infantry Officer upon graduation from Officer Candidate School on 4 July 1942, Class Number 28. | During company grade, was assigned usual platoon and company commands. As Major, commanded an Infantry Training Battalion for approximately eighteen months. As Lieutenant Colonel, acted as Representative of the Assistant Chief of Staff, DA, to the United States Ambassador to the United Nations and commanded the Special Intelligence Operations for the ACSI at Headquarters First United States Army. Later commanded the ACSI's Special Intelligence Opns at Headquarters USAREUR for approximately three years. As Colonel, commanded the ACSI's Special Intelligence Operations at Army Map Service and, later, commanded the 112th INTC Group at Headquarters Fourth United States Army for approximately three years.