 He took courses which included flight in a Taylorcraft and Stearman Biplane, graduating from Iowa State College in 1941 with a bachelor's degree in animal husbandry.He volunteered for service in the US Army in June 1941, serving four and a half years in the Army Air Service.During World War II, Clark trained at Luke Field in Arizona then volunteered to serve in the Glider Pilot Corps, while his brother Joseph was in the Merchant Marine.