Upon graduation from West Point, he was commissioned as a Second Lieutenant. He began primary pilot training at Bartow Air Force Base, Florida, and was awarded his wings in September 1959, when he completed basic  pilot training at Webb Air Force Base, Texas. The General then attended  F-86L interceptor training at Moody Air Force Base, Georgia, and B-52 combat  crew training at Castle Air Force Base, Calif., before reporting to his  first operational assignment as a B-52 co-pilot with the 4038th Strategic Wing, Dow Air Force Base, Maine, in 1960.

A year later he transferred to Homestead Air Force Base, Florida, where he  served as an aircraft commander until June 1965. After completing his graduate studies, General Durkin returned to operational duty by attending C-130 combat crew training at Sewart Air Force Base, Tennessee, and the Replacement Training Unit at Dyess Air Force Base, Texas. In October 1966 he reported to Ching Chuan Kang Air Base, Taiwan, as an aircraft commander.
                                                                       
When he returned to the United States in November 1967, General Durkin was
assigned as a test and deployment officer with Aeronautical Systems Division, Wright-Patterson Air Force Base, Ohio. In August 1968 he transferred to the Armament Development and Test Center, Eglin Air Force Base, Florida, as a program manager for research and development of conventional munitions.
                                                                       
In July 1970 General Durkin entered Armed Forces Staff College and, upon  graduation, was assigned as a staff development engineer, Office of the  Deputy Chief of Staff, Research and Development, Headquarters U.S. Air  Force, Washington, D.C. He remained in Washington, D.C., for four years before moving to Ellsworth Air Force Base, South Dakota, as chief of the Operations and Training Division, 28th Bombardment Wing. He then commanded the 77th Bombardment Squadron there, from April 1976 to July 1977.
                                                                       
After graduation from Air War College, General Durkin served as a nuclear  employment and policy planner and then as chief of the Nuclear Division, organization of the Joint Chiefs of Staff, Washington, D.C., until August 1980. He subsequently became deputy commander for operations, 5th Bombardment Wing, Minot Air Force Base, North Dakota, and, in March 1981, became  wing vice commander. He assumed command of the 28th Bombardment Wing at Ellsworth Air Force Base in October 1981.
                                                                      
In May 1983 the General returned to Air Force headquarters as deputy for  strategic forces, Directorate of Operational Requirements, Office of the Deputy Chief of Staff, Research, Development and Acquisition.
                                                                      
 He remained at Air Force headquarters and served as deputy director of  operations from October 1984 to September 1985, when he became deputy director of plans. In March 1986 General Durkin was assigned as deputy  director for foreign intelligence, Defense Intelligence Agency, Defense  Intelligence Analysis Center. He assumed his last position in October 1987.
                                                                       
General Durkin was a command pilot with more than 4,600 flying hours, including 97 combat missions in Southeast Asia. His military decorations  and awards include the Distinguished Service Medal, Legion of Merit, Defense Meritorious Service Medal, Meritorious Service Medal with oak leaf  cluster, Air Medal with oak leaf cluster, Air Force Commendation Medal with oak leaf cluster, Combat Readiness Medal, Republic of Vietnam Gallantry Cross with Palm, and Republic of Vietnam Campaign Medal.
                                                                     
He was promoted to Major General November 1, 1986, with same date of rank.