After growing up in California in the 1920s and 1930s, Engen entered the Navy through the V-5 aviation cadet program and was designated a naval aviator in June 1942. In 1943-44 he flew an SB2C Helldiver in Bombing 19 (VB-19) and took part in the Battle of Leyte Gulf. In 1944-45 he flew in Bombing-Fighting 19 (VBF-19). Shortly after World War II he worked briefly as a civilian test pilot for Consolidated Vultee and was a student at the University of California at Los Angeles. In the next few years, as a fighter pilot, he was in Fighting 212 (VF-212), Fighter Squadron 52 (VF-52), and Fighter Squadron 51 (VF-51). In the summer of 1950, during the Korean War, he was part of the U.S. Navy’s first-ever jet sortie in combat. Other tours in the 1950s included General Line School at Monterey, California; Bureau of Aeronautics representative in Dallas; the Empire Test Pilots’ School in Britain; and Air Development Squadron Three (VX-3). He served 1955-57 as executive officer of Fighter Squadron 21 (VF-21) and in 1957-59 at the Naval Air Test Center, Patuxent River. In 1959-61 he was PCO and skipper of Fighter Squadron 21 (VF-21). Early 1960s duties included command of Carrier Air Group 11 and as operations officer in the aircraft carrier Coral Sea (CVA-43). In 1964-65 Engen commanded the ammunition ship Mount Katmai (AE-16), was a student at the Naval War College in 1965-66, and in 1966-67 commanded the aircraft carrier America (CVA-66). In the late 1960s he completed his bachelor’s degree at George Washington University, headed the Aviation Plans Branch of OpNav, and was selected for flag rank. He served 1969-71 in the Strategic Plans Division of OpNav, then commanded Carrier Division Four, 1971-73. From 1973 to 1976 he was Deputy Commander in Chief U.S. Naval Forces Europe (CinCUSNavEur) in London. During the latter part of 1976 he was Assistant DCNO (Plans and Policy) and from 1976 to 1978 was Deputy Commander in Chief Atlantic Fleet.
After Engen retired from active naval service in 1978, he was general manager of Piper Aircraft, Lakeland, Florida, and later worked with Ketron, Inc. On re-entering government service in 1982 he was on the National Transportation Safety Board, and later served 1984-87 as Federal Aviation Administration Administrator. His post-retirement activities included flying and work at the Smithsonian’s Air and Space Museum.