 Returning to Denver, he worked a systems engineer for United Airlines while performing for the Denver Philharmonic Orchestra (then known as the Denver Businessmen's Orchestra) and studying under its conductor, Antonia Brico.He was drafted by the US Army in 1961 and contributed to developing large systems for the Pentagon's National Military Command and Control Center, where he was named Chief Programmer for global nuclear war-game exercises.After receiving an honorable discharge from the army, Cornwall returned to the airline industry, where he developed some of the first online systems for flight planning and real-time monitoring.