After graduating from MIT in 1934, Milliken worked in the aircraft industry for twenty years in analysis, wind tunnel and flight testing, with emphasis on stability and control.
He was a founding member of the Watkins Glen Road Races, serving as head of the Rules Committee.
He drove cars such as Type 35 and 54 Bugattis and an ex-Indy Four Wheel Drive (FWD) Miller at Watkins Glen, Pikes Peak, Sebring and many others across North America for 15 years.
As a result of his racing activity, he became interested in automobile stability and control and the potential for applications of aircraft technology.
Prior to his death, his racing career resumed at a private meet at Bridgehampton, New York followed by several appearances at the Goodwood Festival of Speed and at the 50th anniversary of Watkins Glen.