Born in Hamburg, Iowa, in 1918, General Millikan attended Peru State College in Nebraska for two years before he enlisted in the Army Air Corps as an aviation cadet in 1941. He served as a cadet until October 1941 when he accepted a discharge after failing to pass flight checks. He then enlisted in the Royal Air Force where he earned his pilot wings. While in the RAF, he flew combat missions in Hurricane and Spitfire fighters, as a flying sergeant.
Millikan re-entered the US Army Air Corps in October 1942 as a second lieutenant in England. In February 1943 he joined the 4th Fighter Group at Debden, England.
Progressing from second lieutenant to captain, he became commander of the 336th Fighter Squadron of the 4th Fighter Group. During this period, Millikan succeeded in destroying 15 German aircraft (ME-109s and FW-190s) before being forced to bail out over enemy territory as a result of a mid-air collision with his wingman.
Captured by the Germans, he was held prisoner of war until April 1945 when he escaped to friendly forces just prior to the termination of hostilities in May 1945.
On 2 January 1954, then a member of the US Air National Guard he established a new coast to coast record in the US covering 2,530 miles (4,070 km) from Los Angeles to New York in 4 hours 8 min. (time includes stop for fuel at Offutt AFB).
As a command pilot he amassed more than 5,200 hours of fighter time, 1,500 of these in the F-100 Super Sabre. He retired from the USAF with the rank of general.