In 1943, as an Army Major in the Field Artillery, Frank Mills volunteered for overseas duty with the Office of Strategic Services (OSS). After training in Special Operations, he was ordered to London to join the combined Special Forces Command of British, French and Americans, to support Resistance efforts in Europe as part of the Allied invasion of France. With OSS Special Forces Detachment 10, he landed in the D-Day Invasion with advance elements of the First Infantry Division on Omaha Beach. He coordinated Resistance activities with the operations of First Army as they moved through France.When the German forces had been driven out of France in late 1944, he was named OSS Chief of Special Operations for the Central Field Command in China. In that capacity he was in charge of all OSS guerrilla warfare against the occupying Japanese Army in the area extending about 1,000 miles north from the Yangtze River - an area about the size of the United States. He remained at that command until September, 1945.After the war he served with Army Intelligence in the Pentagon and with British Military Intelligence in London, where he worked for two years under Major General Gerald Templar of Burma fame. Later he served with the 11th and 82nd Airborne Divisions, and for many years he helped develop the Army's Special Forces (The Green Berets). He served with Admiral Radford, Commander in Chief, Pacific, where he developed Unconventional Warfare plans for the Asian area. He was a Plans Officer at Headquarters, Eighth Army in Korea.From 1959 to 1961 he was Commanding Officer of the First Special Forces Group on Okinawa for operations throughout Asia, including Viet Nam. His next assignment was Assistant Commandant of the Special Warfare School at Fort Bragg during a period of rapid expansion, where he was awarded his second Legion of Merit. In 1964 he was named Chief of Special Plans for South America, Africa and the Middle East at U.S. Strike Command, MacDill AFB. He was teaching Counter-insurgency and Guerrilla Warfare at the Armed Forces Staff College when he retired from the Army in 1967 after 27 years of active duty.