William Renick Averill was born in Oak Park, Illinois, on March 8, 1926, son of Renick Herbert and Charline Parks Averill. He attended Hinsdale (Illinois) High School; the Citadel, Charleston, South Carolina; DePauw University, Greencastle, Indiana, and in 1946 received the degree of Bachelor of Arts in Mathematics from the University of Michigan at Ann Arbor. While at DePauw he was a member of the Navy Reserve Officers Training Corps Unit at instruction in the Naval Reserve Officers Training Corps Unit at the University of Michigan. Commissioned Ensign in the US Naval Reserve on June 26, 1946, he subsequently advanced in rank to that of Lieutenant, to date from July 1, 1952.
A member of the Organized Reserve (Intelligence) in the Eleventh Naval District, he had inactive duty between June 1946 and June 1952, except for two weeks periods of Reserve Training in June 1949 and June 1951 at the Operational Intelligence School San Diego, California, and ay the Combat Information Center, Naval Technical Training Center, San Diego, respectively.
Ordered into active military service in June 1952, he reported for instruction at the Naval Intelligence School, Washington, DC. Upon completing the course there in December of that year, he remained for duty on the staff until the summer of 1953 when he was designed Assistant Naval Attaché and Assistant Naval Attaché for Air at Pusan, Korea.