William Eastman was born on September 23, 1928, in Providence, Rhode Island. He enlisted in the Rhode Island Army National Guard on October 14, 1947, and served in the field artillery until he enlisted in the U.S. Air Force on March 31, 1948. Sgt Eastman served as a Woodworker in the Air Force until leaving active duty and going back into the Rhode Island National Guard on September 4, 1953. He went on active duty in the U.S. Army on January 8, 1954, and was trained in the Quartermaster Corps. His next assignment was as a Clothing and Textile Repairman with the 534th Quartermaster Company from January 1954 to August 1957, followed by Airborne Training at Fort Benning, Georgia, from August to September 1957. Sgt Eastman served as a Section Chief with the 109th Quartermaster Company at Fort Lee, Virginia, from September 1957 to December 1961, and then as a Section Chief at the Quartermaster Training Center at Fort Lee from December 1961 to July 1965. His next assignment was as an Airborne Operations Sergeant with the Air Drop Division at Evreux, France, and then at Nahbollenbach Army Depot, West Germany, from July 1965 to June 1968, followed by service as an Instructor at the U.S. Army Quartermaster School at Fort Lee from July 1968 to July 1969. Sgt Eastman then deployed to Southeast Asia where he served as a Platoon Sergeant with the 109th Quartermaster Company in South Vietnam from August 1969 to August 1970, and then as an Instructor, Senior Instructor, Chief Instructor, and Supervisor back at the Army Quartermaster School at Fort Lee from September 1970 until his retirement from the Army on April 30, 1975. While in the Army, MSG Eastman completed his bachelor's degree in psychology and later his master's degree in education and psychology. He taught history and psychology in Petersburg, Virginia until his death on November 25, 1991, and he was buried at the Sunset Memorial Park Cemetery in Chester, Virginia. William was married to Shirley Frances Auen Eastman from October 10, 1959, until his death, and they had four children together; Tamara Jane Eastman, born in 1961; William Darren Eastman, born in 1963; Eric Charles Eastman, born in 1965 (died in 2001); and Michael Patrick Eastman, born in 1972.

His Bronze Star Medal Citation reads:

For distinguishing himself by exceptionally meritorious service in connection with ground operations against a hostile force in the Republic of Vietnam during the period August 1969 to August 1970. As a result of his keen professionalism and remarkable dedication to mission fulfillment he was able to achieve maximum results in every endeavor. Each facet of his service was characterized by outstanding accomplishment and a superior manner of execution. Through his sound technical knowledge and pragmatic approach he significantly enhanced the successful accomplishment of the mission of this command. His performance was in the best tradition of the military service and reflects great credit upon himself, his unit, and the United States Army.