No. 5 Airfield Construction Squadron (5ACS) was a Royal Australian Air Force (RAAF) construction squadron. The unit was first formed in July 1942 and served in the New Guinea Campaign and Borneo Campaign during World War II. The squadron was one of only a few RAAF airfield construction units to be retained at the end of the war, and formed part of Australia's contribution to the occupation of Japan from 1945 until it was disbanded in June 1949. 5ACS was re-raised in August 1951 and worked on several RAAF airfields in Australia. In addition, it also provided small detachments of engineers to support RAAF deployments to South Vietnam and Thailand during the Vietnam War. The squadron was the RAAF's only airfield construction unit from 1961 onward, and was disbanded in December 1974.