No. 4 Squadron is a Royal Australian Air Force squadron composed of the air force special forces Combat Controllers, aircrew who operate the Pilatus PC-21 aircraft and instructors for the Australian Defence Force Joint Terminal Attack Controller (JTAC) course.
The squadron was previously a fighter and army co-operation unit active in both World War I and World War II. Formed in late 1917, the squadron operated on the Western Front as part of the Australian Flying Corps until the armistice in November 1918. It was disbanded after the war in mid-1919, but re-raised in 1937 and 1940. In 1942 it deployed to New Guinea, where it supported military forces by spotting for artillery and providing reconnaissance and close air support. As the war progressed, the squadron took part in the Huon Peninsula, New Britain and Borneo campaigns. It was disbanded in early 1948, but was re-formed on 2 July 2009 to provide training to forward air controllers and to support Army Special Operations Command.