No. 5 Fighter Sector RAAF (5FS) was a Royal Australian Air Force unit formed at Sandfly Gully, Darwin, Northern Territory, on 25 February 1942. It was responsible for fighter aircraft control and coordination in the Darwin region. 5FS plotted and relayed the positions of enemy aircraft to put Allied fighters in an optimum position for interception, in cooperation with RDF and anti-aircraft defences. It was manned twenty-four hours a day. 5FS was renamed No. 105 Fighter Sector on 24 October 1943, and again to No. 105 Fighter Control Unit (105FCU) on 7 March 1944.