No.542 Squadron was formed on 19 October 1942 at Benson from A and E Flights of the Photographic Reconnaissance Unit. Using nearby Mount Farm as its operational base for a time, the squadron used Spitfires for photographic reconnaissance missions over Europe until disbanding on 27 August 1945. On 17 May 1954, No.542 reformed at Wyton with photographic reconnaissance Canberras, but disbanded again on 1 October 1955. On 1 November 1955, it reformed from No.1323 Flight at Wyton, moving in the following month to Weston Zoyland to prepare for its detachment to Australia to carry out survey and sampling flights during the nuclear bomb tests in 1956-57. In April 1957 it returned to the UK and was renumbered No.21 Squadron on 1 October 1958.
