The Squadron began on 4 February 1941 as No. 401 Flight of RAF Bomber Command. When all the meteorological flights were put under RAF Coastal Command it became No. 1401 Flight. On 1 August 1942 at RAF Bircham Newton the flight combined with 1403 flight to form No. 521 Squadron. It took part in Coastal Command's Meteorological operations The squadron had inherited from its 1401 flight aircraft such as Gloster Gladiator biplanes and some Hawker Hurricanes. From 1403 flight came its Bristol Blenheims and Lockheed Hudsons. Later the squadron received some Supermarine Spitfires and de Havilland Mosquitos. The operations of the original Flights and later the Squadron was taking meteorological information for weather forecasting – previously provided by merchant shipping to the Met Office. The aircraft would take measurements of temperature and humidity in set areas over the North Sea from an altitude of 40,000 ft downwards. The squadrons Mosquitos would operate on "PAMPA" flights that took them deep into occupied Europe to assess the weather over target areas for the bombers. On 31 March 1943 at Bircham Newton the squadron was split into nos. 1401 and 1409 Flights.
Second formation
The squadron reformed on 1 September 1943 at RAF Docking, a satellite of the Bircham Newton station, adding to its original equipment Handley Page Hampdens, but doing without the earlier Mosquitos and Blenheims. In December 1943 the squadron received Lockheed Venturas to replace its Hudsons. Additional Hurricanes arrived in August 1944, to supplement the aging Gladiators, which were still on strength. Hudsons arrived again in September 1944, because the Venturas were needed elsewhere. In October 1944 the squadron moved a few miles to the other satellite of Bircham Newton, RAF Langham. For long-range missions the squadron received some Boeing Fortresses in December 1944, which were supplemented after the end of the war with Handley Page Halifaxes, by which time the squadron operated from RAF Chivenor, where the unit disbanded on 1 April 1946.
