RAF Syerston was built as part of the bomber expansion in the late 1930s, but did not open until 1 December 1940. The first aircraft were Vickers Wellingtons crewed by Polish flyers who had joined the RAF. In July 1941, they were replaced by members of the Royal Canadian Air Force (RCAF), flying Handley-Page Hampdens. From December 1941 until 5 May 1942, the base was closed whilst a concrete runway was built with two T2 hangars. When it re-opened, it became part of No. 5 Group. In 1942, several squadrons of Avro Lancaster aircraft arrived.