Building No 99 (Main Workshops)

Workshop for airframe and engine repairs, welders' bay and fabric-workers shop, built in 1926. Designed by the Air Ministry's Directorate of Works and Buildings to drawing number 1788/25.

The building comprises a group of three linked gable single-storey sheds arranged around a narrow central courtyard, with infilling flat-roofed elements and enclosed at the outer end. The structure is built of stretcher bond brickwork with a brick stack and asbestos-cement slate roof. All parts are generously fenestrated with large steel casements set to flush concrete lintels and stooled sills. All three sheds have patent roof glazing to both slopes. The gable ends each have wide doorways, with one being a later roller version, and a pair of plank doors serving the narrow courtyard entrance. The interior contains a series of steel trusses supported on brick piers, creating various well-lit working areas.

The building forms part of the Technical Site at Bicester, separated from the Domestic Site, and has been little altered since construction. It is strategically positioned between two 'A' type hangars and faces the main avenue bisecting the site, leading to the flying field. Built during the initial permanent designs for Britain's independent air force, the workshops served an integral function in the Technical Site's operations.

Bicester is the best-preserved of the bomber bases constructed as the principal arm of Sir Hugh Trenchard's expansion of the RAF from 1923, which was based on a philosophy of offensive deterrence. The site retains the layout and fabric relating to pre-1930s military aviation and the development of Britain's strategic bomber force better than any other military airbase in Britain. The grass flying field still survives with its 1939 boundaries largely intact, bounded by bomb stores built in 1938–9 and airfield defences built in the early stages of the Second World War. During much of the Second World War, RAF Bicester functioned as an Operational Training Unit, training Canadian, Australian and New Zealand air crews as well as British personnel for service in Bomber Command. These OTUs fulfilled the critical requirement of enabling bomber crews to form and train as units once individual members had trained in flying, bombing, gunnery and navigation.