Buildings Nos 79 And 137 (Type 'A' Hangars)

RAF Bicester: Buildings Nos 79 and 137 (Type 'A' Hangars)

These are aircraft hangars with attached stores, workshops and offices built in 1926 by the Air Ministry's Directorate of Works and Buildings to drawing number 19a/24. The construction uses steel main frames and roof trusses, concrete in-situ wall panels, some brickwork in Flemish bond, and corrugated asbestos or asbestos slate roofing.

Layout and Exterior

Each hangar is a large shed with full-height steel doors at both ends, running on external gantries. A series of single-storey lean-to annexes line each long side, rising in part to two storeys.

At each end are two pairs of sliding doors with bolted sheet steel cladding on steel framework, though the upper half has corrugated steel. Braced steel gantries on each side support the doors when open. Each long elevation has seven gables constructed in brickwork, with encased steel external stanchions extending almost to each ridge and flush secondary stanchions at the valleys. Below these runs a continuous strip of patent glazing in nine lights per bay, except the two end half-bays. Above the glazing, cantilevered steel brackets support a steel-framed catwalk running the full length of each side, with steel ladder drops at the ends enclosed in open cylindrical protective shafts. The concrete infill below the glazing is cast in horizontal lifts of approximately 450 millimetres.

The annexes feature varied steel sashes set flush with concrete lintels and stooled sills. One section of each hangar contains an eight-bay two-storey office unit. Large square hopper-heads collect rainwater from the main roof and feed downpipes.

Interior

The interior displays the standard framework for a Type 'A' hangar: deep open trussed beams with double bottom chord, all in I-section steel, bear the ridges and carry a series of transverse trusses in steel flat and angle sections. These are cantilevered out to a steel valley beam, which is in turn carried by vertical stanchions set flush to the concrete walling. Horizontal wind-bracing is positioned at each end immediately adjacent to the doors.

Historical Context

The dimensions of the Type 'A' hangar—249 feet (75.9 metres) long and 122 feet 5 inches (37.3 metres) span—were determined in November 1923 discussions between the Aerodrome Board and the Directorate of Works and Buildings. The design was based on accommodating the RAF's largest projected twin-engined bomber, the De Havilland DH9A, with each hangar envisaged to house twelve machines. The Type 'A' aircraft shed became the standard hangar for Trenchard's Home Defence Expansion Scheme, designed in 1924. Thirty-four examples were built on seventeen sites, serving as the RAF's standard hangar from 1924 until the 1930s.

Six Type 'A' hangars were originally planned for Bicester, but financial restrictions on Trenchard's scheme limited construction to just two. In 1936, two Type 'C' hangars were added. The four hangars are grouped symmetrically at the end of the axial avenue, sharing broad concrete aprons. Until the late 1930s onset of perimeter dispersal, all aircraft of an operational airfield—typically an omni-directional flying field of 1,000 yards diameter—would be accommodated in its hangars. Hangar construction consumed a considerable portion of construction costs for new sites; the six hangars at Upper Heyford, for example, took up 30 per cent of its total budget. Military planners therefore shadowed aircraft development through the planning and development of hangar buildings, a fact which underscores the importance of the Bicester group and their relationship to this uniquely important site.

RAF Bicester

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, based on the philosophy of offensive deterrence. It retains, better than any other military airbase in Britain, the layout and fabric relating to both pre-1930s military aviation and the development of Britain's strategic bomber force in the period up to 1939, reflecting how its expansion mirrored domestic political pressures as well as events on the world stage. This policy of offensive deterrence essentially dominated British air power and the RAF's existence as an independent arm of the military in the inter-war period, and continued to determine its shape and direction in the Second World War and afterwards during the Cold War.

The grass flying field still survives with its 1939 boundaries largely intact, bounded by a group of bomb stores built in 1938–39 and airfield defences built in the early stages of the Second World War. For much of the Second World War, RAF Bicester functioned as an Operational Training Unit, training Canadians, Australians and New Zealanders as well as British air crews for service in Bomber Command. These OTUs, of which Bicester now forms the premier surviving example, fulfilled the critical requirement of enabling bomber crews—once individual members had trained in flying, bombing, gunnery and navigation—to form and train as units.

Military flying at Bicester commenced in 1918 when the new aerodrome was established as a three-squadron Training Depot Station. The site was demolished after closure of the base in 1920, but it was selected as a bomber station by the Aerodrome Board as part of Trenchard's Home Defence Expansion Scheme, sanctioned by Baldwin's government in June 1923. General Sir Hugh Trenchard founded the independent status of the RAF upon the concept of offensive deterrence, a principle he shared with Italy's Marshall Douhet and America's General Mitchell. This doctrine envisaged fleets of self-defending bomber formations as the instrument of war most likely to ensure swift victory in any future conflict, and underpinned the justification for the Strategic Bomber Offensive in the Second World War.

The RAF's infrastructure was subject to severe political fluctuations in the inter-war period, resulting from both events on the world stage and political and financial pressures at home. Only two of the proposed six Type 'A' hangars at Bicester for the three-squadron station, for which plans were drawn up in August 1926, were built, due to an early deceleration in Trenchard's programme. The next major phase of building formed part of the post-1934 Expansion Period, prompted by the collapse of the Geneva disarmament talks in 1933.

The station opened in January 1928, with the 10th of that month seeing the arrival of Hawker Horsleys from Spittlegate. The fabric and layout, planned on dispersed principles, retain an identifiable 1920s character and provide examples of the first permanent buildings erected for RAF operational stations. Air Commodore (later Air Chief Marshall Sir) Edgar Ludlow-Hewitt, President of the Aerodrome Board until late 1925 and Commander-in-Chief of Bomber Command early in the Second World War, was responsible for the selection and outline planning of these stations, often in close collaboration with Trenchard. Designs for the built fabric were developed in detail by the staff of the Director of Works and Buildings (Major-General Sir Andrew M Stuart, and Major-General Sir William A Liddell from April 1924 to July 1929).

The most prominent technical buildings, most notably the guardroom (Building 89) and station headquarters (Building 47), and the buildings on the domestic site were designed in a simple, astylar, neo-Georgian style. The domestic buildings were laid out in an open plan manner, more formally than the technical site to the east, thus enabling the principal buildings around the parade ground area to play a particularly important role in defining the character of the site.

The planning of the technical site is dominated by a strong east-west axis from the west entrance to the flying field. This road is tree-lined and flanked by the 1920s motor transport group (Buildings 129, 130 and 131), armoury (123) and workshops (90 and 99). It provides clear views towards the hangars to the east and, across the A421, the domestic site to the west. From the west entrance, flanked by the impressive group of Station Headquarters and Guardhouse (Buildings 146–147 and 89), two service roads branch out: one to the north-east serving the power house and water supply group (Buildings 81, 82 and 84), and one to the south-east serving the Air Ministry Works Department Group (Building 144) and the now-demolished coal yard. The latter, and the main workshops (Building 99), were served by an Air Ministry railway which entered the site from the east.

The 1930s extensions and new buildings carefully match the style of the 1920s scheme. Whilst the married quarters to the north of Skimmingdish Lane and the west of Buckingham Road drew their inspiration from the Garden City Movement, the neo-Georgian officers' mess (Cherwood House, Buckingham Road) and married quarters off Skimmingdish Lane reflect the distinct change in the aesthetic quality and design of RAF stations which resulted from the Air Ministry's consultation with the Royal Fine Arts Commission and appointment of an architectural advisor to the Directorate of Works and Buildings in 1934.

The buildings constructed in 1939 for Scheme M, notably the decontamination centres, boiler and power houses and flat-roofed barracks buildings, are characterised by developed Art Deco characteristics. Buildings 23, 25 and 20 are distinguished by flat protected concrete roofs—to counter the effects of incendiary bombs and minimise the effects of bomb blast—and the use of glazing detail and string courses to give a much more streamlined horizontal design. The increase in aircraft at Bicester was marked by the completion of new Type 'C' hangars in 1937, and the building of a new control tower in 1938 reflected the increased importance given to the need to control movement with the defined zoning of serviceable landing and take-off areas.

1938 saw the arrival of Blenheim bombers, which replaced the obsolete Overstrands with which many airfields had been equipped into the mid-1930s. In October 1939 the first Halifax prototype made its maiden flight from Bicester. From 1938 to October 1944 Bicester served as an Operational Training Unit, mainly for the training of pilots, observers and gunners for the Blenheim crews of 2 Group. The outset of the conflict saw the completion of the bomb stores group to the south and construction of pillboxes and trenches for the close defence of the airfield, now surviving on the east side of the hangars and in a group to the south of the flying field. The flying field was considerably enlarged to the north and south, with tracks and 'panhandle' standings for the dispersed parking of aircraft characteristic of Second World War bomber stations.

RAF Bicester functioned as an Operational Training Unit until October 1944, training Canadians, Australians and New Zealanders as well as British air crews for service in Bomber Command. Crews for the medium bomber units in the Middle East and then the Far East were formed and trained at Bicester and Upwood, with Mosquitos replacing the Blenheims from January 1944. From autumn 1943 it was already serving as a Forward Equipment Unit for the logistical support of Operation Overlord.

After 1945, 71 Maintenance Unit formed here as one of the principal aircraft salvage units responsible for southern England. Crashed aircraft were brought here and reconstructed in one of the hangars for crash investigation purposes. This use, together with its role as a gliding school and the administrative use of the domestic site (DCTA Caversfield), has ensured the preservation of the inter-war character of the site and the rare and consistent preservation of exterior detail and fitments. Post-war redevelopment and encroachment by quarrying has removed most of the Second World War extensions to the flying field.