Buildings 108 And 113 (Type C Hangars)

Aircraft hangars with annexes housing associated stores, workshops and offices, built in 1937 at RAF Bicester. Designed by the Air Ministry's Directorate of Works and Buildings to drawing numbers 872 and 1581/35, these are Type C hangars - the standard hangar type for the post-1934 Expansion Scheme, of which 155 examples were built across the country.

The buildings have a steel main frame and roof trusses with brickwork in Flemish bond and sheet roofing (which replaced original asbestos slates). Each hangar is a large shed with full-height steel doors at both ends, running to external gantries. A series of single-storey lean-to annexes line either long flank, rising in part to two storeys, which housed workshops, rest rooms and squadron offices.

The roof consists of a series of transverse ridges with hipped ends, set behind a parapet, and features a deep apron above the doors. Along each side wall at mid-height are ten large 32-pane fixed steel casements separated by concrete piers, with continuous sill and lintel bands running beneath them. Above the windows sits a high parapet with flush coping. One bay at each end, also concrete, is slightly brought forward with a higher parapet; a tall single light with horizontal bars is centred to each bay. The short ends contain full-height and full-width steel doors with 12-pane lights at the top, under a deep projecting concrete rail carrying the rolling headgear. Beyond the opening, a light steel lattice beam projects out, supported by a light steel strutted support with steel ground-stops for the doors. Above the doors, contained by the wing walls of the first bays, sits a deep apron with asbestos-cement slate hanging. The doors originally had sand or gravel fill between inner and outer sheeting at the lower panels to enhance blast protection. Annexe windows have been replaced.

Inside, the plain concrete floor is supported by exposed steel stanchions that carry deep lattice trusses in steel channel, double to top and bottom chords, set to the ridges of the transverse roofs and shaped to the hipped ends. At right angles to these are cantilevered members in steel angle at 15-foot (4.6 metre) centres, meeting at and carrying the internal gutters. The bays adjoining the doors have horizontal wind-bracing members. The roof slopes are underlined in softwood square-edged boarding.

The Type C hangar dimensions - 300 feet long, 150-foot span and originally 35 feet clear height (later reduced to 30 feet, as in this example) - were designed to accommodate 100-foot span heavy bombers, enabling the Air Ministry to issue new aircraft specifications to manufacturers. The type evolved from the earlier Type A, with first versions featuring exposed gabled ends; after 1935 the hipped version behind parapets, as here, became standard.

These two hangars were added in 1937 to an earlier pair on the Technical Site at Bicester, separated from the Domestic Site. The four hangars are grouped symmetrically at the end of the axial avenue and share broad concrete aprons. The Technical Site still retains many original buildings, mostly from 1926 with others added during successive phases of the 1930s Expansion Period.

Before perimeter dispersal began in the late 1930s, all aircraft at an operational airfield would be accommodated in its hangars. Their construction consumed a considerable part of building budgets - at Upper Heyford, for example, six hangars accounted for 30 per cent of total construction costs. Military planners closely followed aircraft development through hangar design, a fact that underscores the historical importance of the Bicester group within this uniquely significant site. Although some original detail has been lost, these buildings form a historically important and prominent part of the site as viewed from the flying field.

Bicester is the best-preserved of the bomber bases constructed under Sir Hugh Trenchard's expansion of the RAF from 1923, which was 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 during a period when expansion reflected both domestic political pressures and world events up to 1939. This policy of offensive deterrence dominated British air power and the RAF's independent existence throughout the inter-war period and continued to determine its direction in the Second World War and Cold War afterwards. The grass flying field survives with its 1939 boundaries largely intact, bounded by a group of bomb stores built in 1938-39 and airfield defences constructed 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 Canadian, Australian and New Zealand aircrew as well as British personnel 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 operational units.