Type D Hangars, Site D

TYPE D HANGARS, SITE D, KEMBLE BUSINESS PARK

Two aircraft storage hangars built in 1939 to Air Ministry Directorate of Works and Buildings drawings Nos 3212-1313/36. Constructed in reinforced concrete walls and roof with asphalt covering, though one hangar is now partly roofed in profiled metal sheet.

The hangars are identical except for small side annexes. They are set at an obtuse angle to each other, approximately 200 metres north of the east end of the main runway. Each hangar has a rectangular plan with internal dimensions of 300 by 150 by 30 feet clear (91.4 by 45.7 by 9.1 metres). Full width and height doors at each end slide to external gantries. The basic form is a plain cuboid with a segmental roof.

The long side walls are plain in-situ cast concrete. A continuous window range runs at high level, comprising horizontal steel lights in six panes divided by slightly projecting concrete columns, with a continuous sill to a plat-band. Above these windows a deep flat canopy projects approximately one metre. Above the canopy a plain high parapet continues in the wall plane, approximately 1.5 metres high. This parapet returns to the short ends for a short run before merging with the segmental pediment above a horizontal projecting rail carrying the head track to the doors. This track continues beyond the ends of the hangar as a gantry supported at the outer ends by plain concrete posts. At each end are six full-height steel doors, each containing a horizontal four-pane glazed light centred at the top.

The easternmost hangar has a small lean-to annex on the south side covering five bays but with nine steel casements and a door at each end. The walls are rendered on block or brick and the roof is corrugated asbestos sheet. The north side is plain. The second hangar has a series of later additions with flat roofs on the east side, with three large steel vents with conical cappings, and also an earlier lean-to with corrugated asbestos sheet roof. On the west side is a lean-to range similar to that on the first hangar. Part of the roof at the south end has been recovered with later sheeting, and there are three large roof vents identical with those on the east side.

Internally, each hangar is divided into fifteen bays with a plain concrete floor. Concrete piers at 20 feet (6.1 metres) centres are expressed internally, with plain cast concrete walling up to sill height. Each pair of piers carries one of the bow-string roof trusses, formed in square concrete sections with straight bottom chord and segmental upper chord. These are separated by a series of square vertical suspenders with a longitudinal bar stiffener to the central sections. At the pier supports are short lengths of solid bracing, and at about two metres from the wall is a purlin ring running the full length on each side. Horizontal wind-bracing is set to the bay immediately adjacent to the doors at each end. The roof decking is in-situ concrete following the segmental profile.

The Type D hangar, which combines concrete construction with bow-string trusses, owes its origin to developments in French engineering, such as at the historic Montaudron airfield at Toulouse. A total of 34 examples of these all-concrete designs were used on Aircraft Storage Units such as Kemble, which has two further examples on Main Site. These are included in the listing because of their engineering virtuosity and their integral relationship to this uniquely important site.

Kemble, by virtue of its range of five different hangar types including structurally advanced ones of parabolic form, is the most outstanding and strongly representative of the 24 Aircraft Storage Units planned and built by the Air Ministry for the storage of vital reserve aircraft in the period 1936-1940. The Aircraft Storage Units were all administered by Maintenance Command and were sited to the west of the principal bomber stations and fighter belt. Their function was to receive and store aircraft before they were made ready to be sent to operational bases. Some, such as Hullavington to the south, were grafted onto existing Flying Training Schools. Apart from a cluster of three hangars on the Main Site, the hangars were planned in pairs around the flying field. The planners of Aircraft Storage Units thus exercised, for the first time, the principle of 'dispersal' in the planning of military airfield landscapes as opposed to fabric, the planning of domestic and technical sites having integrated these requirements from the 1920s. The dispersal of aircraft around the flying field, instead of being concentrated in the hangars, provided further protection against air attack (particularly crucial for the vital supplies of reserve aircraft to front line units) and had a profound influence on airfield layout during the Second World War. This principle also had an effect on hangar design in Aircraft Storage Units, in the use of both concrete and roofs of parabolic form—the latter originally turfed over for additional protection—which housed aircraft in the 'tails-up' position hung from their roofs.

The genesis of the parabolic Lamella type of hangar is the Lamellendach technique, produced by Junkers in Germany from the early 1920s, which utilised a structural grid of short and small-scale steel sections in a diagonal grid in order to create a parabolic vault. This type of hangar was built in England under licence from 1929, and there are four at Kemble (Sites A and B). In addition there are two variants in construction, using the same overall form and dimensions but developed differently: Type L uses close-spaced concrete ribs formed in pressed steel members (Sites F (not included) and C) and Type E uses ribs of small-section steel to support concrete slabs curved to the arc of the frame (Site E). These steel and concrete rib hangars most clearly relate to contemporary experimentation elsewhere in Europe, especially Pierre Luigi Nervi's Lamella-derived forms built for the Italian air force, the Zeiss-Dwidag concrete-ribbed vaults used for side-opening hangars in Germany and the concrete hangars developed for the French air force from the 1920s. All these hangar buildings stretched existing engineering technology in order to clear wide spans, forming the basis for developments in the post-war period. The existence of such a variety of these types of hangars at Kemble, also relating to an advanced type airfield landscape, is certainly unique in a British context, and no such group survives in France or Germany.

RAF Kemble was officially opened in June 1938, but construction continued into 1939 and a Station Headquarters was not formed until October 1940, under 41 Maintenance Group. By November over 900 personnel were involved, many of them civilians, staffing the Maintenance Unit. Most were accommodated off-site, and others were in hutted units, mostly in Kemble Wood to the east. The daily amount of aircraft stored in October was 330, from antiquated Hawker Harts to Bristol Beauforts, Blenheims and Hurricanes. Two runways were built between September 1941 and April 1942, the main one being extended in 1943 in order to accept heavy bombers and accompanied by the building of new taxiways. The station survived aerial attack in 1940-1, going on to play an important role in the readiness for D-Day with work on Horsa gliders and Typhoons in early 1944. The Fosse Way crosses the site.