Type E Hangars, Site C

Two aircraft storage hangars built in 1938-39 to Air Ministry Directorate of Works and Buildings drawing Number 7305/37. The hangars are constructed with reinforced concrete ribs supporting concrete slab roof panels curved to follow the arc of the frame, covered with profiled steel sheeting. The end walls are in-situ concrete.

Plan and Form

The two hangars are identical and positioned at right angles to each other, north of where the two runways cross. Each forms a plain rectangle with internal dimensions of 300 feet by 167 feet and a maximum height of 36 feet (91.4 by 50.8 by 11.1 metres). They create low parabolic vaults that spring from ground level, with wide doors at each end. One end of each hangar has two small annexes flanking the door opening, one containing the boiler room. Small doors in the end walls provide personnel access.

Exterior

The hangars present a broad, completely unbroken expanse of corrugated steel sheeting covering the low-profile parabolic forms. The inner ends have a pair of steel doors in a near-square opening. To the left stands a square stack rising just above parapet level and a projecting annexe with a monopitch roof. To the right is a similar but smaller unit. Both these elements are set at right angles to the diaphragm wall with roofs sloping away from the centre.

At the outer ends, three pairs of high steel doors open within a broad rectangular concrete frame that extends about two-thirds of the total width and rises above the parabolic parapet in the outer sections. This 'gantry' is planted on the outer face of the concrete diaphragm wall, and above its centre sits a square ventilator with sloping external cheeks. The parapets to the end walls carry bold modelled parapets and are flared out at the bottom. A continuous wide concrete trough-gutter runs at ground level along each side.

Interior

The floor is smooth-finished concrete. The structure consists of a series of rectangular-section concrete ribs at 13-foot (4-metre) centres, carrying cast concrete roof slabs, with smaller longitudinal square-section purlins. The ribs are chamfered back at floor level so the entire floor surface remains unencumbered. Ribs and ceiling soffits are totally clad in fibreboard. Continuous longitudinal steel rails—two single and four doubled—are suspended from the structure.

Historical Development

This form of hangar evolved from the earlier 'Lamella' type (present at Sites A and B at Kemble), with the same overall dimensions but constructed entirely in concrete with simple ribs set in parallel rather than using the 'network' principle of the German prototype. Originally the roofs were covered in earth finished with turf, which provided extra protection against bomb blast and excellent camouflage from above. Turf-covered versions may be seen at Hullavington airfield in Wiltshire, about 10 kilometres south of Kemble.

The construction method involved concrete arched-shaped ribs at 11-foot and 13-foot centres with cross-beams, the whole framework covered with slightly curved pre-cast concrete slabs cast in-situ using mobile formwork inside the shed, shuttering on the outside, and electric vibrators. For concealment from above, the entire structure was covered with earth and turf. End walls consist of reinforced concrete columns and beams infilled with 5-inch thick concrete. Steel doors at either end gave a clear opening of either 40, 60, or 80 feet. To minimise condensation, the interior was clad with fibreboard and parallel runways were fitted longitudinally for storing aircraft in the tails-up position.

Problems were encountered keeping the earth covering in place, but this was largely overcome using small pyramid-shaped blocks of concrete fixed onto the vibrated concrete slabs. These contained steel rods to which steel ropes were attached to form a grid pattern. Soil was then built up flush with the ropes, which also acted as guides so soil could be evenly distributed over the whole shed, avoiding unnecessary stress to the structural members. Galvanised wire was then laid and secured to the guide ropes, over which was laid a thin layer of more soil and finally a layer of turf, giving a total covering of nine inches.

Context and Significance

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 (ASUs) planned and built by the Air Ministry for the storage of vital reserve aircraft in the period 1936-1940. The ASUs 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 ASUs 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 affected hangar design in ASUs through 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 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. 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 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 and C) and Type E uses ribs of small-section steel to support concrete slabs curved to the arc of the frame (Site C). 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 of airfield landscape, is certainly unique in a British context, and no such group survives in France or Germany.

Operational History

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 to accept heavy bombers and accompanied by the building of new taxiways. The station survived aerial attack in 1940-41, going on to play an important role in the readiness for D-Day with work on Horsa gliders and Typhoons in early 1944.