Building 5 At Raf Northolt

Building 5 at RAF Northolt is a C-type hangar constructed in 1934-5 to design drawing 2463/34, with late 20th-century and early 21st-century alterations.

The hangar is built with a steel frame, brick walls, and corrugated sheet cladding, all painted green. It has a rectangular footprint measuring approximately 90 metres west to east by 60 metres north to south, divided into eleven bays. Additional annexes extend to the south and north. In 2009 the hangar interior was subdivided into three sections.

The building has a multi-pitched roof with gables on the north and south elevations, creating the eleven-bay division. To the south, facing the airfield, a central flat-roofed annexe projects from the main structure. This southern annexe has a central double-storey section flanked by single-storey wings to west and east. The double-storey portion originally housed the squadron's commanding officer, as well as offices for the adjutant, sergeant major, a store, and a clerk's office. The western wing contained offices for two flight commanders, two stores, and an airmen's rest room. The eastern wing accommodated pilots' locker rooms, air gunners' lockers, two stores, a further flight commander's office, and a clerk's office. The windows throughout the annexe have been replaced with modern double-glazed units. To the north is a further single-storey flat-roofed annexe, also with replacement windows. All replacement windows are not of special interest. The northern annexe housed technical functions: west of a central covered way were a battery charging room, boiler house, detail room, wireless telegraphy workshop, store, and toilets. East of the covered way were the gun cleaning room, workshop, and a paint and dope store (dope being a plasticised lacquer applied to aircraft fabric). Substantial aircraft sliding doors face west and east. These steel-framed doors are in six leaves, opening fully with three leaves to either side supported on projecting door gantries.

Inside, a steel structure of lattice wall stanchions at 25-foot centres supports the main roof girders. Large glazed windows at clerestory level along the long north and south elevations light the interior. Either side of each window are piers dividing the long elevations into the eleven bays. In February 2009 internal dividing walls of steel pier construction were being erected to divide the formerly single interior space into three sections: an eastern storage bay, a central spray shop, and a contingency space to the west. These modifications are not of special interest. The roof consists of steel trusses with cross bracing and is understood to have timber purlins and boarding clad with asbestos slates.

The hangar was constructed as part of the mid to late 1930s expansion scheme. An estimate for the works, totalling £21,000 for a 200-foot shed, was submitted in 1934. The final design of 1935 was for a 300-foot shed as it was intended to house two squadrons. It was designed by the Ministry of Works (with B. C. Jacklin known to have been involved) to accommodate both single-seater fighter aircraft and space for aircraft development. It was first occupied in November 1938, providing a completion date. In form it resembles a design more commonly associated with bomber airfields, with the squadrons' accommodation incorporated in the hangar annexes.

RAF Northolt itself was established in 1914 during the First World War expansion of the Royal Flying Corps. Land was acquired by the War Office from February 1914 with the landing ground operational by the following month, although accommodation was initially temporary and basic. During the First World War Northolt was primarily a training airfield for pilots destined for the Western Front, and latterly housed fighters to intercept Zeppelin airship bombing raids as one of ten air defence stations surrounding London in the London Air Defence System.

In the inter-war period Northolt functioned as both a military and civilian airfield with a flying school. It was occupied by both a bombing and a fighter squadron as part of the 1920s RAF expansion plans, with considerable enhancement of the buildings. Further expansion between 1928 and 1934 resulted in construction of further buildings including the Pilots' Room and Watch Office (building 23). The Operations Block (building 27) was also completed by 1928, having been designed in 1924 although the construction timeline is unclear. During the late 1920s to early 1930s Northolt took on the role of transporting senior government officials and the royal family, traffic that increased when it became London's wartime airport. The station's most significant role at this time was its participation in numerous trials and air exercises associated with the development of the Dowding system, the Integrated Air Defence System.

Northolt was a key fighter station as part of 11 Group, RAF Fighter Command, which covered south-east England and was commanded by Air Chief Marshall Sir Keith Park. (Fighter Command had been established in 1936 to organise the country's fighter stations in regional groups with central command based at RAF Bentley Priory. Other Commands covered Bomber, Transport and Training.) Northolt, acting in association with Uxbridge and RAF Bentley Priory, was very much in the front line during the Second World War. The station's fighter squadrons played a key role throughout and were notable for their success in destroying enemy aircraft with limited losses during the 1940 Battle of Britain. Northolt was the first airfield to house operational Hurricanes and was also home to Polish Fighter Squadrons. In 1943 it became the main terminal for RAF Transport Command but also remained a fighter station until March 1944. In the same year it became home to air photographic reconnaissance detachments from RAF Benson charged with gathering imagery of key events in the battle for the liberation of north-west Europe, namely the D-Day landings, Arnhem and the Rhine crossings. Northolt continued to expand during the Second World War, the most significant development being construction of two concrete runways. Accommodation was also enhanced, but all post-1940 buildings were either of temporary brick construction or were prefabricated.

Throughout the Second World War this hangar housed Churchill's personal aircraft in which he flew to many important meetings of the Allied leaders. During 1946 the hangar was partly allocated to British Overseas Airways Corporation and partly to RAF Transport Command. In the early to mid 1950s the hangar was occupied by the RAF's VIP Flight.

In 1945 the government decreed that Northolt and Croydon should operate as London's airports. Broadly Croydon was used by UK airlines and Northolt by European Services and foreign airlines. By 1952 Northolt had become the busiest airport in Europe but from then on, as the new airport at Heathrow became gradually operational, more civilian flights transferred there such that Northolt could revert to the RAF by October 1954, and by October of the following year all civilian flying ceased. The site remains an operational RAF station with its VIP transportation role still a significant function.

The building represents the earliest 1934 form of C-type hangar design, a hangar type that became the most commonly built and successful RAF hangar. It is one of only five of this early design surviving nationally. It is the only surviving large hangar at RAF Northolt which was operational during its key Second World War action. It has visual and historic functional relationship with the Operations Block (building 27) and Squadron Watch Office (building 23, which served the now demolished A-type hangar).