Building 190 (Coupled General Service Shed), Raf Henlow

Building 190 (Coupled General Service Shed), RAF Henlow

A coupled maintenance shed completed in 1918 by the War Office's Directorate of Fortifications and Works, constructed to drawing number 2010/18. The building represents a significant development in RAF hangar design, being the only surviving example of a 100-foot span shed with metal trusses rather than wooden construction, marking the first move from timber to steel in this building type.

The structure is a double-span shed with gabled ends, measuring 52 metres in total length divided into 9 bays of 5.8 metres each. The two clear spans each measure 30.5 metres, with an internal clear height of 7.6 metres. Walls, buttresses, internal piers and door pylons are constructed in brick. The roof trusses are Dorman Long steel, which were supplied to the Air Ministry specification for 100-foot span aircraft sheds in 1918. The exterior is clad in corrugated steel sheeting, with roofs in later profiled steel.

On each long flank, broad raking buttresses flank half-brick curtain walls containing paired 24-pane steel casements arranged in a continuous clerestory strip. Three bays on each side of the centre bay have this arrangement, with similar low-level fenestration. Bays near the outer ends have some smaller lights. The two-storey lean-to units on both the southeast and field sides have small-pane steel lights, two to each level; those on the former boiler-house have been blocked and its stack removed. The gabled ends are sheeted above a continuous sliding track box.

The full height and width doors are substantial features, with eight leaves to each opening constructed from cross-braced steel framing exposed externally over corrugated cladding. At each outer end are the original brick pylons designed to take the stacked doors, each plain in construction but reinforced with a central pier and short returned stabilising ends that rise above the track box and eaves level.

The interior has a plain concrete floor with a central row of doubled brick piers linked at the head with brick diaphragms to a segmental arch along the line of the valley gutter. Horizontal bracing braces the bays adjoining the door openings, and light steel purlins carry the roof sheeting.

To each side of the main shed are lean-to units, some in two storeys, including a former boiler-house on the southeast side. Unlike the related Buildings 186–189 on the site, this example has retained its original external detail in window and door fitments, though it has lost its original roof lights and stack.

RAF Henlow was established in 1917 as the Eastern Command Repair Depot. The War Office had issued instructions for the construction of repair depots for each Royal Flying Corps Command in response to heightened awareness of the need to train more personnel in the rapid repair of aircraft and aero engines to sustain the war effort. Construction at Henlow, conveniently served by the Midland Railway, began in 1917, with more substantial structures including hangars dating from this period. The first service personnel arrived from Farnborough in May 1918, and limited output of Bristol Fighters and de Havilland aircraft was achieved by the Armistice.

An additional area was added in early 1920, and in March of that year Henlow became the Inland Area Aircraft Depot, making it one of a very small number of airfields retained for use after November 1918. In its role as the RAF's flight test and maintenance centre, it formed a vital element within Sir Hugh Trenchard's newly independent air force. By 1924, when selected as the permanent home of the School of Aeronautical Engineering, Henlow was producing 35 engines and 15 aircraft each month. As a training base for skilled engineers and a source of operational aircraft for squadrons, Henlow became one of the RAF's largest bases alongside Cranwell, Halton and Uxbridge, accommodating approximately 7,000 personnel of various nationalities by 1940. The Officers' Engineering School taught basic engineering theory and management; one of its 1932 pupils was Frank Whittle. The Aircraft Riggers' School was brought to the base after 1935. During the Second World War it served as one of the RAF's largest Maintenance Units, overhauling, repairing and modifying a wide range of fighters and bombers including Spitfires, Typhoons and Lancasters. During the Battle of Britain in 1940, Hurricanes manufactured in Canada were uncrated, assembled at Henlow and flown to front-line bases. In 1941, as part of Operation Quickforce, approximately 100 Henlow fitters were trained for the assembly of Hurricanes on carriers en route to Malta, with completed aircraft flown off deck. The Control Tower, manufactured from packing case material during this period, still survives. Parachute training, including for SOE officers, was another key function. In 1947 the School of Aeronautical Engineering became the RAF Technical College, relocating to Cranwell in 1965.

The five General Service Sheds form the most complete group of early buildings at RAF Henlow and, despite some external alteration, comprise the most complete ensemble of hangar buildings from the period up to 1923 on any British site. This particular 100-foot span shed, whose dimensions reflect the greater scale of military aircraft in late 1918, stands as the sole surviving example of this transitional design type with metal trusses.