BUILDINGS 186, 187, 188 AND 189 (AIRCRAFT HANGARS), RAF HENLOW

Group of four paired aircraft hangars in line, built in 1918 by the War Office's Directorate of Fortifications and Works at RAF Henlow.

Construction comprises brick walls, buttresses, central piers and door 'pylons', with curtain walls of half-brick thickness in cheaper bricks. The roofs are softwood 'Belfast' trusses with corrugated steel door cladding and later profiled steel roofing, including lean-to units.

Each building is a double-span shed with a central row of brick piers, some later subdivided by brick or block partitions. The main spaces are otherwise single large working areas. On each longer side, low single-storey sets of stores or offices occupy the central bays, positioned outside the main volume. Buildings 186, 187 and 188 are each 16 bays and 52 metres long overall, with two clear spans of 24.3 metres each. Building 189 is 15 bays with two clear spans of 30.5 metres each; the designs are otherwise identical. The sheds align to the access road with a larger interval between 188 and 189 than between the first three.

Externally, all sheds follow a similar design with minor variations in attached outbuildings. Raking buttresses in dark red brick frame intermediate panels in lighter-coloured half-brick thickness, with broad 3-light casements at high level and smaller lights at low level. End bays lack windows and typically have small doors. All openings have flush concrete lintels. The low lean-to ranges run for 6 or 7 bays with small casements to most bays; on the airfield side some small sections are two storeys. The ends have full-width groups of 6-leaf sliding doors with corrugated cladding, below a continuous overhead box containing gear. Above each span is a low segmental tympanum with profiled sheeting. Originally the doors opened to brick 'pylons' outside the outer bays, but only one remains, on the outer end right of shed 189, built in red brick with three sets of paired piers carrying thin brick stiffening diaphragms with straight tops and segmental lower edges matching the internal construction. Between door groups on each span a large downpipe is carried in a recess to brick piers. Building 189 differs only in having wider main spans.

Internally, the main spaces have plain concrete floors, except where later modified for uses such as a gymnasium. Some later small office units have been inserted into the main spaces, which otherwise remain clear but contain a central row of paired brick columns. These are 2 bricks square with a clear gap and carry a longitudinal thin brick stiffening diaphragm on a segmental arch. The outer faces carry a concrete spreader corbelled in 3 courses to support a strut of 3 small scantling timbers spliced into the doubled bottom chord of Belfast trusses. These trusses, commonly employed from 1916 for aircraft hangars, have bearing ends plated in diagonal boarding to the point where the strut is taken in, then a close-set diagonal grid of small struts. The doubled upper chord in a flat segment carries close-set purlins and lined profiled roof sheeting. Vertical X-bracing runs between bays, with horizontal bracing in the bays adjoining the main doors.

RAF Henlow was established in 1917 as the Eastern Command Repair Depot. The War Office had issued instructions for constructing repair depots for each RFC Command, responding to the need to train personnel in rapid repair of aircraft and aero engines to sustain the war effort. Construction began in 1917, with substantial structures including these hangars dating from this period; the last huts from this era were demolished in the 1970s. The first service personnel arrived from Farnborough in May 1918, and limited output of Bristol Fighters and de Haviland aircraft was achieved by the Armistice. An extra area was added in early 1920, and in March that year Henlow became the Inland Area Aircraft Depot. It was one of very few airfields retained after November 1918, and in its role as the RAF's flight test and maintenance centre became vital to Sir Hugh Trenchard's newly independent air force. By 1924, when selected as permanent home of the School of Aeronautical Engineering, Henlow was producing 35 engines and 15 aircraft monthly. As a training base for skilled engineers and supplier of operational stations with latest aircraft, it became one of the RAF's largest bases alongside Cranwell, Halton and Uxbridge, accommodating some 7,000 personnel of various nationalities in 1940. The Officers' Engineering School taught basic engineering theory and management; one 1932 pupil was Frank Whittle. The Aircraft Riggers' School arrived after 1935. During the Second World War it functioned as one of the RAF's largest Maintenance Units, overhauling, repairing and modifying fighters and bombers from Spitfires and Typhoons to Lancasters. During the Battle of Britain in 1940, Hurricanes manufactured in Canada were crated in, assembled at Henlow and flown to front-line bases. In 1941, Operation Quickforce trained approximately 100 Henlow fitters to assemble Hurricanes on carriers bound for Malta. 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.

These five General Service Sheds form the most complete group of early buildings at Henlow and, despite some external alteration, comprise the most complete ensemble of hangar buildings on any British site for the period to 1923. The flying field has been partly developed by a golf course. The domestic site, located across the A6001 to the south of the technical group, retained an extensive group of married quarters in the Garden City tradition, alongside barracks and office buildings dated 1933-35 displaying unique architectural treatment for a military air base, with the officers' mess being the most consistently well-handled of these buildings.