Duxford: Building 79 (Hangar 4)

Aircraft hangar built in 1917–18 to War Office Directorate of Fortifications and Works Drawing Number 332/17, designed by Lieutenant-Colonel BHO Armstrong of the Royal Engineers. This is the westernmost of a group of three identical contemporary hangars standing in-line on a north-east to south-west axis on the north side of the airfield. The annexes were rebuilt and altered in 1935.

The hangar comprises paired sheds, each of 100 feet span and 25 feet clear height, with full-height and full-width sliding and folding doors at the east and west ends. The 15-bay north and south sides have an overall length of 170 feet and feature brick buttresses arranged at 11 feet 4 inch intervals supporting Belfast roof trusses. Lean-to annexes adjoin the north and south sides.

The east and west openings are fitted with Esavian sliding and folding doors with diagonal timber boarding running to an overhead track, with a deep apron above extending the full width of the hangar to compact brick pylons at each end. Wicket doors within the Esavian doors provide personnel access.

The north and south walls have raking buttresses carried up to the eaves soffit, with half-brick curtain walls between. Each end bay is plain. The remaining 13 bays contain a full-width steel casement window in 27 panes set as a high clerestory; alternate bays also incorporate a six-pane pivoted opening section. A deep apron band sits above these windows. At each end the door pylons form square shafts.

The roofs are profiled steel in flat segmental form, with continuous ridged patent glazing roof lights to the central 13 bays and a line of patent glazing on each side of the central valley. The eaves have a plain painted fascia with gutter. Above the horizontal apron to the door track is a flat segmental pediment to each shed with close-set vertical joint divisions to metal cladding and a wide central ventilation louvre.

The southern annexe, dating from 1935, is steel-framed with brick cladding and corrugated steel sheet roof. Its central five-bay section is two storeys with small-pane steel casements, mainly three-light with transom on the ground floor and two- and three-light with transom on the first floor. The five-bay single-storey range on the left has single two-light casements and two three-light casements, all with transoms and small-pane glazing, plus single and double wooden doors with small-pane top lights and fanlights. The right-hand range is 4½ bays with five small-pane steel casements: two-light windows with transom to odd-numbered bays and three-light windows with transom to even-numbered bays. Odd-numbered bays also have half-glazed wooden doors. The final ½ bay also has a half-glazed door.

The northern lean-to annexe was originally six bays but was extended by four bays in 1935. It has eight steel casement windows in 12 panes, each incorporating a four-pane pivoted opening section, with metal security grilles covering the four windows at the right-hand end. Three wooden double doors are at the left-hand end.

Interior: the paired sheds have a central row of brick oblong piers with narrow central openings to arched heads. Moulded stone corbels on each side carry the roof strutting. Running between the piers to support the gutter and provide stiffening is a series of diaphragm walls, one brick thick, on flat segmental arches.

Each bay is divided by wooden-latticed Belfast roof trusses spanning from the central row of piers to the buttresses in the outer walls. All trusses are whitewashed, with a flat bottom chord and bowed upper profile formed in a series of straight members. Truss members are small-section softwood with doubled main members sandwiching a close-spaced diagonal grid infill. At end supports the trusses are strutted to shaped stone corbels, with the knee area strengthened by diagonal close-boarded sheeting. Five sets of simple cross bracing run longitudinally, with diagonal sheathing on small purlins carried to the roofing. The end bays have extra horizontal bracing to the bottom chord.

A painted sign on the south wall reads "GAUNTLET ENDURANCE / AT NORMAL CRUISING SPEED 2 HOURS 30 MINUTES", dating from around 1935 and referring to the endurance of the Gloster Gauntlets used by 19 Squadron.

Hand-painted swastikas dating from the Second World War appear on brick walling in one of the offices in the southern annexe. They were painted by ground crew from the US 78th Fighter Group to represent the downing of enemy aircraft.

Materials: brick buttresses, curtain walls and internal piers (all painted), and timber roof trusses covered with profiled steel sheeting. Annex roofs are corrugated steel sheeting.