Building 124 (Operations Block)

Sector Operations Block at Marne Barracks (formerly RAF Catterick), built in 1938 to designs by J.H. Binge of the Air Ministry's Directorate of Works and Buildings (drawing number 5000/137).

The building is constructed of reinforced concrete with Flemish bond brickwork cladding. Its roof structure comprises a thick-section concrete subroof slab supported by twenty large-scale rolled steel joists, with sand and shingle occupying the 4 feet 6 inches space between this and a thin-section concrete upper roof covered in asphalt.

The plan centres on a plotting room occupying the major space in a projecting taller block. Associated rooms include an operations room, meteorological office, battery room, ventilating plant room, searchlight room, teleprinter room, traffic office and receiving room.

Externally, a 9-foot-high reinforced concrete traverse wall with a maximum thickness of 17 feet surrounds the building, sloping to an angled earth bank. Two angled entrances feature shuttered concrete linings. Casements to the north have been blocked in. Cast-iron rainwater goods and ladder stairs to the roof are present.

Internally, the building retains original joinery including doors to message hatches, twin safes in the Code Room, cast-iron furniture to timber doors, electrical face plates, and ducting and grilles serving the air filtration plant. Steel outer doors are fitted. A raised platform runs along one side of the plotting room, providing a vantage point for viewing the centre of the room, where radio cross-bearings of Sector aircraft were translated into a map position and relayed to the operations room. Shuttered openings between the operations room and wireless cabinets allowed operators to maintain contact with sector fighters and switch the radio-telephone to controllers and their assistants as required.

Operations blocks for executive control of aircraft within fighter sectors first emerged in the mid-1920s and became especially significant during the Second World War. The 1920s designs were single-storey hipped-roofed structures, but designs developed from 1936 onwards, exemplified by this building and that at Debden in Essex, were protected against bomb blast with surrounding concrete walls and earth banks. The exterior was partly rebuilt in the 1950s as a War Room to counter nuclear flash and fallout.

This is the key operational building on the site, integral to the complex Fighter Command infrastructure established before 1940. From March 1936, Sir Hugh Dowding, in command of Fighter Command during the Battle of Britain, put in place an operational infrastructure that originated in his earlier Air Council position as Member for Research and Development. This system linked Chain Home radar stations (the first five operational in 1938 following development at Bawdsey) and Observer Corps posts by telephone and teleprinter to the Filter Room at Fighter Command Headquarters (Bentley Priory). Operations rooms controlled the Groups subdividing the country, with Air Vice-Marshal Keith Park commanding deployment within 11 Group from Uxbridge. Sector operations rooms on principal sector airfields such as this controlled individual fighter squadrons. Sector controllers retained executive authority over despatched aircraft until their return to base. From September 1939, Catterick played a vital role defending the north-east and North Sea convoys. During 11 Group's front-line role in the Battle of Britain, Catterick served as a rest station for fighter squadrons returning from the south-east. Catterick is the only fighter station in northern England retaining fabric recommended for listing as a consequence of English Heritage's thematic survey of military aviation sites and structures. Churchill wrote of such systems: "All the ascendancy of the Hurricanes and Spitfires would have been fruitless but for this system of underground control centres and telegraph cables, which had been devised and built before the war under Dowding's advice and impulse."