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List Entry Summary

This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.


List entry Number: 1395125



The building may lie within the boundary of more than one authority.

County: Greater London Authority

District: Hillingdon

District Type: London Borough


National Park: Not applicable to this List entry.

Grade: II

Date first listed: 26-Oct-2010

Date of most recent amendment: Not applicable to this List entry.

Legacy System Information

The contents of this record have been generated from a legacy data system.

Legacy System: LBS

UID: 508932

Asset Groupings

This list entry does not comprise part of an Asset Grouping. Asset Groupings are not part of the official record but are added later for information.

List entry Description

Summary of Building

Legacy Record - This information may be included in the List Entry Details.

Reasons for Designation

Yes list


Legacy Record - This information may be included in the List Entry Details.


804/0/10098 Building 23 at RAF Northolt 26-OCT-10

GV II Squadron Watch Office (building 23), 1928 constructed to design drawings 1072/26 and 784/27; late C20 alterations

MATERIALS: brick, in stretcher bond, steel trusses, slate roof

PLAN: rectangular building oriented west-east (designed with a footprint of 62 feet 6 inches long by 21 feet 10 inches wide).

EXTERIOR: Of permanent brick construction, with 11 inch cavity bricks laid in stretcher bond and painted green with a pitched slate roof which has a square chimney stack to the east. Off-centre main entrance in the south elevation with paired solid double doors and a date stone of 1928. Further ancillary entrances in the north elevation although these provided access to the A-type hangar which used to stand to the immediate north and to which it was connected by a now demolished corridor. An original and probably the main entrance in the west elevation has been blocked although its position remains evident. All glazing has been replaced with modern uPVC units (which are not of special interest). Historical photographs indicate that the majority of the windows were originally narrow multi-paned steel casements. Some have been lengthened and widened, others blocked although the lintels are still visible. A bay window, located on the south elevation and which provided an observation window for the Watch Office, has also been removed. Surviving original features, such as the mast supports above the west door.

INTERIOR: Original internal walls of 4 ½ inch brick. Historic features include tongue and groove panelling to dado level and some architraves. Roof space not inspected but original 20 foot span steel trussed with timber boarding are noted by Francis (2008, 114). Modernised internally: toilets to west, office to east and central social club hall with island kitchen. Inserted modern ceilings throughout. All modern alterations are not of special interest. The interior was originally subdivided to provide pilots' accommodation (a large rest room, locker room for two squadrons, WCs and heating room) and the watch office, the latter located at the east end of the building.

HISTORY: The outbreak of the First World War in 1914 and the inevitable rapid expansion of the Royal Flying Corps (the predecessor of the RAF) led to the selection and requisition of a number of new airfields in England. One such was at Northolt where 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. The airfield was laid out on a north-south alignment with the aircraft sheds aligned west-east to the north of the flying field. Further land was requisitioned as the airfield expanded. During the First World War Northolt was primarily a training airfield for pilots to be then deployed to the Western Front. Latterly it housed fighters to intercept Zeppelin airship bombing raids. Northolt became one of ten such 'air defence stations' surrounding London, this arrangement being known as the 'London Air Defence System'.

In the inter-war period Northolt functioned as both a military and civilian airfield with a flying school. The site was occupied by both a bombing and a fighter squadron as part of the 1920s RAF expansion plans, and considerable enhancement of the buildings took place. Further expansion, between 1928 and 1934, resulted in the 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 it is not clear how rapidly construction began. During the late 1920s to early 1930s Northolt took on the role of the transportation of senior government officials and the royal family, and this traffic increased when it became London's wartime airport. The station's most significant role at this time however, was its participation in numerous trials and air exercises associated with the development of the 'Dowding' system; the Integrated Air Defence System or IADS (see below).

Northolt was a key fighter station as part of 11 Group, RAF Fighter Command which covered the south-east of 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 a number of regional groups with a 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 the 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 the home of a number of air photographic reconnaissance detachments from RAF Benson charged with the gathering of imagery of key events in the battle for the liberation of north-west Europe, namely the D-Day landings, Arnheim and the Rhine crossings. Inevitably Northolt continued to expand during the Second World War, the most significant development being the construction of two concrete runways. The accommodation was enhanced also, but all post-1940 buildings were either of a temporary brick construction or were prefabricated.

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.

Details of the many units stationed here and the complex history and development of Northolt can be found in Francis's 2008 report.

BUILDING 23 (Squadron Watch Office) This building was the Squadron Watch Office and is therefore located adjacent to the hangars in the northern part of the site; on the airfield side of the former A-type hangar (building 6) to which it is was attached by a corridor (now demolished). It was built in 1928 according to a date stone on the building and was the fighter airfield version of the bomber station watch office but with accommodation for pilots on readiness alert as well as for the Watch Officer. As such it functioned as the equivalent of the modern air traffic control tower.

In the late 1930s building 23 played a role, albeit ancillary to building 27, in developing and then testing the Integrated Air Defence System, more commonly known as the 'Dowding System' after Air Chief Marshall Dowding. A triangle of key sites were involved: Bentley Priory, Stanmore, London, Fighter Command HQ; RAF Uxbridge, Group HQ for 11 Group Fighter Command (the country was divided into Groups) and then to Sector level (a subdivision of the groups) to RAF Northolt. 11 Group was the key Fighter Command Group as it included London and the South-east and was therefore in the front-line of enemy attack, hence why 11 Group was instrumental in devising an appropriate system of response. Each Sector (in this case 'Z' Sector) had a main fighter station (here RAF Northolt), which therefore had a Sector Operations Room (here building 27) to direct operations for its own and other fighter stations within the Sector. The Sector Operations Room was therefore in communication via telephone, teleprinter and wireless with other Operations Blocks, the Observer Corps and many other operations to allow the spotting and tracking of enemy aircraft and to co-ordinate an appropriate response. Building 27 was therefore the third stage in the chain of command, responsible for deploying and directing the Sector's squadrons to meet an enemy attack and the Squadron Watch Office (building 23) was the fourth and last element in the chain of command, initiated at Bentley Priory, whereby fighter crews were scrambled.

Building 23 served as the Watch Office and Aircrew Readiness room during the Second World War and thus had an undisputed role in the Battle of Britain. The building's role did change slightly, however, when building 187 took over the air traffic control functions thus reducing the watch office role here. In the early to mid 1950s the building, and the adjacent A-type hangar, were occupied by Fairey Aviation Ltd to assist in the production of the Gannet aircraft for the Admiralty. More recently, and until 2008, it was the No 32 (The Royal) Squadron aircrew crewroom.

SOURCES: Francis P, RAF Northolt: Historical Report & Building Survey), draft unpublished report (18 Feb 2008) for Defence Estates

Francis P, British Military Airfield Architecture: from Airships to the Jet Age, Patrick Stephens Limited (1996)

REASON FOR DESIGNATION: The Squadron Watch Office (building 23) at RAF Northolt is listed at Grade II for the following principal reasons: * Fabric: although the building has experienced alteration, it is the only pre-Second World War fighter watch office of its type to survive and thus is nationally unique; * Historic Interest (Air Defence System): A building of national significance in the development of the 'Dowding System' of Integrated Air Defence; the world's first such system which remains in use by the RAF today and which has been adopted by the majority of air forces around the world, representing the fourth level of IAD command; * Historic Interest (Fighter Command): the building from which RAF Northolt's pilots were scrambled during the Second World War and which evokes the contribution of the English, Polish and other squadrons of this station who made such a significant contribution to victory in the Battle of Britain in particular; * Group Value: visual and historic functional relationship with the Operations Block (building 27) and C-type hangar (building 5).

Selected Sources

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National Grid Reference: TQ 10055 85401


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