Bofors Tower, c1940.
Reason for Listing
A Bofors gun tower, an outlying anti-aircraft defence to the RAF Kenley Fighter airfield, is listed at Grade II for the following principal reasons:
Form & intactness: a good, intact example of a tower of reinforced concrete pier form, the operation of which is legible through its fabric;
Rarity: one of only a handful of known examples of this type of site nationally;
Historic interest: an integral part of the nationally important RAF Kenley Fighter airfield associated with the Battle of Britain;
Group value: with the designated fighter pens, Officers’ Mess and NAAFI at RAF Kenley.
Kenley was first used as a Royal Flying Corps aerodrome in 1917 although the buildings associated with the grass flying field have all now gone. An Act of Parliament in 1939, following agreement to provide all-weather runways and perimeter tracks for critical fighter stations prone to waterlogging, led to the expansion and rebuilding of RAF Kenley to provide two 800 yard (732m) runways which were completed in December 1939. (Its runway was subsequently extended by a further 200 yards (183m) in 1943 to allow larger aircraft to land.)
In 1940 Kenley’s defences were considerably strengthened with dispersed fighter pens, air raid shelters, machine gun posts and anti-aircraft defences and it is to this phase of development that the Bofors Tower relates. By April 1940 all 12 fighter pens (the ten surviving of which are scheduled as ancient monuments) had also been completed and the station was fully operational. The aircraft based at Kenley formed part of 11 Group, a division of Fighter Command covering London and the south-east, and it was able to house two squadrons of twelve aircraft in each fighter pen and a further squadron dispersed on open hard standings.
Kenley was subjected to some of the most sustained attacks on a fighter station by the Luftwaffe in 1940. On 18th August one raid led to the loss of three personnel, three hangers and two aircraft; photographs of an attack on a fighter pen appeared in the German Der Adler magazine. On 30th August 39 personnel were killed and 26 wounded and on the following day the Operations Block was damaged. The scars of these raids can still be read in the form of post-war repair work to the Officers’ Mess, prominently sited on the west side of the aerodrome, and which now stands as the most impressive surviving building from the rebuilding of the station between 1931 and 1933 (and is Grade II listed). Despite these sustained raids, and as a tribute to the design of the airfield with its hardened fighter pens and anti-aircraft defences, Kenley continued to launch fighter aircraft and played a vital role throughout the Battle of Britain and the later London Blitz. The last surviving hangar and the control tower were destroyed by fire in 1978 and the Sector Operations Block was demolished in 1984.
The Bofors Tower is located on land that was part of the Essendene Estate which, during the war, provided accommodation for the Canadian Army. The tower is an outlying anti-aircraft defensive structure associated with the RAF Kenley airfield (which is approximately half a mile to the north-west of the tower). According to Newall (2002b, 42) a similar pair of towers were erected at the same time to the west of RAF Kenley on Coulsdon Common but were demolished in 1946.
Light anti-aircraft (LAA) guns needed to command a good, if not 360 degree, field-of-fire in order to be effective. Many such guns were moveable but some were permanently mounted in ground-level purpose-built emplacements. Roof-top sites were increasingly favoured as they allowed the required clear field-of-fire. In November 1939 it was already apparent that some Vulnerable Points intended to be defended by the new 40mm Bofors LAA guns, lacked the local topography to elevate the guns to maximum effect. This led the War Office to begin to design, from mid-December 1939, an elevated Bofors gun-platform. Early designs included platforms of different heights (from 10 feet to 30 feet with variants at five feet intervals) which could be erected to suit the local topography. This allowed a stepped arrangement whereby the gun predictor could be mounted on a separate platform from the gun and slightly above it, while the gun tower housed the gun and also four ready-ammunition lockers. Dobinson (2001, 179) suggests that prototypes were erected in early 1940 but were soon superseded, by late summer, by a simpler steel-framed design. Historical documents suggest a form of scaffolding-type tower arrangement but where very tall towers were needed concrete continued to be favoured for reasons of stability. In February 1941, 53 Bofors towers had either been built or were under construction (only half with guns) and by January 1942 the number had risen to 81 either complete or under construction (Dobinson, op cit). Although only two designs are known; the concrete version from the Directorate of Fortifications and Works (DFW) 55087, and the steel version (DFW 55463) there may have been other Air Ministry variants (Dobinson 1996, 166).
Kenley gained four 40mm Bofors guns as part of the strengthening of its defences in the early 1940s. Although the precise date they arrived is not known, Newall (2002b, 42) cites minutes of 16 July 1940 which refer to ‘Defence works which have been carried out at Coulsdon Common…’ and ‘the erection of Anti-Aircraft gun positions’ which seems to provide a terminus post quem. Whether these were all initially tower mounted is not clear but seems likely. There are also records of Bofors guns at Kenley engaging and shooting down enemy aircraft in August 1940 although it cannot be certain that these relate to this particular tower.
MATERIALS: Reinforced concrete
The Bofors Tower is located south of Burntwood Lane in a pasture field. It comprises two elevated reinforced concrete platforms located immediately adjacent to each other. A Bofors anti-aircraft gun would have been mounted on one platform and its range predictor (to calculate enemy aircraft speed and height and thus ensure the accuracy of the gun) on the other so that the gun’s recoil did not disrupt the predictor. The rationale for erecting Bofors guns and their ancillary equipment on towers was to elevate them above the surrounding landscape and enable a 360 degree field of fire against low-flying and fast-moving enemy aircraft.
The tower is built of reinforced concrete and is constructed of concrete piers and cross-braces rising in three sections to the gun and predictor platforms. The piers appear square in section and the cross-braces are reinforced at the joins. Aerial photographs offer an opportunity to view the platforms from above: combined they have a broadly rectangular footprint although with a small projection at the north-west corner. The platforms were accessed by ladder stairs which were removed soon after the war although the platform projection and a further projecting piece of concrete on the west side at high level suggests the position of part of the stairs. It appears that the eastern platform was the gun platform as a central circular mark, which appears to be the ghost of the gun holdfast, is visible on aerial photographs.
Source: English Heritage
Listed building text is © Crown Copyright. Reproduced under licence.