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World War II Bofors Gun Tower and Ancillary Building, Hillingdon

Description: World War II Bofors Gun Tower and Ancillary Building

Grade: II
Date Listed: 15 May 2013
Building ID: 1414202

OS Grid Reference: TQ0994186829
OS Grid Coordinates: 509906, 186817
Latitude/Longitude: 51.5695, -0.4156

Locality: Hillingdon
County: Greater London Authority
Postcode: HA4 6AH

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Listing Text


World War II Bofors gun tower and ancillary building (possibly either a magazine or a shelter for the off-duty gun crew). Tower built c1940 to Directorate of Fortifications and Works (DFW) design 55087.

Reason for Listing

The World War II Bofors tower and ancillary building at Ruislip Manor Sports Club, built c1940, are listed at Grade II for the following principal reasons:
* Architectural form and intactness: a well surviving example of a reinforced concrete Light Anti-aircraft (LAA) gun tower, where its original operation is clearly legible through its fabric and unusual for the survival of an associated ancillary building;
* Rarity: one of only a handful of known examples of this type of site nationally;
* Historical interest: as a reminder of the air assault on London during World War II and for its likely association with RAF Northolt, a key fighter station during the Battle of Britain.


Light Anti-aircraft (LAA) sites were designed to provide protection against low-level air attack and nearly 1,250 LAA gun sites are recorded as having been built in Britain during World War II. The gun tower at Ruislip conforms to type DFW 55087. This design was issued by the Directorate of Fortifications and Works (DFW) at the end of 1939 with the earliest examples constructed during the first half of 1940. The tower was designed to raise a 40mm Bofors anti-aircraft gun and its operational equipment above surrounding obstacles in order to achieve an all-round field of fire. The concrete frame could be built to various heights according to need. By the summer of 1940 this design was being replaced by a simpler, steel-framed type. Around 80 examples of concrete-framed Bofors towers are thought to have been built in Britain. Ammunition magazines for the towers were built to differing specifications, often in adapted Anderson shelters, and few have survived. Indeed ancillary buildings of any function associated with Bofors towers are rare survivals.

At Ruislip, the tower was built either to protect the approaches to RAF Northolt, located 1.3km to the south or, possibly, an underground munitions depot at Ruislip Manor.


MATERIALS: reinforced concrete frame and platforms with brick infill.

DESCRIPTION: the tower, located at the north-east corner of the football ground, comprises two elevated platforms, approximately 5m high, located immediately adjacent to each other, leaving a narrow gap between them at platform level. The Bofors gun would have been mounted on the larger (north-western) platform and its range predictor (to calculate enemy aircraft speed and height and thus ensure the accuracy of the gun) on the smaller (south-eastern) one. This was so that the gun’s recoil did not disrupt the predictor. The raised hexagonal concrete mount for the Bofors gun is located in the centre of the gun platform. It is not known whether the steel holdfast frame survives.

The concrete frame of the platforms has full-height brick infill which has been extended to the rear (north-east) of the range predictor platform to form a concrete-roofed extension. This had a large opening in the south-eastern elevation, now blocked. Small openings with concrete frames are set high in the brickwork to provide ventilation. There is another large blocked opening in the north-east wall of the infill of the gun platform.

Internally, the range predictor platform has two floors and the gun platform just one. An external concrete staircase along the south-east elevation provides access from the ground floor to the first floor ammunition store in the range predictor tower (the entrance door in the south-west elevation is bricked up) and then up to the roof. At ground level, the range predictor tower has a pillbox-type room with a low ceiling.

The gun platform has a single high-ceilinged room on the ground floor. This room and that in the outshut at the rear of the range predictor platform would have housed the operations room and generator. Between the two platforms is a full-height ‘entrance lobby’ with an entrance in the south-west elevation. The brick infill to create this lobby is presumably post war as it would have interfered with the deliberate separation of the two platforms.

25m to the north-east of the tower is a single-storey, rectangular plan building built of brick with a flat reinforced-concrete roof. It has an entrance on its south-east elevation and a narrow, triple-light metal framed window set high up in the opposite elevation. This was probably either a magazine for the Bofors gun or a shelter for the off-shift gun crew, and is included in the listing.

Listed building text is © Crown Copyright. Reproduced under licence.