Former 10 Group Royal Observer Corps Headquarters, Poltimore Park

Former 10 Group Royal Observer Corps Headquarters, Poltimore Park

This is a Royal Observer Corps Group Headquarters building, constructed in 1961–62 for the Home Office. The design was prepared by the Ministry of Public Works under the supervision of E.C. Godwin, Chief Superintendent for Drawings.

The building is constructed of rendered reinforced brickwork with a flat reinforced concrete roof fitted with steel blast doors and baffles. It has a sub-rectangular plan with an off-centre axial corridor that originally served accommodation rooms, offices, ablutions and latrines to its south-west side, and operations, GPO, plant and canteen rooms to its north-eastern side.

Externally, the building is a single-storey rendered reinforced structure spanned by a central square-plan upper storey, raised above the level of the flat asphalt-covered reinforced concrete roof. The roof is hidden behind a low parapet wall with flat concrete slab coping stones. Drain openings in the parapet permit rainwater to pass through to painted rectangular storm boxes and metal rainwater goods attached to the walls. The structure is devoid of any decoration apart from a stepped brick door surround and projecting brick piers on the corners of the main south-east elevation. The entrance is recessed to form a blast baffle with two steel blast doors at right angles to the main entrance. The door on the northern side allowed access to the particulate filter room, and the southern door allowed access into the main structure via an air-lock porch. A similar recessed doorway with a single steel blast door in the southern wall exists at the centre of the north-west elevation and served as an emergency exit.

Two ventilation flues and a cooling tower are built against the south-east elevation of the raised central upper storey. A triangular galvanised steel telescopic lattice radio mast is situated against the south-west wall. The walls have no fenestration; the only openings are for ventilation intakes and exhausts, all protected by steel plates. Those on the cooling tower have projecting galvanised steel cowls. Associated monitoring equipment such as the Atomic Weapon Detection Recognition and Estimation of Yield (AWDREY) sensor head has been removed from the roof of the cooling tower and the roof over the triangulation alcove of the operations room, although mountings remain.

The face of the north-east elevation breaks forward towards the southern end where the stand-by generator and plant room are housed, with an exhaust pipe from the diesel engine attached to the wall. The rendered surface was originally painted white to reflect heat generated by a nuclear explosion. Since 2006, the north-east and south-east elevations have been repainted olive green, and the plinth, door surround, brick piers and coping stones have also been painted black.

The Group Headquarters is entered from the blast baffle in the south-east elevation via a steel blast door leading into an air-lock at one end of the off-centre axial corridor. The corridor is flanked on one side by the stand-by generator, air-conditioning plant, GPO equipment rooms, operations room, kitchen and canteen. On the other side it is flanked by former domestic rooms including decontamination rooms, latrines, dormitories and officers' room. A stairway rises to the upper floor which contains an emergency water tank, wireless room and operations room gallery. The building was de-stored at the time of the Royal Observer Corps stand-down but retains a number of historic fittings and fixtures. An empty battery charging cabinet associated with the AWDREY equipment remains in the wireless room. The timber desk for the plotters, tellers and supervising officers forms a parapet around three sides of the gallery. Rotating Perspex-covered post plotting boards are attached to the desk on the northern side of the gallery, and a triangulation table with associated bomb tote boards is situated in the triangulation alcove in the northern corner. A timber partition wall clad with sound-deadening panels on the ground floor of the operations room defines the former teleprinter room. In the northern corner of the operations room is the dose-rate alcove, which retains its chart display board. A number of openings have been cut through the walls in the early 21st century and relate to the building's current use.

Associated with the Group Headquarters are two small detached structures: a diesel oil tank and an isotope store. The former is situated near the north-eastern corner of the Group Headquarters and is covered by a low rectangular and slightly domed concrete roof. The isotope store is situated near the north-west corner and was used for storing tins containing low-level radioactive sources for calibrating fixed survey meters. It is a rectangular, single-storey, rendered brick structure with a projecting flat reinforced concrete roof. The interior is protected by a baffle wall and is entered by an offset doorway. Bricks have been cut out in each elevation to give the store the appearance of a pillbox, and an open timber observation post has been built on the roof; these features are secondary and associated with its current use.