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Roc Monitoring Posts, Mendip

Description: Roc Monitoring Posts

Grade: II
Date Listed: 21 August 2013
Building ID: 1415656

OS Grid Reference: ST5000450784
OS Grid Coordinates: 350004, 150784
Latitude/Longitude: 51.2540, -2.7178

Locality: Mendip
Local Authority: Mendip District Council
County: Somerset
Postcode: BA5 1JH

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Listing Text


Two Royal Observer Corps (ROC) monitoring posts: an Orilt type A of 1953 and an underground post of 1961.

Reason for Listing

The former 1953 Royal Observer Corps Orlit post and the 1961 underground monitoring post close to Westbury Beacon are listed at Grade II for the following principal reasons:

* Group value: the juxtaposition between the two structures reflects the technological developments in monitoring the threat of aerial attack during the Cold War;
* Architectural interest: although they have been built to standard military designs they are an architectural representation of the threat of nuclear attack during the Cold War; * Rarity: the Orlit Type A post is a relatively rare survival nationally.


The Royal Observer Corps (ROC) can trace its history back to the 1920s when a system of aircraft reporting was developed which formed part of the country's air defence. It was re-instated in1948 to meet the new threat posed by the Cold War. Orlit Posts, of which there were two types: A and B, were introduced in 1952 to provide shelter from the weather for observers and their equipment from where they co-ordinated reports on low-flying aircraft. Ministry of Defence records indicate that 413 were constructed in England, but by the late 1950s the development of faster jet aircraft made visual reporting ineffective. In 1957 the ROC became a major component of the United Kingdom Warning and Monitoring Organisation (UKWMO); its function to identify evidence of nuclear attack and to monitor radiation in the event of nuclear attack. Construction of a system of underground monitoring posts, accommodating up to four people, began in the late 1950s and was largely complete by 1965. Where possible, these monitoring posts were located on the sites of old visual reporting posts and they were evenly distributed across the country. Although some new posts were built in the 1970s, by 1968 the number of maintained posts was halved and, in 1991 with the end of the Cold War, the ROC was stood down and all posts were closed.

The ROC Orlit type A Post 57m north-west of Westbury Beacon is prominently sited on an eminence on the lip of a south-facing Mendip escarpment. The county Historic Environment Record states that an ROC post was established in 1938 some 700m to the south-east, and that it was relocated to its current position in November 1953, presumably when the Orlit post was erected in its current location near Westbury Beacon. This post was superseded by an ROC underground monitoring post sited slightly to the north in April 1961, the same month as the US failed invasion attempt of the Bay of Pigs, prompting the Cuban Missile Crisis. It remained operational until October 1968. It was surveyed (Subterranea Britannica) in 2001 and found to have been completely infilled with earth and rubble, although the surface features remained intact.

Due to the site's prominent location on the lip of a south-facing Mendip escarpment the area commands extensive views over the surrounding area. As a result it was selected in 1956 by EMI Electronics Ltd, an important supplier of radar and electronics systems who had a factory in Wells, to carry out full-scale tests on modelling low-level radar systems using English Electric Canberra and Vickers Valletta aircraft flying from Weston-super-Mare. Structures associated with this phase in the site's history include a small hut, a winch on a concrete base, and several other blocks of concrete. One mid-C20 photograph depicts an aircraft flying low over the area and the corrugated hut that stands close to the ROC posts. More recently, Thales UK has used the site for electronic equipment trials.



Orlit Type A Post, erected in 1953. One of two standard designs manufactured by Messrs Orlit Ltd for the Royal Observer Corps.

Description: it is constructed of pre-fabricated concrete panels that have been bolted together, with a concrete slab roof over the southern section; the rest of the structure originally had a removable corrugated steel roof cover but this is missing. It is rectangular on plan, measuring approximately 3.05m by 2.03m. At the south-east corner is a low entranceway (door is missing) which leads into the narrower, roofed section which was used as a shelter and store. To the right, a lower doorway provides access from the sheltered part into the former open observation area which housed instruments and charts. The interior has been completely stripped.


A Royal Observer Corps underground monitoring post of 1961. Built to a standard design of 1956 by the Air Ministry Works Department.

Description: the former monitoring post is set within a compound marked by concrete posts and a metal gate. It is built of reinforced concrete with a compacted earth covering and has a roughly rectangular plan. It takes the form of a low, elongated mound with a raised, concrete entrance hatch towards one (west) end and a smaller, raised concrete ventilator towards the other end. Between these two openings is a single metal pipe that was the mounting for the fixed survey meter probe. The mounting for the Ground Zero Indicator (a pinhole camera device for detecting the direction and altitude of nuclear explosions) is adjacent to the entrance hatch. The entrance hatch has been boarded over and the underground chamber has been completely infilled with earth and rubble.

The structures associated with the radar testing that was carried out in the area during the second half of the C20 which include which include a corrugated hut, a disused winch and several concrete blocks are not of special interest.

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