Royal Observer Corps (ROC) Orlit Type B visual observation post and an ROC underground monitoring station, 604m west-north-west of Lodge Farm


Heritage Category:
Listed Building
List Entry Number:
Date first listed:
Statutory Address:
604m WNW of Lodge Farm, Buckden, St Neots, Cambridgeshire, PE19 5UH


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Statutory Address:
604m WNW of Lodge Farm, Buckden, St Neots, Cambridgeshire, PE19 5UH

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

Huntingdonshire (District Authority)
National Grid Reference:


A Royal Observer Corps (ROC) Orlit Type B visual observation post, built between 1952 and 1956, and an ROC underground nuclear monitoring post, constructed in 1968.

Reasons for Designation

The Royal Observer Corps (ROC) Orlit Type B visual observation post, built between 1952 and 1956, and the adjacent ROC underground nuclear monitoring post, constructed in 1968, are listed at Grade II for the following principal reasons:

Architectural interest:

* although of a standard, functional design, their aesthetics and methods of construction illustrate Britain's rapidly evolving defence policy in response to changing threats to national security during the mid-C20;

* as rare and unusual Cold War military buildings that survive in a particularly good state of preservation.

Historic interest:

* the 'Orlit Type B' visual observation post symbolises the final days of the passive defence of the United Kingdom prior to the development of the hydrogen bomb, while the underground monitoring post demonstrates how technological advances in 'scientific' warfare influenced government defence policy over a relatively short period of time;

* their co-location reflects the continuing change in the role of the ROC and the changes in the types, and levels, of potential threat on a national and international scale during the mid-C20;

* as military buildings that stand testament to the work of the Royal Observer Corps, a volunteer force who were prepared to respond if the unthinkable happened and the United Kingdom was attacked from the air.


After the Second World War there was a general run-down of the early warning system, with most radar stations, along with military airfields, being dismantled or placed on care and maintenance. When it was confirmed that the Luftwaffe had ceased combat operations, anti-invasion defences were either cleared or abandoned while the Royal Observer Corps (ROC), a civil defence organisation formed in 1925 to visually detect, identify, track and report enemy aircraft over Great Britain, was stood down on 12 May 1945. This stand-down, however, was short lived, as the ROC was reformed on 1 January 1947 against a backdrop of increasing tension over Berlin, culminating in the Berlin blockade and subsequent airlift. At this time the threat from nuclear weapons was considered slight and, if it was an atomic attack, damage was expected to be on a limited scale similar to that experienced at Hiroshima in 1945.

In most cases the ROC returned to posts originally manned throughout the Second World War but found that many of the original timber structures were no longer fit for purpose. In early 1951, with nearly all of the 1,420 reactivated observation posts deemed unusable, the Air Ministry requested tenders from industry to provide the ROC with a purpose-built structure capable of sheltering its crews from the elements whilst also providing them with a stable, level platform from which to track the flight path of enemy aircraft. The contract was subsequently awarded to Messrs Orlit Ltd of Colnbrook, Buckinghamshire, a company specialising in the construction of precast concrete structures which included thousands of air raid shelters used during the Second World War. The manufacture of these new ROC posts, known as the Orlit Visual Reporting Post, or simply ‘Orlit Posts’, commenced in 1952 to a standard design in which precast concrete slabs were pinned or bolted together to form a rectangular-shaped structure measuring 3.05m x 2.03m in plan. Access was gained through a wooden door that led directly into a small covered area which, measuring 1.52m x 1.06m, functioned as an equipment store and a shelter in which the communications board (basically a telephone) was located. To the right-hand side of the entrance a sliding door in a dividing wall gave access to the observation platform which was open to the elements but covered with a corrugated metal roof when not in use. At its centre was a square, concrete plinth which supported the post plotting instrument (a standard optical sighting system used to determine the bearing and altitude of enemy aircraft). Messrs Orlit Ltd provided two variants of the structure: Type A, which was constructed directly onto a concrete base at ground level; and Type B, which was raised 1.82m above the ground on four precast concrete legs or, as in a number of cases, placed on top of pillboxes. The ROC post at Buckden, Cambridgeshire, is one of 206 Type B posts that were erected across England between 1952 and 1956, with a further 207 Type A posts also being constructed.

The concept of visual reporting by the ROC was short lived, as the greater speeds and altitudes attained by jet aircraft combined with the improved performance of radar led to a reduced requirement for their services by the RAF. Additionally, when, in late 1957, the Soviet Union launched the first true intercontinental ballistic missile, closely followed by Sputnik, it became evident that the threat of nuclear war had effectively made the ROCs aircraft reporting network redundant. In the same year, despite the operational life of the Orlit Posts being cut short, the ROC found a new role as a major component of the United Kingdom Warning and Monitoring Organisation (UKWMO). Set up under Home Office control, it had five main functions: warning the public of any air attack - conventional or nuclear; providing confirmation of a nuclear strike; warning the public of the approach of radioactive fallout; provision of a post-attack meteorological service for fallout prediction; and supplying the civilian and military authorities in the UK and neighbouring countries in NATO with details of nuclear bursts and with a scientific assessment of the path and intensity of fallout. The ROCs change in role from overground visual observation to nuclear monitoring brought with it a new range of structural needs as the Orlit posts erected between 1952 and 1956 offered no protection from the risk of nuclear attack. It was therefore decided that protected underground posts would be investigated to assist the ROC in undertaking their new role. In March 1956 a prototype underground monitoring post was erected at Farnham, Surrey, which with minor modifications, mainly to the hatch and air ventilation louvres, became the standard type for all subsequent posts constructed by local contractors under the supervision of the Air Ministry and ROC. After a site was chosen, which was usually an existing ROC visual observation post, a hole 2.7m deep was excavated to accommodate a reinforced concrete monocoque structure with a floor, walls and roof 30cm, 17cm and 30cm thick respectively. After a layer of bitumen was applied to waterproof the structure, soil was compacted over it to form a mound leaving the 4.6 m access shaft, doubling as an airshaft, protruding above ground, with a second air shaft positioned at the opposite end. The air vents were covered by downward-sloping louvres above ground and sliding metal shutters below ground to control air flow during contamination by radioactive fallout. The access block also contained the fixed point for a Ground Zero Indicator (an instrument that worked like a pin-hole camera to record the initial flash of a nuclear detonation on to a graded sheet of paper, allowing a fallout assessment to be reached) while two metal pipes, one 12.7cm in diameter and one 2.5 cm in diameter protruded from the roof and above the four-foot mound to be used with the Survey Meter Sensing Head and the Bomb Power Indicator Sensing Head respectively. Internally, at the bottom of the access shaft, there were two doors: one giving entry to a chemical closet, the other a large monitoring room measuring 4.6m x 2.3m which contained bunks, a desk, batteries for power and a hand operated ventilation system.

Underground monitoring posts were sited in clusters within a small geographical area, sufficient to permit the triangulation of plots, the results of which were to be reported to the semi-sunken Protected Group HQs and Sector Group HQs which superseded the wartime ROC centres during the early 1960s. The posts were designed to operate in a post-nuclear attack environment, and to be self-sufficient for an operational life of up to 14 days. In an ambitious programme 1,026 underground posts were built in England between 1958 and 1964 (1,518 nationally), though the construction programme continued until the early 1970s, ironically overlapping with the decommissioning in 1968 of a substantial number of the earlier posts due to the diminished risk of attack and to reduce defence expenditure. Some remained operational until the ROC was stood down in 1991. The underground monitoring post at Buckden was relatively short-lived, both opening and closing in 1968.


A Royal Observer Corps (ROC) Orlit Type B visual observation post, built between 1952 and 1956, and an ROC underground nuclear monitoring post, constructed in 1968. ROC ORLIT TYPE B VISUAL OBSERVATION POST

MATERIALS: it is constructed from prefabricated concrete panels with a concrete slab roof over the former equipment store and shelter on the west side; the former observation room is unroofed. PLAN: of rectangular plan, aligned east to west, raised 1.82m above the level of the ground surface on four concrete legs.

EXTERIOR: the Orlit Type B visual observation post, which follows a standard design by Messrs Orlit Ltd of Colnbrook, Buckinghamshire, is largely comprised of prefabricated concrete panels to all four sides. At the west end of the south side there is a doorway (door now missing) accessed by a concrete ladder with steel rungs and steel handrail.

INTERIOR: the doorway leads in to the former equipment store and shelter at the west end of the structure. Adjoining to its east, and divided from it by a concrete partition wall, is the former operation room which is unroofed. No fixtures and fittings of note are known to survive.


MATERIALS: of reinforced concrete with a compacted earth covering.

PLAN: it is rectangular on plan, aligned north-east to south-west.

EXTERIOR: the underground monitoring post follows the standard Cold War design and consists of a rectangular-shaped, reinforced-concrete bunker concealed beneath a low, elongated earthen mound. Protruding from the top of the mound at its north-east end is a raised, concrete, entrance hatch while a smaller, raised, concrete air vent rises at the south-west end, between which are two metal monitoring probes. Placed on top of the air vent adjacent to the entrance hatch is the mushroom-shaped mounting for the Ground Zero Indicator.

INTERIOR: the access hatch has a counterweighted steel door (now welded shut) to a 4.6m deep shaft containing a single metal ladder. At the bottom of the shaft there is a small chamber containing a store cupboard and chemical toilet and a door leading to the monitoring room which measures approximately 4.5m by 2.25m.


Books and journals
Lowry, B (ed), Twentieth Century defences in Britain. An introductory guide, (1995), 126-136
Information on the Buckden ROC Post from the Subterranea Britannica website, accessed 7 May 2020 from
Information on the history of ROC Orlit posts from the Royal Observer Corps Association Heritage website , accessed 7 May 2020 from
Information on the history of ROC underground posts from the Royal Observer Corps Association Heritage website , accessed 7 May 2020 from


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

End of official listing

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