Royal Observer Corps Monitoring Post Royal Observer Corps Monitoring Posts are underground structures all over the United Kingdom and Northern Ireland , constructed as a result of the Corps ' nuclear reporting role and operated by volunteers during the Cold War between 1955 and 1991 . In all but a very few instances the posts were built to a standard design consisting of a 14 - foot - deep access shaft , a toilet / store and a monitoring room . The most unusual post was the non - standard one constructed in a cellar within Windsor Castle . A third of the total number of posts were closed in 1968 during a reorganisation and major contraction of the ROC . Several others closed over the next 40 years as a result of structural difficulties i . e . persistent flooding , or regular vandalism . The remainder of the posts were closed in 1991 when the majority of the ROC was stood down following the break - up of the Communist Bloc . Many have been demolished or adapted to other uses but the majority still exist , although in a derelict condition . Construction . The first prototype post was built at Farnham , Surrey , in 1956 and on 29 / 30 September of that year a trial was conducted to ascertain the usefulness of the underground posts . Of the two crews of four personnel engaged in staffing the post during this trial , the second group of four , two ROC and two Home Office Scientific Advisory Branch , were sealed inside with rations bedding and barrack equipment . With a few minor changes , mainly to the hatch and air ventilation louvres , the posts were built as per the prototype . The protection provided by the concrete roof and compacted earth mounded above the post was estimated to reduce any external nuclear radiation by a factor of 1 , 500 : 1 . Construction of the original 1 , 563 posts was overseen by the Air Ministry Works Department and the ROC and undertaken by local contractors . Once a site was chosen ( usually the site of an aircraft observation post ) a hole approximately 9 feet deep was excavated . Within this hole a monocoque structure was cast using re - enforced concrete with a floor about twelve inches thick , walls about seven inches thick and a roof about eight inches thick . The whole structure was then bitumen ' tanked ' for waterproofing purposes . Soil was compacted over the structure to form a mound leaving the access shaft , doubling as an airshaft , protruding above ground . At the opposite end of the building a further air shaft was formed . Two metal pipes , one 5 inches in diameter and one 1 inch in diameter protruded from the roof and above the four - foot mound to be used with operational instruments . The air vents were covered by downwards sloping louvres above ground and sliding metal shutters below ground to control air flow during contamination by radioactive fallout . The Home Office wanted 100 posts built in the first year ( 1957 ) and 250 a year thereafter . By mid - 1958 only 94 posts had been handed over to the ROC with 110 under construction . The cost of building the underground posts was approximately £1000 , but rose to nearer £8000 in some instances . Restorations . Today most posts lie derelict and abandoned . Approximately half of the posts built have been demolished , either on stand down by the ROC or by private owners in subsequent years . One post , in York , has been incorporated in to a house and forms a handy cellar . A small number of posts have been purchased and either restored to how they were and usually opened as museums with guided tours by prior arrangement . One such post is the former 20 Group York , 37 Post ( Brandsby ) post north of York , which has been painstakingly restored to how it was in the final summer of operation in 1991 . It is the nearest restored Monitoring Post to the only restored ROC Group Control in Britain , HQ 20 Group York , Shelley House at Acomb , York . Other known restored posts include Skelmorlie , Scotland , Veryan , Cornwall , Skipsea , Yorkshire , Rushton Spencer , Staffordshire and Portadown County Armagh . Several more are planned or are under development . See also . Operational instruments of the Royal Observer Corps