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The Cold War, which developed between the Soviet Union and the western allies after World War II, had a major effect on both Britain's defence policy and the wider society in general in the second half of the 20th century. When Russia first detonated a nuclear bomb in August 1949, the threat posed by nuclear weapons was taken very seriously. In 1954 it was shown that any debris thrown up by a nuclear explosion would be carried by the wind to settle back to earth as an extended plume of radioactive fallout and that large numbers of lives could be saved if people were warned to take cover until radiation levels had dropped by a sufficient amount. When the Royal Observer Corps' task of fallout monitoring was first conceived, only a small number of relatively low powered nuclear devices were expected to be dropped on Britain in any attack, such as that threatened by the Soviet Union during the 1956 Suez Crisis. Following the arms race through the late 1950s and 1960s, with the development of more powerful weapons with multiple warheads, it is now uncertain how useful the Royal Observer Corps would really have been in the face of a full scale nuclear attack. However perhaps more important was the Royal Observer Corps's role in the propaganda war against the Soviet Union, giving out the message that organisationally Britain would survive a first nuclear strike, thus giving more weight to Britain's own nuclear deterrent. On the Home Front, the Royal Observer Corps, a civilian organisation whose mainly volunteer force numbered around 17,000 in the mid-1960s, helped to maintain public morale in the depths of the Cold War. Royal Observer Corps Group headquarters were thus a key component of Britain's response to the Cold War. They are a very good example of the design principles behind 1950s-1960s protected installations and an important monument of Britain's post World War II history. Of the ten semi-sunken and nine surface built group headquarters originally built in England, the example at York is the only one known to retain nearly all of the equipment which was in use when it was stood down in 1991, most of which had been installed since the 1960s. The surface built examples at Winchester and Colchester retain some internal fittings, one other semi-sunken headquarters, at Yeovil, may also include internal equipment. It is not known if the Group Headquarters at Leeds, which was closed in 1968, has been cleared. The rest of the group headquarters have either been demolished or cleared and adapted for reuse. The example in York is thus considered to be one of the best surviving examples of either surface built or semi-sunken Royal Observer Corps group headquarters in the country.

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The monument includes a semi-sunken earth covered headquarters building, together with its internal and external fixtures and fittings. It lies to the rear of Shelley House on Acomb Road and formed the headquarters of No.20 Group, Royal Observation Corps from 1961 to 1991. The Royal Observer Corps was a uniformed civilian organisation which had a mainly volunteer force, originally for spotting and tracking enemy aircraft over Britain. In 1955, the Corps was given the task of reporting the locations of nuclear explosions and the tracking of subsequent plumes of radioactive fallout in the event of nuclear war. Between 1957 and 1965 an extensive network of 1561 underground monitoring posts were constructed (985 in England) organised into regional groups, each reporting to a group headquarters which analysed and passed on data to civilian and military authorities. Most of Yorkshire formed No.20 Group with its headquarters at York. The semi-sunken headquarters building which forms the monument was opened on 16th December 1961, replacing a World War II surface building near to York racecourse. It was one of 25 purpose built structures constructed in 1960 to 1965, with 19 being in England. Half of these were surface built and half semi-sunken following a standard 1958 Air Ministry specification which was designed to provide protection for a staff of around 60 men and women from the radiation and blast effects of contemporary nuclear weapons. The headquarters is known to have been on alert in October 1962 during the Cuban Missile Crisis and its alert status subsequently varied according to the international situation at the time. In the budgetary cuts of 1968, a large number of monitoring posts nationally were decommissioned, although the York Group Headquarters gained responsibility for most of the posts in No.18 Group following the closure of the headquarters at Leeds. The headquarters were modified in the late 1970s to early 1980s with the removal of part of the earth banking for the addition of a telescopic radio mast adjacent to the main entrance and the replacement of the emergency exit ladder shaft at the south western end of the building with a flight of stairs. The Royal Observer Corps was stood down on 30th September 1991 following the end of the Cold War in 1990 with the signing of a non-aggression agreement between Warsaw Pact and NATO countries. The headquarters building was finally abandoned, with nearly all of its equipment still in place, on 31st March 1992. The headquarters building is on three levels built into rising ground, facing south west, of reinforced concrete with internal dividing walls in concrete block work. Most of its structure is protected with an outer brick shell and three layers of asphalt with a minimum 0.9m thick earth covering. The entrance block, approached by an external flight of stairs, stands clear of this earth covering at the north western end of the building. It has extra thick reinforced concrete walls and was originally painted white to reduce heat absorption, but was painted green in the 1980s. This entrance block measures nearly 13m by 7m and contains an airlock and a decontamination room designed to prevent radioactive fallout from being brought into the rest of the building by people entering after a nuclear strike. It also contains a radiator room for the emergency electricity generators sited on the floor below and a filter chamber to remove radioactive particles from air drawn in by the air conditioning system. All these rooms retain original equipment, including signage, which is also included in the monument. To the rear there is an internal staircase which descends to the main floor below. This measures just over 13m by 26m orientated north west to south east with its floor level around 2m below the original ground surface, about 4m below the surface of the earth covering. The main floor is based on an axial corridor. On the north east side there are toilets and showers with the chamber for the sewerage ejector pit to the rear, all retaining the original equipment, fixtures and fittings. Next is the eight bunk bedded male dormitory, the twelve bunk bedded female dormitory, and lastly a small room for officers. The rest of the rooms, including the lower floor, all lie on the south western side of the corridor. At the north western end there is the plant room with the generator room to the rear. In the event of a nuclear attack the building would have been sealed, recirculating the air for as long as possible before taking a `gulp' of air from outside through the filters housed on the upper floor. The plant room still retains the duplicated air conditioning units used for this system. The headquarters was connected to the national grid but had its own stand-by diesel powered electricity generator which is still installed in the generator room and is thus also included in the monument. Next along the corridor is a small fully equipped kitchen with a canteen to the rear which doubled as the off-duty recreation room. Next to this is a room which housed the headquarters' telephone exchange equipment that, as it remained the property of British Telecom in 1991, has been removed. Adjacent to this room was a small store and the stairs down to the lowest level, the floor of which was around 5.5m below the original ground surface. This bottom level measures just over 14m by 8m. At the bottom of the stairs to the right, directly below the telephone exchange room is the wireless room which originally contained VHF radio equipment and still retains some switch gear. This room is shielded against electro-magnetic pulse (EMP), the damaging high voltage surge that is induced in electrical equipment by nuclear explosions, by copper earthing straps around the walls that form a Faraday Cage. The heart of the headquarters occupies the south western part of the lower level with a balcony around three sides on the middle level above, assessable from the main corridor. This is the operations room where post plotters, communication staff who were seated on one side of the balcony, took reports from the group's network of up to 35 monitoring posts. By using data from two or more posts the locations and power of nuclear detonations would be calculated by triangulation using a pair of map boards which are sited in an alcove next to the balcony. This was supplemented by the headquarters' own recording equipment, which in addition to that used by the monitoring posts, included an Atomic Weapon Detection Recognition and Estimation of Yields unit (AWDREY) which automatically broadcast an alarm signal when it detected a nuclear explosion up to 150 miles away. York's AWDREY unit still exists and is included in the monument. This data was then passed via staff known as tellers to the plotters on the floor of the operations room below, supplemented by information supplied from neighbouring group headquarters and other sources via an adjacent soundproofed room. This room originally contained teleprinters but was later updated with faster and quieter messaging equipment. The lower part of the operations room retains its full set of situation boards. These included two illuminated maps of northern England etched onto glass and two wider situation maps showing the United Kingdom and Europe respectively. These were used by the plotters to mark the locations of explosions and to track the plumes of radioactive fallout. The operation room also retains the boards used to keep track of the estimated number of casualties, any losses of communication links and the radiation levels recorded by the group's monitoring posts. The protected Group Headquarters building was only staffed when the Royal Observer Corps was on alert. For most of the time an adjacent single storey brick building to the north west was used by the core full time staff of three to organise day to day administration, maintenance of the group's posts and training for the mainly volunteer staff. Next to this office building is a small store for radioactive isotopes and the footings for a timber hut which was used as a cinema for staff training purposes. Although these structures are not included within the area of the monument, they should be regarded as contributors to its setting.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 2 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.