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Organisation and methods edit
Great Britain was covered by a number of ROC Groups of which there were 18 in early 1939, expanding to 39 by 1945; the Corps did not operate in Northern Ireland until 1954. Each Group controlled between 30 and 40 observation Posts organised into Clusters of three (very occasionally two or four). Aircraft movements were conveyed from posts to the centre and then as appropriate to the headquarters of Fighter Command at RAF Bentley Priory.
Observation Posts edit
Group Centres edit
Old edit
The headquarters of each ROC Group operated from a control Centre, responsible for and controlled between 30 and 40 observation Posts, each of which would be some 10 km to 20 km from its neighbour. By 1945 there were 39 centres covering Great Britain, controlling in total more than 1,500 posts. (The ROC did not operate in Northern Ireland until 1954).
In order to monitor aircraft, observers used a simple but effective mechanical tracking device. Where the approximate height of an aircraft is known it becomes possible, by using a horizontal bearing and a vertical angle taken from a known point, to calculate the approximate position of that aircraft. Posts were equipped with a mechanical sighting Post Instrument plotter consisting of a sighting system over a map grid. After setting the instrument with the aircraft's approximate height, the observer would align a sighting bar with the aircraft. This bar was mechanically connected to a vertical pointer which would indicate the approximate position of the aircraft on the map grid. Observers would report the map coordinates, height, time, sector clock code and number of aircraft for each sighting to the aircraft Plotters located at the Centre. Positioned around a large table map, plotters would wear headsets to enable a constant communications link to be maintained with their allocated Cluster of posts, usually three in number.
The plotting table consisted of a large map with grid squares and posts being marked. Counters were placed on the map at the reported aircraft's position, each counter indicating the height and number of aircraft, and a colour-coded system was used to indicated the time of observation in 5-minute segments. The table was surrounded by plotters, responsible for communicating with their allocated cluster of posts. Over time the track of aircraft could be traced, with the system of colour-coding enabling the extrapolation of tracks and the removal of time expired (historical) data. From 1942, long-range boards were introduced into centre operations rooms, with Tellers communicating with neighbouring ROC groups in order to handover details of inbound and outbound aircraft tracks as they were plotted on this map.
Specific duties in the centre operations room included those undertaken by:
- Plotters – responsible for updating the plotting table and long range board
- Tellers – responsible for communicating with neighbouring ROC groups, Fighter Command Group and Sector controls, anti-aircraft batteries and searchlight units
- Alarm Controllers – responsible for liaising with the Police, the National Alert System, the Ministry of Home Security and with local industrial facilities
- Interrogator – responsible for liaising with ground controlled interception (GCI) radar units
- Duty Controller – together with an Assistant Duty Controller and Post Controller, responsible for supervising both the centre plotters and group observation posts