The ROC Group HQ

Function

Each Group HQ had twenty to thirty ROC posts within its control. Each collecting data and forwarding to Group for processing. Bomb detonation locations and estimated yield were calculated. Radiation readings were used to plot the path of fallout. Each Group HQ area was subdivided into Warning Districts. If fallout was imminent in a District the "Fallout Warning BLACK" would be issued via the Carrier Control Point (CCP) for the affected district(s). Eventually the "Attack Message White" or All clear would be issued via the CCP when fallout levels had dropped to a safe level.

A former ROC Warning Officer has kindly supplied this site with his personal recollections of his role. Please see the page navigator at the bottom of this screen.

Sector and Group Locations

Under the United Kingdom Warning and Monitoring Organisation (UKWMO), there were Twentyfive Royal Observer Corp (ROC) Group Headquarter serving the UK, five of these (shown bold) acted as Sector Headquarters too. Preston also had the facility to issue the HANDEL attack warning message to the carrier control points as explained on another topic page. The locations were not a secret. Almost all were listed in their local telephone directory under "Royal Observer Corp" quoting an address and phone number.

Triangulation

Posts collected information of bomb detonations with their Ground Zero (GZ) camera, this gave a bearing to the fireball. The Group could use two or more of these bearing to work out exactly where the bomb had detonated. This was performed by triangulation. The point under the bomb was known as Ground Zero. A term that has become well used since September the Eleventh 2001.

Triangulation uses a map of the area with known points marked on it, in this case the ROC posts. (A, B & C in the diagram to the left) Measuring the bearing angle from North as a reference, lines from each location are drawn. The detonation occurred where the lines meet (marked GZ in Red). Only two posts needed to have witnessed the fireball for a Ground Zero location to be determined. In the 21st Century this may seem primitive, however it was very effective. The UKWMO was set up more than 10 years before pocket calculators came onto the market. A pencil was not affected by EMP and did not require batteries.

Burst Height

Once the ground zero had been triangulated, the height of the detonation could be calculated using the GZ Camera's elevation data. Nuclear bombs may have been detonated at different heights to suit the target. If this is above ground it is known as an air burst. Data regarding the detonation height is important in predicting fallout. The height affects the amount of fallout created by the bomb.

Fallout Plotting

Using the radiation readings supplied by the ROC posts, the known wind direction and speed, enabled the fallout to be plotted. This would be updated as each set of readings was received. A plastic panel overlaid with a map was used to display the track. A soft wax pencil, which could be wiped off, was used on the rear of the panel. Just above the plotters hand is the bomb GZ, a red mushroom. The Horsham warning district boundaries can be seen in the area below her sleeve. The small numbered dots are the posts. The sloping lines near the bomb marker are the Group HQ boundaries. Colchester COL to the left as we view the photo. Maidstone MAI is below Colchester. The bottom of Bedford is just above the bomb marker.

Communications

Communications with the ROC posts by Tele-Talk and radio has been mentioned in the "ROC Posts" Topic. At the Group HQ, the Tele-Talk lines from the posts connected with the Post Display Plotters located on the balcony. If a post operated the "Call Group" button a lamp glowed to attract the plotter's attention. The numbers on the white boards are the post numbers, the master post for each cluster heads the column. Master post numbers increment by five starting from ten.

Communicating detonation and fallout levels is a central function of the ROC Group HQ. In order to perform this role, a network of landline private circuits and radio links radiated out from each group. These are described in more detail in the next topic.