The ROC Post
Physical Appearance
This photograph is typical of the exterior view of a ROC post. A 20 ft vertical ladder leads to an underground chamber 7ft x 16ft x 7ft high. This houses the observers and their instruments and welfare facilities. Conditions were very primitive, there was no running water, gas or mains electric. The only communication with the outside world was the Tele-Talk device, connected to ROC Group HQ and the Carrier Warning Receiver. No telephone was provided. One has to admire the dedication of people prepared to lock themselves away in these conditions.
Measuring Devices
A Ground Zero Indicator (GZI) shown above, was employed to record the position of a Nuclear detonation. This consisted of 4 pinhole cameras in one enclosure. Special light sensitive paper recorded the position and size of the fireball. This gives the direction bearing from North to the fireball and an elevation reading. Within the post, a Bomb Power Indicator, a pressure detector displays the peak pressure of the blast wave. Its needle stays at the highest pressure recorded until reset by hand.
After a detonation, the direction and elevation of the fireball and size of the pressure wave would be passed to ROC Group HQ using the Tele-Talk unit or Radio. ROC Group HQ would use the direction information from two or more posts to determine the exact point of detonation by using triangulation. Once the position of the detonation had been calculated, Group HQ could estimate the yield (size) of bomb from the pressure wave reading. The height of the centre of the fireball could be determined from the elevation readings. A detonation at ground level (ground burst) would create fallout. Whereas a similar bomb exploding so its fireball did not touch the ground (air burst) would create little fallout. |
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Using a Geiger counter head, pushed up a tube from safety of the underground room, the observer would monitor radiation levels. Regular readings of the radiation from the subsequent fallout from a bomb would allow the ROC Group HQ to plot the progress and path of the fallout plume. The geographic area controlled by the Group HQ was sub-divided into Warning Areas. Fallout warnings for affected areas would be issued via the ROC Group HQ landline connection to the Carrier Control Points. As fallout does not respect arbitrary ROC boundaries, ROC Group HQ's would liase by passing on readings to their neighbours.
Selected posts had equipment to allow them to make meteorological reports for ROC Group HQ. This would help forecast the fallout path and its arrival at any location.
A Typical Post Cluster
Posts were typically grouped together in threes or sometimes four, to form a cluster. Grouping the posts in a cluster allowed the location of a nuclear detonation to be calculated with more accuracy. Each post was numbered within the Group area. One post in the cluster was designated as the master post, its number would end with a 0 or 5. The other posts within the group followed sequentially, resulting in a numbering scheme like this, the master post is listed first;
10 11 12,
15 16 17,
20 21 22 ...
ROC Post Communications
Warning Receiver
All ROC Posts were equipped with a Carrier Receiver so they could be alerted of an impending attack. Posts that were warning points, had a hand operated siren to alert the local people when they received the spoken message over the receiver.
Teletalk
To communicate between posts within the cluster and from post to Group HQ, a Tele-Talk device was used. The orginal AD3460 Teletalk was battery operated requiring 6 volt and 67.5 volt batteries. Modernisation introduced the Loudspeaking Telephone AD8010. Like the WB1400 it is line powered.
When switched on the Teletalk would be in listen mode on the private circuit. If the Group HQ operator spoke; this would be heard at all the posts in the cluster. To speak back, a switch was depressed, and the observer spoke towards the loud speaker grill, the other posts in the cluster would hear the reply. The posts in the cluster could talk amongst themselves. The arrangement is very similar to an Intercom.
 AD3460 Photo - Courtesy of the Skelmorlie ROC Post Museum |
<<<<Before |
 AD8010 |
Group HQ would not be continually monitoring every cluster's private circuit, so to attract the attention of the operator, another key on the AD3460 Tele-Talk applied a 67.5 volt battery between the line and earth. Causing a relay to operate a lamp on the operators position.
In the diagram above, it can be seen that all three ROC posts (marked in Blue) shared part of the private circuit back to the Group HQ. At telephone exchange B, a branching panel was used to join all four parts of the private circuit. This allowed all three posts to speak to one another and also to Group HQ.
The position of ground zero for the bomb (marked as a Red dot) and the subsequent radiation due to the fallout in the grey area would be relayed back to Group HQ.
Telephone
Contrary to some belief there was not a telephone in a ROC Post, the only means of two way communication was via the Tele-Talk or in the case of a master post, radio. Posts had no contact with the local police station via landline or radio.Would it work?
The weakest link in the Tele-Talk private circuits to the Group appeared to be the long pole routes carrying the overhead wires to the post. The same wires connected the Warning Receiver and the Tele-Talk unit to the local telephone exchange so both would fail together. Telephone engineers regarded these as a bit of a joke. In the film Hole in the Ground, the featured post sent an observer out in the fallout to clear the line faults caused by the bomb exploding. This was not an easy task in peacetime yet alone a post nuclear holocaust.
The circuit from the post to the nearest telephone exchange was a dedicated set of wires. The remaining part of the circuit back to Group HQ normally consisted of one or more switched lines. In peacetime these carried normal telephone calls between exchanges. For Royal Observer Corp exercises, these circuits were switched over for ROC use. Each circuit had a designation consisting of EC and four or five digits (EC1234) "EC" meant Emergency Circuit. Readers employed by the GPO as switchboard operators may recall being involved with the switching of the EC's as they were known.
As part of the improvements made during the 1980's many of the overhead wires were put underground. Dedicated rather than switched circuits were used for the Post / Group HQ link. The Carrier Receivers and Tele-Talk units were modernised.
Radio Communications
From 1972 onwards, the master post of the cluster was equipped with a single channel VHF radio, allowing it to contact the Group HQ. Dual frequency simplex operation was used, so posts could not communicate with each other. Adjacent Groups worked on different frequencies, so posts would be isolated if their Group HQ was knocked out. When the radio scheme was replaced in the 1980's, posts had 3 channel single frequency simplex radios, these would allow posts to talk to one another and to other Group HQ's