Landline link to Group
Telephone, Observer AD163
In the early 1960's the original magneto type telephone with a headset and breastplate microphone worn by the observer, "Telephone, Observer AD 163C" used since WW2, was replaced with a loud speaking unit. This device, known as a TeleTalk by the ROC allowed the observer freedom to move around in the bunker and not be constrained by the breastplate cord.
Teletalk Unit AD3460
The TeleTalk or "Units Intercom LB AD 3460" to give its proper description is battery powered, hence LB in its description for Local Battery, utilising the same design of 6 volt dry battery [Battery, Dry No. 27] fitted in the Warning Receiver. Additionally a 67.5 volt battery [Battery, Dry No. 18] is used to send the call signal to the post display plotter. AD3460 is the diagram number, the letters AD designate a series of G.P.O. diagrams for Air Defence equipment.
There is a photograph of the Battery Dry No 18 in the gallery, it is marked as a radio battery, in days before transistor radios, this type of battery would provide the high tension for thermionic valves in a portable radio. This particular battery was manufactured in 1971.
Normally in receive mode any conversation on the cluster's omnibus line may be heard. Before speaking into the loudspeaker which acts as microphone too, a small lever switch on the right hand side of the unit must be pressed downwards. Posts within a cluster can communicate amongst themselves by voice calling. But to attract the attention of the plotter in Group HQ, the lever switch is momentarily pushed upwards to the CALL position and then released.
As posts were usually located on remote hilltops the pair of wires feeding them were often carried on poles along field boundaries making them very vulnerable to blast damage. The same wires fed both the Warning Receiver and the TeleTalk unit so both would be out of action if the line was broken.
Telephone engineers regarded these overhead lines 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.
Landlines within a Cluster
A dedicated pair of wires carried the circuit from the post to the nearest telephone exchange. The remaining part of the circuit back to Group HQ normally consisted of one or more switched lines. In peacetime these carried normal public telephone calls between telephone exchanges. For Royal Observer Corp exercises, or in time of war these circuits were switched over for ROC use. Each circuit was designated with the letters 'EC' meaning 'Emergency Circuit' and four or five digits e.g. 'EC1234'. Switchboard operators employed by the GPO / Post Office Telephones / British Telecom may recall being involved with the switching of the EC's as they were commonly known. On a post's drill night there was no way to communicate with Group HQ as switching only happened for a ROC exercise.
Switching the Emergency Circuits was a complex task when considering that York alone had Forty posts in Twelve separate clusters. This was replicated up and down the country some Twenty Five times. At each staffed switching point, firstly a 'Busy' key stopped the line being used for telephone calls, if a call was in progress on the line to be switched, a small lamp flashed until it completed. When the lamp glowed steadily, coloured pegs were moved from the 'normal' to the 'switched' position. This was fraught with problems as it was very easy to misoperate the switching. At unmanned remote exchanges, the switching clerk in the main exchange had to initiate three calls to two different telephone numbers in a set sequence and time interval.