Telecommunications
During my time in Telephone House Belfast I had access to PO / BT telephone cable and duct prints covering the whole of the province. Some of these are restricted and kept under lock and key. When researching a former government or military establishment these prints can reveal some interesting facts. I knew that CSOS Gilnahirk had a telephone link with the network, but what I did not know was how secure that link was until I examined the cable prints for CSOS Gilnahirk in 2004 some twenty six years after the station's closure. To my amazement Gilnahirk was served by three trunk and junction cables. These are cables that normally link telephone exchanges together. The trunk and junction cable would carry high grade circuits etc. Terminating on the Main Distribution Frame (MDF) within the telecoms room at Gilnahirk, there was a cable from Knock, Dundonald and Comber exchanges i.e. coming from three different directions. The Knock cable circuits back to "Oakley" were live but in the event of a failure the circuit could be plugged out and another circuit plugged in from either Dundonald or Comber. The PO Technical Officer on site at Gilnahirk would ring the Technical Officer at Dundonald or Comber exchange and the circuit to "Oakley" was restored in less than a minute. With this level of backup it gives one a true understanding of the importance of the CSOS sites.
To fully understand this importance we must remember that CSOS Gilnahirk was a Listening station and having captured and recorded something of extreme importance from the ether "Oakley" has to be alerted in the same way as a "Flash" signal is passed back to London via the telephone network from any of the UK Stations.
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I came across an odd building at Auldearn near Nairn, it was described on the Historic Environment Record as a radio transmitting station but it seemed to have been a GPO Repeater Station.
Ambaile has a lot of Home Guard files which seem to have come from Caithness Archive. There is a list of high priority GPO sites and this one is the only in the highest priority category - even higher than Inverness Repeater.
It was described as something like being high importance to the ADGB. I can only think that this meant it was linking the radar stations I don't know if they had dedicated circuits or just used the DTN. An ex-GPO friend said there was a similar building near Elgin but I have never found it or any more.