Many of us signed the Official Secrets Act, this protected information for 30 years, so anything pre-1992 is now open. The National Archives in Kew, have files previously classified as Secret, open for public inspection. These form the basis for a number of pages on this website. The Freedom of Information Act, has opened younger files too.

Recent information suggests LDN's replacement RN5 may have had the official name of Home Defence Radio Communications Network (HDRCN) using RACAL or Decca Messenger SSB radios. Any extra information or correction would be helpful. Last Ditch Network

A lot more has been discovered in the National Archives. But this topic needs a little more exploring. Clear photographs of the jack fields on any remaining basement switchboards or a list of their routes would be equally helpful. The incoming jacks usually repeat themselves every four or six appearances, so its not necessary to photograph the whole of the switchboard.

The BTDN (British Telecom Defence Network, formerly the PODN, was funded by the home office until 1993 when it closed. Do you know the locations of the main switching centres. In some places the BTDN circuits shared the EMSS switchboard, but in Chester and Worcester at least, they were in different buildings. Any info would help.

Have you worked on a transistorised 24-ch carrier system, where certain pairs were intercepted and amplified in manholes while the remaining pairs went inside the TRS. Some parts were upgraded with EDL8 Digital MUX and was known as S8S.

GPO / BT people may not recognise this codeword for the network explained in the topic National Communications / All Underground, it may have been known to PO staff as the "Protected Carrier System". I suspect there is more to the network than shown on the map on that page - any ideas?

Do you have colour photos of WB600 receiver external or internal sub boards to replace the B&W photo from BT Archives.

Do you know any ROC Group, Post Radios frequencies, using the ATE Countryman radio, in high-band before the move to 80 MHz frequencies of RN4.

Any pre-RN1 / RN2 era, VHF links for Home Defence / UKWMO, those shown as "Route Unknown" on page Core Communications Network / First Generation, expand the route diagram titled "UKWMO VHF Link Details and Frequencies". I have been supplied with two sets of personal notes / diagrams drawn by DTELs staff used to build this diagram. Do you have anything similar?

Any sketches or lists of links (however small an area covered) of the UHF home defence network between Regional Government HQ's and local authority emergency centres. Era prior to the introduction of RN1, possibly using Plessey valve operated multiplex - ATE800 / 900

Already showing RN1 network diagram but have next to nothing for RN2, so any tiny scrap of information in or around one county or RGHQ would aid understanding immensely. Aerial direction diagrams for masts would be useful too. Do you have any examples of the actual GHz frequencies of RN1 links to determine the channel spacing. Any copies of T.E.I. for the RN1 or RN2 sites?

Still more to find out. Do you know of a location actually issued with the SSB125 radios. We now know the bands involved but not the actual Regional Frequencies used for training? A recently opened PRO file mentions RN5 as a replacement for the SSB125 radios. Did this ever roll out ?

There is a great shortage of information about all UKWMO communications in Scotland so even the smallest scrap would be helpful.

ROC Standard Operation Procedures (SOP) Annex G shows the English / Welsh / NI 80 MHz ROC Post frequencies for RN4, but the Scottish section is marked 'Details not Available'. I am still missing those 80MHz frequencies for Ayr and Edinburgh Groups.

We have none of the five Scottish groups frequencies used prior to the introduction of RN4, at a time when England and Wales were on VHF highband. Did they even have radios in posts before RN4, as we know that Belfast Group didn't.

UHF / Microwave links equivalent to the RN1 and RN2 in England & Wales, are any details of the network available.

I became interested in the UK Civil Defence for the Cold War, as a result of working as a engineer for 'Post Office Telephones' later privatised and renamed 'British Telecom'. Between 1978 and 1981 when I maintained the early warning equipment and visited ROC posts in part of North Northamptonshire and South Leicestershire. At the time I never disclosed this information even to my closest friends. Now more than 30 years have passed since the Cold War ended the Internet provides a good medium to disseminate the details of these defunct systems.

I am always pleased to hear from visitors to the website whether or not you have anything to add to the topics discussed.