This topic describes both the United Kingdom Warning and Monitoring Organisation (U.K.W.M.O.) and Regional Government Headquarters (R.G.H.Q.) communications from its inception in the early sixties, through the seventies and early eighties. Both networks collectively known as the Civil Defence network. A Home Office review identified the need for an upgrade which took place during the mid-eighties and replaced the systems described here by 2nd Generation equipment.
1st Generation Speech and Telegraph Networks
Overview of the Networks in the U.K.
The UKWMO network is used for its role in reporting of nuclear detonations and fallout warning. The Government Control Network (GCN) is used by Regional Government Headquarters (RGHQ), or Zone Headquarters (ZHQ) in Scotland to communicate with Local Authority Emergency Centres in their region or zone. Although the UKWMO and GCN networks are separate entities they were joined between the UKWMO Group and the RGHQ or ZHQ.
Both the UKWMO and GCN were of a similar design and interconnected so they can be treated as one, the Civil Defence Network. Both networks used GPO landlines to link between nodes. A single landline carried both speech and telegraph signals, at each node the speech circuit terminates on a telephone switchboard and the telegraph circuit in the message centre. Many of these links had a duplicate standby radio circuit provided by the Home Office, thereby making the link totally independent of the GPO network.
The UKWMO Private Network
Within the UKWMO there were two distinct networks. One linked Royal Observer Corp (ROC) Posts to their UKWMO Group Headquarters for speech only, this is dealt with in topic: Group to Post Communications in the website menu. The other larger network, shown in the diagram above, linked adjacent group headquarters together. This network had two sub-networks one for speech and the other telegraph. Telegraph is for sending hard copy messages between one or more places. At this stage of development, there was only a single landline with a standby VHF radio link between the adjacent groups carrying both speech and telegraph signals. The hilltop masts carrying these VHF links were often the same ones carrying the GCN at but as UHF links.
Although the UKWMO network only connected the adjacent group headquarters, the use of message centres made it possible to send messages between any two locations even though they were not directly connected. The messages could be broadcast to many locations if required.
Of the five UKWMO Sector Headquarters, only Preston and Lincoln Sectors were directly connected as they are adjacent, therefore all other inter-sector traffic had to be relayed via another UKWMO Group. During the late seventies inter-sector traffic had grown to an extent that warranted the installation of two direct landlines between each sector. Unlike the inter-group landlines, these newly provided circuits didn't have a radio standby.
Government Control Network
The Government Control Network (GCN) like the UKWMO network had two sub-networks, one for speech and the other for telegraph. The GCN was centred around the ZHQ or RGHQ, linking it with its adjacent ZHQ or RGHQ, Armed Forces headquarters (AFHQ) and each Local Authority Emergency Centre in the counties assigned to it. A single landline carried both speech and telegraph signals, with standby radio systems. The bridge between the GCN and UKWMO networks was made between the UKWMO Groups and Regional or Zone headquarters serving the same geographical area.
I don't have a diagram to show the GCN network during the first generation time period. Instead here is an extract from a declassified document, the UKCICC(H) Joint Signal Instruction. At this time the document was written the Sub-Regional Headquarters (SRHQ) was the name for the RGHQ.
UKCICC Joint Signal Instruction Part 5
The Government Control Network
119. This network provides the following facilities:
a. A landline and radio link between adjacent SRHQs, both within and
outside individual regions.
b. A landline and radio link from the SRHQ to each county wartime
headquarters (both main and standby) within the sub region. In the case
of Greater London, the SRHQ will be linked by line and radio to the
headquarters of the 5 London groups and, in addition, each group will have
a "speech only" radio link to an alternative SRHQ.
c. A tape relay centre at each SRHQ, providing duplex (two-way) teleprinter
facilities to adjacent SRHQs and to county wartime headquarters (both main
d. A landline link from each SRHQ to the Emergency Manual Switching Scheme
e. A landline and radio link from each SRHQ to a selected Group Headquarters
of the United Kingdom Warning and Monitoring Organisation (UKWMO).
f. A "speech only" radio link from each SRHQ to the headquarters of the
various police forces within the sub region.
g. A landline link between the main wartime headquarters of each county
and an appropriate police headquarters.
h. In the case of metropolitan counties, a landline and radio link
between the main or standby headquarters of the county and the
wartime headquarters of each metropolitan district.
j. In the case of Greater London, a landline and radio link between the
headquarters of each London group and the wartime headquarters of each
London borough within the group.
k. A "speech only" radio link between the headquarters of each London
group and neighbouring London group.
l. A landline link from each county wartime headquarters (both main and
standby) and each London group to the EMSS.
120. Where both landline and radio links are provided, they are complementary,
and terminate on common switchboards. The landline circuits carry simultaneous
teleprinter working, with the radio link providing an alternative circuit if the
landline circuit fails.
121. UHF radios are also provided between SRHQs and the aircraft and helicopters
of the regional air squadron to facilitate the passing of reconnaissance reports.
If the squadron are reinforced by other light civil aircraft, other telecommuni-
cations might have to be improvised.
122. As a further standby measure, in each sub region there will be a reserve
of up to 10 HF radio sets. These are transportable, have easily erected aerials
and are omnidirectional. They have facilities to recharge their batteries or to
operate off standby generators. Their range is about 20-30 miles and consequently
they could be used in the last resort to plug the gaps in the GCN. They will be held
under Home Office control within sub regions.
Note. This document refers to a number of topics covered elsewhere on this website. These topics may be found in the website menu or in Alphabetic Index.
Para 120, The system for simultaneous speech and teleprinter working, is S+DX, there is a brief overview further down this page in the 'Telegraph and Speech over the same Landline' topic. A fuller explanation may be found in the Alphabetic Index / Speech plus Duplex
Para 121, refers to a radio known as AN/ARC 52 a topic within Post Attack Plans / RGHQ Tasks and Communications found in the website menu.
Para 122, is believed to be the SSB125 radio for the Last Ditch Network LDN. Details may be found under Post Attack Plans / LDN Communications in the website menu.
Para 119, sub-paras D & L, the Emergency Manual Switching System EMSS, has a whole topic devoted to it under Post Attack Plans / EMSS Communications in the website menu.
First Generation Telephony
From the sixties until the communications upgrade in the eighties the UKWMO Group, RGHQ and County Council bunkers had manual switchboards with a mixture of public telephone lines and private circuits for use by the extension telephones in the building.
The small Private Manual Branch Exchange (PMBX) shown here has the capacity of 10 exchange lines and 50 extensions, is of the type used at small control centres, such as those operated by County Councils. The PMBX10+50 was commonly used in the public network too. An extension would have to ask the switchboard operator to ring another extension. For outside calls the operator connected the extension to an exchange line and may have dialled the external number too.
The larger multiple position switchboard may have been used in RGHQ bunkers on its own as a manually operated switchboard or in conjunction with an automatic switch. The automatic switches of this era were of the electromechanical type. The operator would connect incoming calls. Extensions could dial other extensions and usually dial an external number by prefixing it with a nine, but some establishments required the switchboard operator to connect the call. Calls to other bunkers over the private networks of landlines and radio links, were usually connected by the operator.
An extension wishing to call another elsewhere in the private network would ask the switchboard operator to connect them. The operator would place the cord into the jack on the switchboard face and operate the 'ring' key. This would call the attention of the distant operator who would ring the distant extension. This could be quite a protracted process as each operator may be dealing with other calls. There may be only one or two lines between switchboards so extensions may have to queue to get connected.
Post Office Emergency Network
During the nineteen sixties and the early seventies, long distance calls over 25 miles, were connected by the public telephone operator. In wartime that service would be compromised so the Post Office set up a small network of special switchboards in protected areas of telephone exchanges to maintain a long distance connection for emergency services. This network was known as the Emergency Manual Switchboard Service (EMSS).
Although automatic dialling of long distance calls became universal by the end of the seventies, the EMSS network was retained throughout the Cold War period as it was assumed the public network would suffer badly in an attack. Before the digitalisation of the UK network in the late eighties, the automatic long distance dialling network provided no alternative routing of calls if part of the network failed. Therefore it was important to retain a manual network which could adapt to a wartime situation.
The EMSS is described in its own topic if you wish to read more. Details may be found under the Post Strike Plans / EMSS Communications in the website menu.
Torn Tape Telegraph Message Centre
The torn tape message switching centre was extensively used in the Civil Defence network, at group headquarters and regional government or zone headquarters prior to the communications upgrade in the mid eighties. Their use wasn't just confined to Civil Defence, but extensively used by the military, as well as large companies too.
Each headquarters had its own message centre. They were connected to a small number of adjacent centres in their own network and a link at each node between the UKWMO Group and its RGHQ. The links could send messages in either direction, and normally worked over the landline, but could be switched to an alternative radio link. Every link had a paper tape reader connected to the 'send' and a paper tape perforator connected to the 'receive'. There were facilities to convert paper tape messages to printed copies and to create paper tapes for outgoing messages from handwritten message forms.
The telegraph network used a 5-bit baudot code sent at 50 baud, which is very slow by today's standards but suited the mechanical devices it was designed for. The five hole code for each character was punched in a row across the width of a paper tape.
This type of paper tape was used by business Telex and for small scale use. For message centres it was desirable to have the message printed down the side of the tape to assist the operators in handling the messages. The small piece of paper punched out of the hole known as a chad is undesirable in a message centre as they create disposal problems and tend to ingress into mechanisms causing faults. To overcome the problems a chadless tape was used which had a square hole cut on three sides but remains attached on the other.
Tape relay centres had cabinets containing three printing perforators like the one below. The tape emerges from one of three holes and collects in the bin below. When the message is finished the tape hangs from the front of the soundproof door ready to be torn off by the centre operators. On the table next to the cabinet containing the printing perforators, is a triple tape reader, used to send messages back to the three distant ends.
At the top of the cabinet are three sets of supervisory lamps and control switches, one set for each tape perforator. As there is no message store in this system it was essential for the operator to ensure there was sufficient paper tape. A supervisory alarm is raised when the paper is low. The circuit has to be blocked to the distant end when the paper or print ribbon was changed.
This section describes in general terms the function of a torn tape message centre as used in Civil Defence in the United Kingdom.
It is very important that message centres in a large network have a series of rules for handling messages. One obvious rule is if you don't have a direct link to the recipient, then specify which link to use, this is known as a routing table. Further rules are needed to cover the case when the desired link is faulty or destroyed by enemy action.
Special care has to be taken with messages intended to be broadcast to all recipients. Simply sending an incoming message to all outgoing links as well as printing it locally would not work. Messages would be duplicated and the sender would get their own message back. A single broadcast message would be like a snowball rolling down a hill and gaining size and crash the network.
Sending a Message
A typist prepares a message, either by typing on a special punch producing a paper tape, or a teleprinter with a tape perforator. The message starts with a header indicating the recipients of the message, the message itself and a run out of blank paper tape. This is torn from the perforator and carried to the tape reader on the link dictated by the routing rules. If the reader is already sending a message the tape is placed in a queuing system which might simply be a clip on the wall. When the tape has been sent, the centre operating staff check whether the message is a broadcast or has multiple recipients, in which case it is transferred to the appropriate reader and sent again to that destination.
Once a tape is placed in the reader, the start button is pressed to begin sending teleprinter signals to the distant end. If that is another message centre the associated incoming tape perforator reproduces a copy of the sent message tape. The distant end might be an end user with a teleprinter and not a message centre, in which case a printed copy of the message is produced. Typical end users of UKWMO messages are the Local Authority Emergency Centres.
Receiving a message
An alarm lamp illuminates to indicate the arrival of an incoming message. The centre operator tares the tape from the perforator and resets the alarm. If on visually inspecting the header it is for a local recipient the tape is transferred to a tape reader associated with one of the local teleprinters. The message is printed on the paper roll then torn from the machine and placed in the out-tray to be taken to the recipient.
Indirect and through messages
On receipt of an incoming message, the visual inspection of the header reveals the message is not for here but another recipient the tape must be retransmitted onward. The routing rules determine which outgoing link to another message centre is selected when the message is forwarded. It might be necessary to transit via a number of message centres to find the intended recipient.
Flexibility and Economy
A torn tape message centre was a very efficient way to achieve full message routing throughout a network of locations without having to connect every one to the others. It is very flexible too as the operators can use their intelligence to work around a fault or non functioning centre.
When the UKWMO telegraph network was introduced in 1968 it was piggy backed on the existing speech network using Speech plus Duplex technology ( S+DX ). A fully interconnected network connecting the 25 Group Headquarters in the UK would have required 300 links even though many links between remote points may never have carried a message. The actual network had 53 links, this economy of scale was possible as only adjacent headquarters were connected together, reducing the cost to a sixth, but it still enabled a message to be sent from any point to another via one or more tandem relay points.
Teleprinters for the 1st Generation Telegraph Network
A teleprinter of the cold war era was a large electro-mechanical device resembling an electric typewriter. There was a large public network of TELEX machines in the UK, which due to the high cost was almost exclusively for business use. The TELEX network was dial up, in a similar way to the telephone network, but the two networks were not connected. Some large companies had their own independent network which usually used Post Office leased private circuits. The Post Office Telegrams division had its own 'TASS' private network up until the seventies, for sending public telegrams. This used Creed 47 machines, designated as British Post Office No.11, these printed on a thin strip of gummed paper that was stuck to the telegram document.
Before the FAX machine became popular with businesses during the late eighties, teleprinters were favoured as an 'instant' communications medium as they produced a hard copy. The data rate which was considered fast at the time, was only 50 baud, with a 5-bit code plus 2.5 start and stop bits. The signalling was by sending 80 Volts Positive and Negative along the two wires. A good typist could type faster than the machine could send the characters, to prevent this happening the keyboard was mechanically locked stopping a second key from being pressed, until the previous character had been sent.
Teleprinter No. 7
The Creed 7B was used on both point to point links and terminal points on the home defence network. It has no paper tape facilities making it unsuitable for message centres. The mains power unit, a large box normally sited under the desk provides the 80 volts DC signalling. The motor has an integral speed governor. This makes the Creed 7 series teleprinter less reliant on good quality mains power and in a war situation suitable for use with a standby generator.
The No.7 designed in 1931 is ingenious consisting of hundreds of moving parts. This was the mechanical equivalent of the UART found in computer modems and decoded the 5-bit code and printed the character on the paper. Only capital letters, numbers and a limited number of special symbols were available.
An improved version of the No.7 the 7E, used a different clutch arrangement, this overcame the problem where the 7B printed one character behind the one being received. In the photograph this version of the 7E is designated the 7ERP as it includes a tape re-perforator (RP). The electric drive motor and speed governor (the black a white round box) which powered both the printing mechanism and keyboard can be seen at the front left.
The 7ERP with a separate tape reader can be deployed in a small message centre with a few circuits. Like the 7B it isn't too reliant on a steady mains supply.
The Creed 444 introduced in 1966 and designated the British Post Office No.15 replaced the old noisy No.7 printers for business use. The new machines had two colour printing, a built in paper tape perforator and reader. They were much easier to use as they had an improved keyboard and could store keystrokes. Later on, computer screen based devices were introduced, but the No.15 gave good service until the closure of the TELEX network.
Although the Teleprinter No.15 became well established in the TELEX network during the seventies I have little evidence it was adopted for the Civil Defence networks before the introduction of the electronic message switch (MSX). The reliance on a good mains supply to drive the synchronous motor made the No.15 unsuitable for use with standby generators. However it often appears in secret bunker museums, presumably because they were scrap items donated by BT, rather than being historically correct.
Telegraph and Speech over the same Landline / Radio Circuit
At this time, the rental of landlines was very expensive, so to avoid having two separate landlines for Speech and Telegraph a very clever system known as Speech plus Duplex Teleprinter, S+D or S+DX was used in the U.K. Civil Defence network to carry duplex teleprinter signals over the same wires as duplex verbal communication. This system was not exclusive to Civil Defence, but was used in the public network too.
This drawing shows the principle of the arrangement. At each end of the Private Circuit (Landline) a box of electronics combines the inter-switchboard speech line with a bothway link to a teleprinter or torn tape message centre. A more detailed explanation is given in the topic S+DX listed in the Contents page of the website menu..
In both networks, the S+DX could be switched to the radio circuit should the common landline fail. A special jack panel was provided to switch from landline to radio. During weekend ROC exercises, a test of switching to radio standby circuits was usually undertaken for about an hour.
Radio Backup to Landlines : First Generation
Within both the UKWMO and RGHQ networks radio systems were provided to act as a standby for the landline network.
The UKWMO network utilised single channel radio links in the VHF band. The more extensive RGHQ network radio links operated on UHF with both single channel per carrier and multiplexed links. The Civil Defence radio links used hilltop wireless stations, equipped with standby generators, already used for Police and Fire Brigade radio schemes. All these users are Home Office departments so it made sense using the same hilltop sites. The radio equipment was supplied and maintained by the Home Office Directorate of Telecommunications (D-o-T)
In the period from the sixties to mid-eighties the frequency bands were 147.000 - 147.300 MHz paired with 155.000 - 155.300 MHz which were a sub band of the larger 146 - 148 MHz and 154 - 156 MHz frequency assignment for Emergency Service use. An exclusive Civil Defence band 168.325 - 168.800 MHz paired with 174.025 - 174.500MHz was used exclusively for the UKWMO in accordance with notes N27 N29 in UK Table of Radio Frequency Allocations 1985, ISBN 0-11-513819-6
VHF radio links were provided to supplement the landlines. These provided a duplicate speech circuit between switchboards and additionally the telegraph S+DX could be switched over to use this reserve radio path should the landline fail.
The range of a single VHF radio link is limited to 30-40 miles, so a number of tandem links were required to connect the long distances between group controls. The Belfast to Preston link contains an exceptional hop across the Irish Sea from Slieve Croob to Cefn Du of approximately 118 miles, this only being possible with the use of a power amplifier and phased yagis, over an unobstructed sea path.
At the Group HQ bunker, a windup mast carries a number of VHF 3 or 6 element yagi aerials, pointing at the nearby Home Office D-o-T hilltop sites. Links on less physically obstructed routes might be mounted directly on the building's roof. The chain of hilltop sites use 6 element Yagi aerials on the links, a single aerial is used for both the transmitter and receiver. Some hilltop sites had more than one link between group headquarters passing through them.
The aerials are either mounted with their elements (rods) in a horizontal or vertical direction. Aerials at each end of the link will have the same element polarisation. An aerial of the opposite polarisation only receives a weak signal. This can be exploited to allow the same radio frequency to be reused in the order of fifty miles away if the element polarisation is different.
This arrangement at Coventry is typical of a group headquarter setup during this era. It has VHF radio standby links to seven other groups. The image gallery contains a larger version of this image marked with route, frequency and hilltop information and a route map. As well as the VHF yagis for the inter-group links and master post radio hilltop repeater link, there are two UHF yagis linking it to the two RGHQs in its area.
The enlarged map shows all the individual radio links emanating from Wrexham, Shrewsbury, Coventry, Bedford, Lincoln and Norwich. And a partial set of information for the others. Where the routing of a radio circuit isn't known it is shown as a squiggly grey line. Appealing to ex-DTels staff - If you know the routing for any missing home defence radio links just a small part would be most helpful in building a bigger picture.
It has been suggested that not all the inter group radio links actually worked and some worked but had not been formally commissioned. All the VHF links were switched off as part of the W.A.R.C. project which changed the emergency service radio frequencies during the mid to late eighties. The old UKWMO VHF link frequencies in the 147 and 155 bands were reallocated to the emergency services when they migrated from 100 MHz, and the circuits migrated to the RN1 and RN2 networks that are described on the topic page for the 2nd generation of communications.
RGHQ Radio Links
In this first period the bands used were 452.000 - 452.225 MHz paired with 466.000 - 466.225 MHz and some additional channels in the larger 451 - 453 MHz and 465 - 467 MHz Emergency Services band which was mainly used for Police personal radios. There were two other bands 455.875 - 456.000 MHz and 468.875 - 470.000 MHz exclusively used for RGHQ links.
The shorter wavelength of these UHF bands lends itself to the use of a high gain aerial with many elements. This photograph of a local council control centre shows a 12 element UHF yagi aerial, typical of the type used on RGHQ links to councils and other users.
Compared with a UKWMO Group HQ, there were a large number of circuits radiating out from a typical RGHQ, which dictated a different linking arrangement. If they operated a single channel per carrier like the UKWMO there would be problems due to the large number of individual transmitters, receivers and aerials required at the RGHQ as well as the hilltop sites. A technique known as multiplexing allows a single radio channel to carry seven circuits. One circuit is carried at normal speech frequencies and six are translated to higher frequencies, the resulting combined output is used to modulate the radio transmitter. The radio receiver output is fed into a demultiplexer to separate the individual speech circuits. A pair of multiplexer / demultiplexer equipment is needed at each end of the radio system.
In this link map, the circuits from individual sites to the Thurfield mast are single channel links but the last hop to the RGHQ is a multiplexed link. A more detailed description of analogue speech multiplex process may be found on this website.
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