War Resilient Communications

This page documents the Cold War infrastructure of the UK state telecommunications operator, the G.P.O. a Government Ministry in the fifties, that became a nationalised industry, P.O. Telephones in the late sixties. Then privatised in the eighties as British Telecom.

The Need for a Resilient Communications Network

With WWII accord behind us, the fifties saw tensions increasing between East and West in the Cold War, the GPO made a multi-prong approach to improving the resilience of communications in the UK. At the same time there was a large growth in the use of the telephone and many military projects requiring telecommunications services.
Modernisation of the network was underway in the fifties, replacing manual operator switchboards with automatic Strowger type telephone exchanges, to handle long distance telephone calls. This project known as 'Trunk Mechanisation' was also design to move the switching away from London into provincial 'Zone' centres.
City centres were vulnerable to bombing, three deep level exchanges were built in Birmingham, London and Manchester able to withstand a Hiroshima size nuclear weapon. These and other cities such as Bristol had what was called 'Ring' schemes, diverting long distance telephone cables away from the centre and around the outskirts of the city. Some of these rings had specially hardened semi-underground repeater stations, but hardly enough were built to be effective, before the policy changed.
Another proposal was to provide a 'Backbone' microwave radio network as a backup to long distance cables. Specially hardened radio equipment rooms were to be built at these backbone sites. In the event, the demand for long distance television circuits took precedence, so it was many years later before it was implemented, but without the originally planned hardened buildings.

Change of Plans

The Soviet Union surprised the Western Allies by testing a Hydrogen Bomb on November 22, 1955 with a yield of about 1.6 Megatons, about 80 times more powerful than the Hiroshima bomb. This required a major rethink of policy towards hardened and underground buildings, resulting in Manchester being the last underground exchange and no further hardened repeater stations.
Cabinet Office File CAB134/2135 in the National Archives at Kew, dated 26th August 1958, states that the Post Office plans were based on the 1955 Strath Committee Report. This assumed that the U.K. would be faced with an attack by Nuclear Weapons on 10-15 major centres of population.
CAB134/2135 goes on to say that later information, presented in document C.D.(58)2 states it must be assumed this country would be faced with attack on 40-50 bomber and rocket bases as first priority targets, but that, in addition some centres of population would remain as secondary targets. . . .
It draws the conclusion With more than 40-50 targets for nuclear weapons, some of which will change from time to time and all will be subject to the inaccuracy of bomb or rocket, no part of the country could be regarded as safe. While some parts of the country are safer than others, it would seem to be essential not to put a high proportion of our eggs in one heavily protected and expensive basket - the Backbone system - particularly as parts of that system are only 10 miles from probable targets.
The document goes on to suggest 4 principles by which the plans should be modified.
(1) A start should be made at providing some fallout protection at key centres.
(2) Expensive precautions against damage on any route should be dropped.
(3) Vital circuits should be given alternative routes as widely dispersed geographically as possible.
(4) For financial reasons as much use as possible should be made of existing and projected civil radio stations and cable routes.

Chronology of Work

Annual Reports made by the GPO Engineer in Chief (E-i-C) shed light on the developments of the network and resilience schemes, but often lack the detail to be certain as to what they are referring to. The blue italic text from these annual reports are sourced from the BT Archives.

E-i-C Report 50-51

Page 56: Two standard buildings of a specialized character have been designed to give a high degree of protection to equipment housed therein from blast and external fire hazard. They will have gross superficial floor areas of approximately 19,000 and 22,000 sq. ft. The buildings, which are known as Types PR1 and PR2, differ only in the length of the apparatus rooms; they are semi buried and of windowless monolithic reinforced concrete construction. The report goes on to describe features of the air conditioning.

E-i-C Report 51-52

Page 62: Although some interior details of the PR1 and PR2 buildings, described in the last Report (page 56), have yet to be finally settled, the building of a number of each type has started. Plate 7 on Page 108 shows one under construction. . . That photograph and those mentioned in the next annual report are reproduced in the PR1 Construction gallery below.

E-i-C Report 52-53

Page 44: During 1952/53, contracts placed for defence works, including Rotor and Infrastructure, totalled £1.41m. and preponderated over those placed for development of the normal trunk network, which amounted to £1.05m. In addition, instructions were issued to Regions for the installation by direct labour, of audio equipment for 45 Rotor and defence stations and 87 normal works, and for 74 music amplifier installations including nine for the B.B.C. emergency scheme. . . The ROTOR radar project built 31 massive underground bunkers and 6 surface radar stations. Working to 6 Sector operations centres 4 of which were newly built underground bunkers.
Page 45: Contracts have been placed for the initial equipment requirements of the Birmingham and Bristol Provincial Ring Scheme. . . . . . . During 1952/53, contacts were placed for the installation of repeater station power plant to a total estimated value of £325,000. This is less than half the value of plant ordered during 1951/52 (£777,000) because, that year, an abnormal proportion of large plants for the new stations in the Provincial Ring Schemes was ordered.
In this year, the BT Archives contain a number of photographs of the construction of London Kingsway exchange dated 30 January 1952 (TCB417/E17648 to E17671) - See the next topic on this page
Jump to 'Secret Exchanges' topic on this page
Page 67: Almost all the year's work was expended on the provision of buildings for defence schemes, including Rotor.

Seven new R5-type terminal repeater station buildings were completed, one being a Rotor requirement and the other six forming parts of the London and Provincial Ring Schemes.

Twenty-one intermediate carrier station buildings have been completed, all for carrier ring and 24-circuit conversion schemes required for Rotor and defence. Nine of the buildings are of the R4-type with accommodation for a small number of carrier terminals. These are situated at selected points where circuits may need to be extracted to feed Services installations, and terminal equipment is already being provided in one of the stations for this purpose. Eight of the remaining 12 buildings are of the R3-type to house pre-51-type carrier line equipment, and the final four are the first R3 A.C.-type buildings to be provided and will be used for the first route to have 51-type carrier line amplifiers (Edinburgh - Dundee).

Accommodation for Rotor and defence schemes, which was required too urgently to permit the erection of permanent buildings, has been provided in nine wooden huts. Seven of the huts will house transmission equipment, and two will contain power plant. They will serve as temporary repeater stations until permanent buildings can be made available. The huts, known from the manufacturer's name as "Bath" huts, are provided by the Ministry of Works and are constructed in sections 6 feet long and 20 feet wide, with a clear height of 12 feet. As delivered by the manufacturer, the huts are not lined but the contract for erection includes lining with foil-backed plaster board. As the huts would not be strong enough to withstand the lateral stresses imposed if the normal practice of tying transmission equipment racks to angle irons on the walls were adopted, Steel channels 3 in. x 1½ in., set in the concrete base, are erected vertically at intervals along the walls and used to support the horizontal 2 in. x 2 in. angle iron to which the rack tie-bars and cable rack and busbar supports are fixed.
The construction of a number of the PRl and PR2 buildings, referred to in the 1951/52 Report (page 62) has now reached an advanced stage. A building is illustrated in Plate 12, Figs. 2 and 3. The main part of this building is approximately 190 feet long by 50 feet wide and protrudes about 14 feet above ground level. Drying out those large concrete structures, particularly during the wet weather of the past year, has proved to be a bigger problem than had been anticipated. One Region overcame this problem very successfully by using an agricultural grain dryer, and arrangements have been made for other Regions to employ this method where they find it necessary.
Jump to 'Hardened Repeater Stations' topic on this page
. . . . Major building extensions at five terminal repeater stations and extensions of four temporary stations have been completed. . . . . .Much work has been done on the planning and allocation of accommodation in basements of buildings for which special protective measures are to be provided.

E-i-C Report 53-54

Page 17: Special measures have been taken to provide security for trunk communications throughout the country. Schemes have been prepared for giving protection to trunk switching equipment and telephone repeater equipment, and the use of several different cable routes for the groups of trunk circuits between main centres has minimised the general effect of any interruption on individual trunk cables. Note: Trunk = Long Distance
Page 40: Reorganisation of the Control and Reporting System continued throughout the year. Cabling for 25 new stations has been planned and 17 of these are completed; the remainder are proceeding satisfactorily. Rearrangement and provision of a large number of private circuits, in preparation for the opening of these new stations, was put in hand and, for four of the 25 completed. . . . The requirements of an additional 13 stations for a later stage of the Control and Reporting System have been advised by the Air Ministry and preliminary planning has actively pursued. Control and Reporting sounds like part of the ROTOR plan.
Page 52: In connexion with the ring schemes, equipment has been ordered for the diversion of the following carrier cables. Bristol - Salisbury, Patchway - Warmley, Bristol - Oxford, Felton - Warmley, Lyndon - Queslett, Selly Oak - Queslett, Selly Oak - Lyndon, Bristol - Gloucester, Oldham - Swinton, Stockport - Swinton, Oldham - Stockport, Moortown - Rothwell Haigh, Gildersome - Moortown.
Those familiar with hardened repeater stations will recognise Lyndon and Queslett (Birmingham ring), Warmley (Bristol ring,) Swinton and Stockport (Manchester ring), Uddingston (Glasgow ring) and Rothwell Haigh (Leeds ring). On Page 72, there is a report of the completion of 6 PR1 and 1 PR2 type of protected repeater buildings.

E-i-C Report 54-55

Page 13: During the year, the final stages in the present trunk mechanisation plans for London were completed with the opening of London Trunk Kingsway and the incoming section of London Trunk Faraday on 30 October 1954 and 8 January 1955 respectively. Note: Kingsway is the underground exchange. Also during this year, the Speaking Clock rolled out to 34 centres outside the major cities, to play its part 10 years later as the bearer for HANDEL.
Page 40: The first stage of the Control and Reporting System has continued throughout the year and cabling has been completed. Rearrangement and provision of a large number of private wires has resulted in 19 stations being prepared for service. The Air Ministry has opened 17 of these and decided to abandon two. Abandoning these two stations at Calvo and Charmy Down marks the demise of ROTOR plan. Some of the redundant bunkers were reused as Regional Government HQs.
Page 41: At the end of 1954 it became known that the A.A. requirements were totally reorganised, which would mean the cessation of most of the A.A. network. . . . . Instructions to cease some 600 circuits were received. This refers to the stand down of the Anti Aircraft (A.A.) batteries in the Gun Defended Areas (GDA) and the A.A. Operations Rooms (A.A.O.R.). Many AAOR were reused for other purposes, Lansdown -> ROC Sector HQ, Ullenwood -> RGHQ 7.1 and others became Local Authority Emergency Centres, like Mistley, Essex.
Glasgow Ring Scheme Page 54: The Glasgow - Oban coaxial route will terminate at the new Glasgow / Uddingston repeater station, and 24 circuit carrier line amplifier equipment has been ordered for this station to enable the existing Glasgow - Perth - Dundee and Carlisle - Glasgow routes to be be intercepted. This will associate the new Uddingston station with the main carrier network. There is a reference to another new repeater station at Kirkintillock. This was in Washington Rd G66 1DP but appears to have been demolished and replaced by flats, so its not known if it were a protected repeater PR building.
Further down the page: The Margaretting - Tunbridge Wells carrier route will complete a new carrier ring cable system on the South side of London, interconnecting at Guildford with the Northern carrier ring previously provided and at Margaretting with the existing London - Norwich carrier route.

E-i-C Report 55-56

Page 58: Reports that carrier equipment was ordered for a number of routes and these include Anchor - Queslett and Anchor - Lyndon. Anchor being the Birmingham underground exchange, Queslett and Lyndon are two protected repeaters on the Birmingham Ring Scheme.

E-i-C Report 58-59

Page 35: In addition, 24-circuit or 60-circuit line amplifying equipment will be provided for the following cables. The fourth line Woodland - Cheltenham - Shrewsbury (60-circuit carrier cable) Woodland exchange is located at the Central Government War HQ in Corsham quarries.
Page 65: The installation of standby generating plant at the Birmingham Anchor and Manchester Guardian schemes has been completed. Each installation consists of three three-cylinder two stroke oil engines each developing 400 b.h.p. at 600 rev/min and directly coupled to 300 kVa alternators.

Secret Underground Exchanges

Three underground exchanges were built in the nineteen fifties that were classified secret until the mid sixties. These were designed to withstand a Hiroshima type blast but as atomic weapons became more powerful they were rendered useless. The exchanges were used until the early eighties but now only the cable infrastructure remains. To preserve their anonymity during their construction, Birmingham Anchor was known as 'Tunnel Scheme 526' and Manchester Guardian as 'Tunnel Scheme 567'.
The largest was 'London Kingsway' which BT placed for sale in 2008. A good account of London Kingsway following its history from WW2 to present day may be found at website www.subbrit.org.uk
The 'Manchester Guardian' exchange is named after the daily newspaper, although it dropped 'Manchester' from its title in 1959. The exchange came to the public notice on 29 March 2004 when a fire in the cable network severely disrupted the telephone network around the Manchester area.

Birmingham Anchor Exchange

Located below the Birmingham street containing the old assay office whose hallmark symbol is the Anchor. For a time the 'Birmingham Anchor' exchange and cable tunnels had been declared unsafe to work in due to water seepage. But BT refurbished them (circa 2010) to make them safe again as they still carry underground cables across the city.
Birmingham Anchor Exchange (BM/AN) is underneath Telephone House in Newhall Street. The exchange Strowger switching equipment and repeater station were in two large tunnels on two levels, other large tunnels contained the standby generators, fuel tanks and air conditioning plant. All these large tunnels are joined together with smaller diameter tunnels, a detailed layout is amongst the photographs of the excavation and fitting out work, in the image gallery.
As part of the Anchor project a cable tunnel runs South and connects with Midland Exchange, continuing past it, and ending near the corner of Essex St and Bromsgrove St. This point had access from the BT Essex St stores complex, now redeveloped as flats. Before the tunnels became unsafe some of my planning colleagues would walk through them between Midland exchange and Telephone House to avoid getting wet on a rainy day. A Northward cable tunnel was planned to connect to a point at the rear of Hockley Sorting Office, however this apparently was never completed.
A 7 foot diameter cable tunnel, is not part of Anchor but constructed around 1961-62 at the time the City Council were creating the inner ring road, it approaches Aston Exchange and the University but ends outside the 'W i l l i a m   B o o t h   C e n t r e' in Shadwell Street. The other end of this tunnel passing Telephone House finishes at the city end of Broad Street. This is shown on the map in green and connects to Telephone House in Newhall St, which is above Anchor.
Other sources on the web falsely suggest it was possible to walk to Smallbrook and Aston Cross exchanges. A series of deep level cable tunnels do exist around the city but do not give access to those exchanges. Another falsehood on the web, is the assertion the basement of Aston University was connected into the cable tunnels.
A BBC video on YouTube shows plenty of detail in a quick tour of the Anchor tunnel system but wrongly suggests it was the Midlands Regional Seat of Government, but that was actually RGHQ 9.2 located at Drakelow. Nevertheless Anchor was an important place for telecommunications with circuits extending all over the Midlands area.
There are a few visible signs of the Anchor tunnels on the surface. Air vents and lift access points can be seen next to Telephone House in Fleet Street, and also the Lionel Street goods lift access. The Church Street lift is hidden from view at street level, but can be distinguished on the aerial photograph. At the time of the construction of Anchor strowger exchange, above it, Telephone House contained a local telephone exchange known as 'Central', and two trunk exchanges 'Newhall' and 'Colmore Lodge', all using Strowger switching equipment. Anchor's Strowger switches were removed in the early eighties. By 1995 the digital network had completely replaced all Strowger and electronic / transistorised analogue switches throughout the country.
Click to watch the 1998 BBC video of Birmingham Anchor on YouTube
1998 BBC Video
Midlands Today report by John Gregory, first shown on 8th March 1998 and now on YouTube, describing the underground tunnel complex that formed part of the redundant Birmingham Anchor BM/AN telephone exchange built to withstand a nuclear attack in the 1950s. The clip inaccurately describes the exchange as a West Midlands Region Seat of Government bunker, which actually was in the Drakelow Tunnels, Kinver."


Position of Anchor Under Birmingham Streets
Aerial View of Surface Features
Lift Shaft 1 and Vent by Telephone House
Lift Shaft 2 and Vent in Lionel St
Cutting the Tunnels
Tunnel ready for Equipment Installation
10ft 6in Strowger Racks Awaiting Relaysets
FDM Multiplex on 54 Type Transmissions Racks
Plan of entire Anchor Complex
Layout of Equipment Tunnels


Tunneling Work 1954
Tunneling Work 1954
Tunneling Work 1954
Tunneling Work 1954
Tunneling Work 6-March 1954
Bricklaying 1955
Lower floor in Apparatus Tunnel 1955
Upper Floor in Apparatus Tunnel
Empty cable seal around blast door 1956
Incoming cables split to feed MDF
Lead Covered Cables branch to MDF 1957
Lead Covered Telephone Cables 1957
Cable bearers leading to seal and doorway
Vertical Cable Run 1957
Cabling between levels 1957
Bottom of vertical cable run
Sewage Ejectors 1959
Chiller Water Pipes 1959
Plant Room
Air Conditioning Blowers
Ventilation tunnel joining Air Conditioning Tunnel

Hardened Repeater Stations

The connection between the home telephone and the exchange is carried on a single pair of wires. Over the relatively short distances involved, it is economical to bundle these together in large cables, some containing as many as 2000 wires. Over long distances, the use of large cables is not economic. A system of multiplexing 24 analogue speech channels into two pairs of wires was developed. Further developments increased this capacity. By the 1960s a 4MHz co-axial cable could carry 960 channels on two coax tubes, one for each direction of speech. Today 40GB optical fibres have 10,000 times this capacity.
When telephone calls are sent down a long pair of wires between exchanges, the audio signal must be amplified at regular intervals. The amplifying point is called a Telephone Repeater Station (TRS). Most large telephone exchange buildings incorporated a TRS area too. In small exchanges, a special area wasn't warranted for the TRS, in this case the amplifier racks were placed alongside the switching apparatus.
On long distance routes using multiplex equipment, the bulky thermionic valve equipment was housed in a dedicated TRS building, rather than using part of the exchange building. Early coax cables carrying television or multiplexed speech channels required amplifying every couple of miles. Hundreds of TRS were housed in small brick buildings the size of a garden shed. As the amplifiers became transistorised it was possible to house them in special cases in manholes, saving the expense and difficulty of procuring land for a TRS.
Above ground repeater stations were vulnerable to damage in a war, so a decision was made to protect the important routes with specially hardened buildings. At the same time that the three underground exchanges were being built, a small number of hardened repeater stations were constructed to house the repeater equipment. It wasn't long before the policy changed, so just eight of these repeater stations were actually built, six PR1 type and two larger PR2 type.
A two storey semi-sunken hardened repeater station was constructed in 1954 in Sheldon, a suburb on the East side of Birmingham. Known as Lyndon Green (BM/D), it was contemporary with the secret underground exchange, Anchor in Birmingham City centre. At the end of its cold war use, the building served as the Regional repair workshop during the eighties and nineties. In the gallery there are pictures of the property taken in March 2009. The hardened concrete core has brick built offices attached. A similar hardened repeater station was built at Queslett, a Northern suburb of Birmingham, and now houses the 'Beacon (CMBEAC)' telephone exchange.

List of Protected Repeater Buildings

The bracketed letters in the list above are the THQ1141 Engineering Code for the TRS. The Latitude and Longitude numerical values may be copied and pasted into Google Maps or Bing Maps search box.


Portsdown PR1 Underground Floor; Front View
Ground Floor Construction
Ground Floor Construction
Ground Floor Construction
Completed Shell - South View
Completed Shell - Front View of Buildings West Side


Front entrance to Lyndon Repeater Station
East side of Lyndon RS
West side of Lyndon
Aerial View Lyndon RS
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