The Emergency Manual Switching System - E.M.S.S.

The Emergency Manual Switching System was designed to provide a skeleton long distance telephone service for Civil Defence, Military and Emergency Services should the normal network be affected by enemy action. The system was closed at the end of the cold war in the early 1990's.

The U.K. Analogue Telephone Network

In the Nineteen Sixties the UK telecoms infrastructure was run by the GPO / Post Office Telephones and very different from today's British Telecom digital networks. There was no competition from operators in the market such as Mercury, Sky, TalkTalk or Virgin, as there is today. Less than a quarter of people had a telephone in their own home. Due to the lack of government investment in the telephone network, there was often a waiting list for a telephone, residential customers may have had to share a line, with no privacy between them. Unbelievably, there were advertisements to discourage calls at certain times of the day and encourage users to keep the calls to a short duration.

Most local calls (classified as within a radius of 20 miles) could be dialled directly. Automatic long distance dialling known as Subscriber Trunk Dialling (STD) was introduced at Bristol in 1958. The national rollout took in the region of 20 years. So by 1962 other than in the main cities, customers wanting a call over 20 miles dialled '100' for the operator who then connected the call.

Major towns had an automatic telephone exchange known as a Group Switching Centre (GSC). This exchange switched customer dialled calls for the local area. Often there would be a co-located Auto-Manual Centre (AMC) housing operator switchboard positions handling long distance calls, directory enquiry and 999 calls for the local area. The EMSS switchboards were located at an AMC to provide switchboard operators to staff it.

During the Nineteen Seventies, home telephones gradually became more common, so by the Eighties the majority of homes had one. By the end of the Seventies, all long distance and most international calls could be dialled directly, without having to go via an operator. Analogue mobile telephones only started to appear in the early Nineties just as the Cold War was ending, but the high price of handsets and calls restricted them to business people.

Predicted Wartime Telephone Network Overload

All telephone networks are very susceptible to overloading caused by a local or national event, this can be anything from bad weather to a radio phone-in. The networks are only designed to cope with average number of calls. With today's modern digital networks, calls can be rerouted to avoid local problems. During the Cold War period the analogue network didn't have this resilience.

It was assumed overloading would occur during the period of build up to war as people tried to call relatives. Damage caused by war action itself would severely disrupt the network. To prevent overloading affecting essential services and the war effort, a system of disconnecting less essential telephones was introduced in the analogue network, which has been carried forward into the digital and mobile networks too. The disconnection facility is known as the Government Telephone Preference Scheme (GTPS).

This may sound harsh but in the sixties and seventies the network often could not cope with normal traffic and engaged tone was very common. In a war situation it was unlikely to cope with the predicted surge of calls, so by invoking the GTPS, the capacity could be reserved for government, military and civil defence lines

At the time of the Electricity Generator workers' industrial dispute in the early 1970's I recall working by battery lights during a power cut to match the correct level of Preference category for emergency lines, compared with the list provided by the AWG. However it was never necessary to use the Preference Scheme in Kettering as our emergency generator never failed.

Post Cold War Telephone Service Restriction

Even as network capacity has increased to present day standards, voting for a reality television shows can easily overwhelm it. In the present day digital network an additional software tool known as call gapping is used to reduce the peaks of calls to voting or other specific number(s). This wouldn't work in an emergency situation where calls are made to friends and family but not one specific number. The GTPS still exists in the landline network and a similar arrangement, the Mobile Telephone Privileged Access Scheme (MTPAS) is in place on the mobile phone network. They may be used if we suffer a terrorist attack or a natural disaster such as flooding or earthquake jeopardises the telephone network.

The EMSS network and switchboards closed in the early nineties at the end of the cold war. The GTPS and post cold war ACCOLC for mobile phones still exist and are likely to continue in one form or another. This should not been seen as anything sinister. In the past it has been necessary to use the GTPS when telecommunication equipment has been accidentally damaged to ensure the emergency services can still function.

Cold War - Government Telephone Preference Scheme

This scheme works by separating telephone lines into three preference category groups (Pref Cat).

The first stage of disconnection prevents Category 3 customers from making calls. The second stage of disconnection prevents both Category 2 & 3 lines from making calls. The Category 1 lines have no disconnection facility. All lines regardless of their category can receive incoming calls. So even with the maximum level of disconnection enabled, a Category 1 line would function normally as they could still make a call to a Category 1, 2 or 3 line.

Within each GPO Telephone area, a small group of employees in the 'Area War Group' (AWG) liaised with government and the military to maintain a list of lines in Pref Cat I & Pref Cat II. When these lists changed, engineers were instructed to take action to modify the customers exchange line in the exchange.

The Trunk Subscriber

A special type of customers line existed in well before the Cold War period and continued until the telephone network became digital. These customer lines terminated directly on the public switchboard and where known as 'Trunk Subs' deriving their name from Trunk Exchange and Subscribers (the old name for customers). Typical customers would usually be the Police, Fire and Ambulance control centre dealing with 999 calls. When someone dialled 999 and asked the GPO operator for the Police, to save the time taken by dialling a number, the operator would plug into the Trunk Sub to the Police control centre. If the Trunk Sub customer picked up their telephone, or plugged into a line on their private switchboard, it would light a calling lamp on the GPO switchboard, and be immediately answered by the operator.

A variety of customers were connected as Trunk Subs, the three blue light services, Military Establishment as well as U.K.W.M.O. Group controls, Local Authority Emergency Centres (LAEC) and Regional Government Headquarters (RGHQ). There were other uses as well, from special phones at exhibitions to the Queen's Train making an overnight stop in a siding.

Customers lines to and from the EMSS are given a rather anonymous Trunk Sub number. This meant that GPO operators never needed to know the identity of the Trunk Sub, as incoming callers would just ask for a Trunk Sub number in a certain town. For example, Mytown Trunk Sub 11 would ask for 'Anytown Trunk Sub 9' The call would pass through the EMSS network from 'Mytown' until the 'Anytown' operator connected the call to its Trunk Sub 9. Neither operator needed to know the identity of the caller or called line.

The Emergency Manual Switching System (EMSS)

EMSS Switchboard Room

EMSS Switchboard Room

The Emergency Manual Switching System (EMSS) consisted of a network of 300 manually operated switchboards that would only be activated in war. It may be used during the transition to war, if normal operator service were suspended. There was an option to handle the EMSS calls on the 'Normal' peacetime switchboard. In the Post-Strike phase the EMSS would operate from a switchboard in the basement of the exchange building, providing service to essential users during the recovery phase

Many essential locations were connected directly to their nearest EMSS switchboard, these include all UKWMO Group Headquarters, Regional Government Headquarters, Council emergency centres (Main and Standby). Each Armed Forces Headquarters (AFHQ) was connected to two different EMSS.

This picture shows the type of plug and cord switchboard used for EMSS. Here at Worcester there are twelve operator positions, each handling up to fourteen calls. In an adjoining rooms, there is the apparatus room, a toilet / washroom, kitchen / restroom and a dormitory room. All rooms have filtered air conditioning. The equipment remains in situ but has the power removed and all circuits ceased. Worcester is larger than most EMSS exchanges as it was an important node in the network, so much so that a separate two cylinder standby diesel generator is fitted. The normal peacetime exchange itself has two large marine diesel engine driven alternators for standby power.

EMSS Structure

EMSS Network

The gallery associated with the left hand side image contains large photographs of a single switchboard position. One section of the incoming and outgoing multiple, view of the apparatus room, the rack containing the relays to light the calling lamps and 6V transformer, one of a number of relaysets terminating the essential user's lines, the Test Jack Frame (TJF) and a closeup showing circuit designations. The final photograph is the small standby generator.

The EMSS call handling network is shown Red in this drawing. The Area War Group (AWG) and Regional War Group (RWG) are Post Office / BT administrators responsible for the network. The Yellow is the normal peacetime network, or what remains of it post strike. Calls could be received and returned to any portions still working.

During the eighties, probably prompted by the privatisation of BT, the company separated its own emergency network from the EMSS network. It had interconnections into Regional Government and Military establishments as well as interconnection with the EMSS network.

EMSS Network Details

Worcester Interconnections

EMSS Network at Worcester

Click Map to Show Circuit Quantities & A886

Circuit Designation

Circuit Labels

The EMSS network comprised of dedicated circuits not used for normal day to day calls, these are known as Emergency Circuits (EC) connecting switchboards together. This portion of the Test Jack Frame on the right shows, the first Gloucester circuit (GR/EX 1 in black) at position 201 is EC113534 on the Red label. These ECs are quite separate from the circuits to and from Gloucester carrying normal phone calls.

Worcester is a major node in the EMSS network. Using the diagram on the left, it can be seen there were connections to minor switchboards across the Midlands. Additionally there are connections to other major nodes in the national network. Some as far away as Truro, Perth and Portadown. Click the link under the map for the list shown number of circuits to each destination.

Calls could be connected across the whole country just using the EMSS network. But in order to connect calls to people and organisations not connected directly to EMSS, circuits were also provided into the normal public network. At Worcester a group of 10 outgoing lines to gave access local area customers and a further 10 outgoing lines for National Number Dialling. A small quantity of Operator Assistance 100, all Priority Answer and all Emergency 999 circuits could be answered in the basement if it was necessary to stop using the normal operator switchboard on the top floor of the building.

In the run up to war the appropriate 'Military' or 'Civilian' ex-directory number would be issued to people or organisations allowed to use the EMSS service, but without directly connected 'Trunk Subs'. Additionally the users would have Category 1 preference on their telephone lines so they could still make calls if service was removed from non essential lines. These ex-directory numbers were given priority (PRT) over normal code 100 operator calls when the 'Normal' switchboard was being used. To signify this, the switchboard calling lamp white Opals were marked with a 'P'. When switched to the EMSS, they had red lamps and orange labelling.

A quick look in the Tk Sub records for Worcester showed those for Police TkSub1, Fire TkSub8 and Ambulance TkSub5, additionally for local government Tk Sub 20; Worcester County Hall (County Emergency Centre) and Tk Sub 32; the RGHQ 9.2 at Drakelow, Kidderminster ( 1141 Code QHKD ).

Central Government Bunker Corsham

Corsham Bunker to E.M.S.S.

EMSS Network to Corsham

De-classification of documents relating to the Central Government's Emergency War Headquarters (CGEWHQ) at Corsham, reveal that in 1968 it had a total of 37 lines to EMSS switchboards around the country. On the map, Corsham is the Red dot and the E.M.S.S. locations are shown in Green. Note the similarity with the more distant sites connected to Worcester in the previous topic. Perhaps these interconnection points changed after '68.

EMSS        Lines  |    EMSS        Lines
Reading     10     |    Carmarthen  2
Worcester   10     |    Exeter      2
Bath         3     |    Lancaster   2
Salisbury    3     |    Perth       2
Taunton      3     |

Comparing the 1968 Corsham map with the Worcester 1992 long distance circuit map, shows a striking similarity, indicating Corsham was interconnected with the major node sites. Some of the differences may be due to changes to node sites during the three intervening decades. (Salisbury - Bournemouth; Carmarthen - Merthyr Tydfil)

Corsham was a very well kept secret despite it having a large switchboard connected to the nine EMSS sites listed above. I had expected it would simply have a Trunk Sub number at each of the interconnecting EMSS's. That could be true, but at Worcester, there didn't appear to be a group of 10 Trunk Subs for those corresponding circuits. However on the face of the switchboard there are a series of 10 outgoing jacks marked as 'PW1151--' and each jack has an individual number. These numbers correspond with the 10 incoming jacks and calling lamps, marked PW115159 to PW115168. See Worcester's Jack field

Could these be the circuits to the CGEWHQ at Corsham? Any feedback on this matter would be appreciated, or could arrange access to any remaining EMSS listed above via the [Contact Me] tab at the top of the page.