COLD WAR EARLY WARNING SYSTEM

 AN ARTICLE ORIGINALLY PUBLISHED IN 

THE THG JOURNAL AUGUST 2003

Whilst the system and its workings are no longer "secret" – (the entire system was dismantled in 1992 at the "end" of the Cold War) – I do not intend to cover any political aspect but merely try to explain its workings and hence its part in our telecommunications heritage .

The System consisted of two distinct parts, that which communicated the attack warning from RAF Strike Command to the control points (Police Stations) and that which passed the warning to the thousands of warning points across the country.

Following World War 2, the early basic system was known as SYSTEM E. It used DC signaling along private wires from control points (normally Police Stations) to the terminal Points (Sirens) .

Each control point housed a Home Office supplied device the "Autowailer" this was a motor driven device used to supply the timing of the 3 main signals "Air Raid" "Raiders passed – all clear" and "stop" The GPO lines were solely used to communicate these signals to the Siren equipment.

In its operated state the earth on the A and B wires at the control point are replaced with positive 24 volts and negative 24 volts respectively, this releases the "A" and "C" relays operates the "B" signalling relay at the terminal end a contact of which is then used to switch the 3 phase mains supply to the siren. Wherever possible the equipment at the terminal end was located inside a building, normally with the siren on the roof , however in some locations a "street cabinet" was used , painted green similar to GPO cabinets but looking more like "power" cabinets they were 4 ½ feet high by 5 feet wide and 1 foot deep.

Within the cabinet can be seen various items, top left is the siren control panel, top right is the GPO equipment and at the bottom of the cabinet is the main power equipment and switchgear a mains powered heater was also installed. Above the siren controls can be seen a retro fitted "WB1400 receiver" ( a WB600 would have been mounted here until the early eighties) as this cabinet remained in use right up until 1992! (more details later). The Cabinet has now been removed/demolished

The System was then effectively split into two the latter part of the system connecting the carrier control points to the some 18,000 warning points over "normal" subscribers lines using the same philosophy of fault reporting as above – i.e. the customer would report any faults on their line, therefore negating the need for any monitoring system (unless they worked for the GPO the unsuspecting subscriber had no inkling their line was connected to such a system).

The carrier system was sub divided into two separate but mutual systems, WB600 was used to control the Air Raid sirens and WB400 was the means by which speech and warning signals (tones) were sent to the various carrier receivers at warning points. The system used a 72Khz carrier, permanently sent down the line, this was then modulated with an AM (amplitude modulated) speech and signal tones, for reception and demodulation at the carrier receiver. The same carrier could also be modulated with two tones (G and S) to control the switching of the sirens. The most familiar part of the system, at the carrier control point (Police Station) was the unit with 3 handsets known as the "Operating unit WB401A" the two grey "700" type handsets were connected to the duplicated link to the "TIM" distribution system, the link was duplicated for back up reasons, and were known as the "X" and "Y" paths. The black Bakelite handset was connected to the nearest ROC group headquarters for onward distribution of "fallout warnings" to warning points. Picking up either of the "700" type handsets in a "non war" situation would have resulted in the normal "TIM" time signal being heard

An attack warning from RAF Strike Command would be preceded by two tones (P -2400hz and Q - 2600hz ) which signaled the WB401A to receive a message by sounding an alarm on the unit. The "war" officer at the Police station would then lift one of the "X" and "Y" path handsets (either one would do) to receive a spoken attack warning, the system had no facility to "talk back" to RAF Strike Command .

Mounted below the WB 401A was an "Operating Unit 400A" – normally on a table – this was the method by which the officer passed on the warning of attack/fallout to the warning point carrier receivers, there was no direct link between RAF Strike command and the "public" side of the system, all messages being relayed via the Police Control Points. The ROC posts however had direct links to their respective Group controls on dedicated Emergency Circuit Private wires but this was an entirely different network..

The War Officer upon receiving the message from RAF Strike Command would operate one of three switches on the WB400A "Warning" "Speak" and "Call", Warning and Call sent a series of pulsed tones to the warning points which were received on the "Carrier Receiver 400 A" to alert the warning officers, then operating the Speak key allowed the spoken warning to be re broadcast to the now alerted Warning Officers. Warning Officers would then pass on the respective warnings using hand sirens and maroons (sometimes even whistles and rattles) to the general public.

the speech link to the WB400 carrier receivers at warning points. Both the above items were mounted in heavy grey steel cabinets 6 feet high by 2 feet wide. The 72Khz carrier was also generated here. At the remote siren location was a "Receiver Carrier WB600" a picture of which is shown RIGHT

The line from the Police Station was again connected ( via the local exchange) to the remote siren site using an unsuspecting "normal" subscribers line into a standard GPO street cabinet nearest the siren, a filter WB600 then split the line, between the customers line to their premises and the line feeding the siren control unit.

   NEXT PAGE .....

FOR AN ALBUM OF RELATED 

PHOTOGRAPHS-CLICK HERE 

                                               MANUAL SIREN CONTROL

                                                     SYSTEM E DIAGRAM 

               SIREN STREET CABINET

                                   RECEIVER CARRIER WB400 A

                                              WB 600A   RECIEVER