COLD WAR EARLY WARNING SYSTEM
By Kevin Sanderson
AN ARTICLE ORIGINALLY PUBLISHED IN
THE THG JOURNAL AUGUST 2003
WARNING THE PUBLIC
From the early sixties until the early nineties at precisely 9 oclock,
the frequency of the tones used to supply the standard GPO time service
TIMs 3 'pips' ('at the third stroke') changed from
its normal 900hz to 2500hz.
This relatively small and normally unnoticed change in the tones was
part of the engineering test and monitoring process of Britains
'semi secret' telephone line based Nuclear Early Warning System.
MANUAL SIREN CONTROL
The system was not military however and its sole purpose was to warn
the general populace (you and me) of impending doom! The government
publication UKMWO stated "As far as the system described in these
pages is concerned, experts have calculated that its contribution could
amount to the saving of as many as six to ten million lives - simply
by warning enough people in time!"
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
In its normal state the A and B wires are connected to earth at the
control point, at the terminal end the A wire is connected to earth
and the B wire to negative 24 volts. The line relay 'C' on the B wire
remains operated and contact C1 holds signaling relay 'B' in an un-operated
state. Relay 'A' at the control point is also operated and this is used
to detect any line faults or power failure of the equipment at the terminal
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' signaling 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.
The photo shows a siren control cabinet still existing at the side
of the road in South London
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
In the early sixties SYSTEM E was phased out and replaced with a carrier
based system (carrier systems use signals not normally audible to the
human ear 'superimposed' over the top of normal speech signals so as
not to interfere with normal conversation or signaling). The early carrier
systems used on 'line' links were known as 'WB' or 'Wire Broadcast'
The System for alerting the 'Carrier Control Points' (the same Police
Stations used by SYSTEM E) of which there were 250 spread across the
country, was known by the code word 'HANDEL' and was cleverly designed
to be sent 'over the top' of the existing network around the country
that was used to distribute the 'TIM' time signal , the reason for this
was two fold, one: the network already existed and would therefore save
time and money and two: it was a monitored network and would therefore
need no separate fault monitoring or reporting should anything go wrong.
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 Control Points were also connected to some 4000 'warning
recipients' (Civil Defence HQs, Hospitals and the public utilities
etc.) and nearly 900 ROC (Royal Observer Corps) underground posts all
of which had 'carrier receivers' in order to receive the broadcast warning.
To continue click here
Last updated 9th January 2005
© 2005 Subterranea Britannica