HANDEL the UK Public Nuclear Attack Warning System
This description of HANDEL should be read as an introduction to the three following pages describing the carrier system WB400 and its successor WB1400.
Development of the Public Warning System
From WW2 until the creation of the United Kingdom Warning and Monitoring Organisation (U.K.W.M.O.) in the early 1960's, Air raid sirens were controlled from local police stations using dedicated private wires (PW). This early control apparatus was designed and maintained by the British Post Office (GPO) and designated "SYSTEM E" by them. This forerunner system is also described on this web site in the topic 'Before HANDEL' should you be interested in the history.
The UKWMO was set up to give public warnings of air attack and fallout from nuclear weapons. The communications system used to convey these warnings to control points in police stations was known by the keyword HANDEL. Police station control points relayed the attack warning, fallout warning and all-clear messages and sirens to the public using radio frequency signals as a carrier for these messages over normal telephone circuits. The carrier had no effect on the operation of the telephone line and the avoidance of private wires (also known a Private Circuits) reduced the cost and improved reliability.
The HANDEL network was installed during the early 1960ís and served until the end of the cold war. Following the Autumn Statement in Parliament on the 12th November 1992, the Home Office announced with immediate effect the United Kingdom Warning and Monitoring Organisation (UKWMO) would no longer function. HANDEL was decommissioned shortly after. Throughout its life the equipment was installed and maintained by what was the GPO, then became Post Office Telephones and finally British Telecom.
The initial HANDEL system had two parts, the WB400 speech broadcast system and the WB600 siren control system. Confusingly both used the same carrier and were actually both integral parts of one system. During the early 1980ís the original equipment was replaced by the new WB1400 system using more modern technology and addressing the shortcomings of the previous one. As it continued to use the same carrier frequency the two could work together during the changeover period. A full description of each system may be found in this section by clicking the Tabs at the top of this page.
National Attack Warning Red
The Air Attack Warning message would originate from a UKWMO warning officer located at a location known variously as Strike Command (SC), Primary War HQ (PWHQ) or Air Defence Operations Centre (ADOC) If that were to become disabled, the messages could be sent from the United Kingdom Warning and Monitoring Organisation (UKWMO) Headquarters in Preston. Using the HANDEL network a verbal 'Attack Warning Red' message would be passed to control points set up in 250 major police stations. These control points would alert the public using the carrier broadcast system.
If nuclear detonations were detected by Royal Observer Corp (ROC) monitoring posts without a national attack warning being given, the UKWMO had processes in place to inform the SC/PWHQ/ADOC to enable them to retrospectively give a national warning. As a backup, the UKWMO groups were instructed to call the carrier control points in their area and issue a local Attack Warning Red.
The HANDEL network utilised the existing GPO / Post Office Telephones / BT Speaking Clock distribution system. If it were necessary to pass a warning message, the speaking clock would be disconnected. To alert the police station Carrier Control Points a short burst of two tones known as P+Q tones preceded the verbal instructions. The P+Q tones triggering an alarm that sounds until the control point handset is lifted.
HANDEL Messages Distributed by the Speaking Clock
The Speaking Clock was first introduced in London in 1936 and was an instant success and the service rapidly spread to all exchanges throughout the U.K. To avoid interruption to this service the Speaking Clock or Time Signal (TIM) as it was also known was distributed on a duplicated rings of lines between major telephones exchanges designed to raise an alarm if a ring failed. The amplifiers at these major exchanges would switch to the other ring circuit should the one currently in use fail, thus maintaining the service.
When HANDEL was first installed in 1962, the Speaking Clock distribution provided a ready made and secure (against breakdown) system of distributing the national warning messages around the country. Branches from the two Speaking Clock rings were taken on two diversely routed pairs of wires to the Police Station's carrier control point.
At the time of the introduction of HANDEL, the speaking clock was sourced from equipment in London and Liverpool with two duplicate clocks at each location. Each clock was a mechanical device based around multi-track magnetic recordings, replaying small sections of the time message all strung together to form a complete message every ten seconds.
In the first generation of HANDEL used with WB400, the warning message prefix P+Q tones were of 2400Hz and 2600Hz. For engineering test purposes, at 08.30 GMT precisely every morning, the usual 1000 Hz pips of the clock were replaced by one of 2500 Hz, chosen to be midway between the P and Q frequencies. Telecomms Instruction E9 E2091 states these special pips should measure -5dBm on a peak program meter to ensure the apparatus functions correctly.
In 1984 the earlier clocks were replaced by electronic units using memory devices to store the message sections. By this time the need to change the pips was removed as the second generation HANDEL equipment for WB1400 now used 1200Hz and 1440Hz for the P+Q tones, which are well within the speech band.
The electronic clocks and analogue distribution network continued to serve the U.K. after the closure of HANDEL in 1992. All remnants of the HANDEL distribution network were removed in 1994 when the analogue speaking clock rings were replaced by digital Recorded Information Distribution Equipment ( RIDE ). These racks of equipment, located in Digital Main Switching Units, were fed with a digital Speaking Clock sourced rings emanating from the B.T. Network Operations Centre near Oswestry.
Fallout Warning and All Clear
If the attack failed to materialise or the raid didn't use nuclear weapons an All Clear message White may be issued at national level from SC/PWHQ/ADOC.
During and following the attack, the network of ROC monitoring posts would report details of bomb detonations and local radiation levels to their UKWMO Group HQ. The network of Group and Sector HQ's would exchange data to create a national picture of detonations and both actual and predicted fallout patterns. As fallout does not respect national boundaries the UKWMO had liaison officers in other European countries to exchange data with them.
The UK was divided into small areas of approximately 100 square miles, known as Warning Districts. Having predicted in which warning districts fallout may settle, the UKWMO Group control would, using their direct line to the HANDEL control panel in the police station control point, ask for a fallout warning to be relayed to the appropriate carrier receiver warning points.
After the attack and when the fallout radiation levels had returned to a safe level, probably after a period of two weeks, the All Clear would be notified by UKWMO Group controls using their direct line to the HANDEL control panel.
Police Station Control Point
The Warning Network
The UK was divided into 250 Carrier Control Points (CCP) located in a major police station. The CCP has duplicate HANDEL handsets to receive the national messages. During peacetime the speaking clock can be heard on these handsets. A third handset connected to the UKWMO ROC Group Headquarters serving the area in which the police station is located. This would be used to receive any Fallout Warning messages and eventually the All Clear. As HANDEL is a two stage system, onward distribution of public warnings required human intervention at the police station to retransmit the message. Neither Strike Command nor the ROC had any direct way of alerting the end user at the warning point. To achieve more granularity, the CCP would issue fallout an all clear warnings to individual warning districts within its area.
|Carrier Control Area||Number |
|Melton Mowbray||071 |
|Market Harborough||078 |
|East Kilbride||309 |
Copper pairs between a telephone exchange and customers premises are able to carry signals well above the range of human speech. This extra bandwidth may be used to carry signals without interfering with the normal telephone operation. Broadband Internet using ADSL is a modern system utilising this extra bandwidth. However other simpler systems known as "Wire Broadcast" (WB) have been around since the 1940ís. A paper read to The Institute of Post Office Electrical Engineers on the 11th April 1949, describes the trial of a multichannel carrier system for broadcasting BBC radio programs over telephone lines.
At the Police Station, the Carrier Control Point (CCP) equipment, uses Wire Broadcast, a 72 kHz radio frequency carrier modulated with speech or tone signals for civil defence purposes. The carrier is distributed via the main telephone exchange, known as the Control Point Exchange (CPE), to all the warning points. Each CCP area is given a number, some of these are shown in the left hand table, the first two digits appear to relate to the telephone area, hence the number range extends beyond the 250 needed if they were numbered consecutively. To provide security against a fault going unnoticed, carrier was distributed throughout the network using existing telephone lines. This helps detect faults in the carrier system and saves the cost of providing extra wires often to remote locations. If the wires become disconnected the telephone would be reported faulty, long before the carrier system was next tested. Filters separated the telephone and carrier signal allowing both to be used simultaneously.
It has been wrongly reported in the past that the 72kHz carrier was broadcast over the Speaking Clock system. Such as - RSGB RadCom July 2001, 'The Voices' Page 35. This myth may be found in the chatter on the uk.rec.subterranea news group too. From the diagram you can see this is clearly not true as the speaking clock only distributed audio voice messages.
The network of GPO / BT circuits comprising the carrier control area were allocated 'Private Wire' (PW) numbers in the series 103xxx where 'xxx' is the carrier area number. For example, Swindon PW/SW 103031, Londonderry PW/NI 103290. The PW number is used for fault reporting and records purposes. In modern terminology a private wire is now known as a 'leased line' or 'private circuit'.
In built up areas mains power operated sirens would be operated by signals sent from the CCP. These were often WW2 siren locations in addition to the receiver they had a control panel to allow local activation. During peacetime the fuses to the siren motor were removed to prevent accidental operation.
First Generation Receiver
Second Generation Speaker
The warning receiver is the part of the system most visible to the general public. The normal telephone line at the premises carried the carrier signal from the telephone exchange to the receiver. In rural areas there were no power operated sirens so receivers were located in premises such as Post Offices, Shops, Pubs, Vicarages or the homes of Police Officers, Council Officials or magistrates, who were deemed "responsible" people trusted to warn the local population by the use of hand sirens, whistles, maroons and gongs. Around 18,000 Warning Points existed nationally.
Additionally a warning receiver was likely to be found on the premises of about 4,000 Warning Recipients who would need to know if it were safe to go outside. These would be Fire Stations, Police Stations, Hospitals, Public Utilities and Feeding stations to name a few.
In the earlier carrier receivers the instructions for the Warning Points were given on a card held in a drawer in the base of the unit. In the later receivers, the instruction card is retained under a clip on the speaker, some police forces issued users with a detailed detailed instruction booklet. Both sets of instructions are reproduced on their relevant pages.