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.

Warnings in WW2 through to the Nuclear Age

From WW2 until the establishment of HANDEL the 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 General 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. Siren could also be set off by an on-site control box associated with the siren. Examples can be found in the 'Power Siren' topic.

At this time there was no National Warning system, but instead the local police received notification of enemy bombers in the vicinity and when they had passed. A clue to how the warnings were propagated in WW2 are given in the report of the development of the the new nuclear warning system. The system allows audible warning and verbal information to be passed, simultaneously, to a large number of recipients within an air raid warning district, without the need for Post Office operators to make individual calls to police, fire stations, air raid wardens etc., as was necessary in the last war.

Development of the Public Nuclear Warning System in the UK

I am indebted to Dan Glover, for taking the time to extract the historical information from the G.P.O. E-I-C reports in the B.T. Archives, while researching for his own website.

The G.P.O. Engineer-in-Chief Annual Report for 1950 / 51 Tells of early development work. At the request of another Ministry, a single-channel carrier wire broadcasting system has been developed which could be used to provide a special "broadcast" information service. Equipment has been installed for a pilot experiment and has been used to demonstrate its potentiality as a means of providing simultaneous one-way communication from a few control centres to many receiving points. and goes on to say Contracts have been placed for further single-channel equipment which will enable a full-scale field trial of the system to be made over an area of 400 square miles to subscribers on nearly 50 telephone exchanges. This is some 10 years before the full rollout of HANDEL.

Receiver Carrier WB200A

WB200 Receiver

Extracts from the 1951 report say Intensive development work on the carrier wire broadcast system for use in distributing special information, e.g. civil defence warnings continued (see last report p.44). Under Home Office authority, work was put in hand, in April 1951, to provide experimental apparatus and equipment for a field trial at Bristol. The system allows audible warning and verbal information to be passed, simultaneously, to a large number of recipients within an air raid warning district. . .

Equipment has been installed in the outer area and 350 subscribers have been connected to the system for the purpose of the trials. The apparatus required at the subscriber's installation consists of a carrier receiver, filter unit and standby 6-volt car battery provided to cater for mains failures at subscriber's premises, under emergency conditions. The carrier receiver is illustrated . . [Receiver Carrier WB200A]

This early development work used mains operated thermionic valve receivers, using similar circuits to those in household radio receivers from the nineteen fifties. The Carrier Receiver looks very much like a radio of that period. The black bottom panel houses three white and two black knobs, plus an On / Off switch.

The 1952 / 53 Report, details the results of the "Carrier Wire Broadcasting System for Civil Defence" trial. The field trial of equipment designed for distributing civil defence messages over working audio junctions and local lines was completed at the end of August 1953 after a successful run of 14 weeks. During this period, operation of the trial was under control of the Home Office who arranged for test messages to be sent out twice daily. On completion of the operational trial, the subscribers' receivers were recovered but the exchange equipments at 29 exchanges were kept in operation and have been tested at three-monthly intervals; a number of receivers were also put on life test.

The field trial showed a number of ways in which the design of the equipment could be improved and further development work has been undertaken. The design of the equipment has been modified to provide for the simplification of the facilities offered, improved performance (particularly with regard to quality of received speech) and the use of dry batteries instead of secondary batteries to operate subscribers' receiving equipment in the event of failure of the mains power supply. Further attention has also been given to the design of testing equipment.

Progress seemed very slow with many delays, the 1956 / 57 Report indicates the position five years later. Financial authority for installation of the system . . . was expected but did not mature during the year under review. Drawings, specifications and final prototypes were prepared and held in readiness.

The delay enabled further development work to progress, so by 1958 Financial authority for the scheme referred to in the 1956-57 report (page 69) was not received during the year. Work was commenced on a revised design employing transistors instead of valves, one of the principal aims being to increase greatly the duration of working in the event of mains failure.

With the cold war beginning to hot up, the E-I-C 1959 Report said Work on the redesign of the equipment to employ transistors instead of valves (1957-58 report, page 67) proceeded slowly in the first half of the year under review, but it was speeded up on indication that authority for implementing the scheme might be forthcoming. Instructions to proceed with the scheme were received in January 1959

The system designed so far was for a speech broadcast system from Police Control Centres to Warning Recipients. The next report indicates that a siren control system would be added later.

The E-I-C 1959 / 60 Report, shows that progress was now being made. Redesign of the circuits to employ transistors was completed in the year under review. The system was coded Carrier System WB 400. Authority was received for Stage 1 - comprising 2,700 exchanges, 150 control centres and 14,000 subscribers' receivers - to be completely installed by March 1962. Orders were placed for some small items of the equipment, and negotiations were commenced with three transmission equipment contractors on the design for production of the control and exchange equipments. Extensive field tests were made of the interference from radio stations that may be experienced on the system. A radio interference balancing unit was designed for use on lines containing open wire. Planning of the junction network for Stage 1 was substantially completed by the Regions and Directorates concerned. Work was commenced on a v.f. signalling system for the remote control of public warning devices as an additional feature on the Carrier System WB 400.

The first mention of using the Speaking Clock network to propagate warning messages to every police control centre was first mentioned in 1961 / 62 Report in a very guarded way. V.F. and speech equipment for a national network to feed warning information to the carrier control centres was designed and ordered.

By the 1963 Report, some parts had been installed By the end of the year orders had been placed for equipment at 254 control centres, 5,500 exchanges and 21,500 receiving points; 79 systems had been installed of which 24 had been handed over for service. Development work was continued on a system for remote control of public sirens by means of v.f. signals over the Civil Defence carrier system. Development work also continued on sub-audio signalling equip ment intended for the distribution of local call timing meter supply pulses to U.A.X.s over the Civil Defence carrier system. GPO BT staff will know this later system as WB700, which is described in a page Other Topics / Other WB's along with other wire broadcast systems, such as the WB300 for the Atomic Energy Authority which leapfrogged ahead in its implementation.

Work on the Speech broadcast system was substantially complete by 1965. By the end of the year the 250 carrier systems (WB 400), together with the associated equipments terminating the national audio network connected to the central source of information, had been completed and approximately 20,000 receivers, distributed over 5,500 exchange areas, had been connected. Additional receivers are being connected, as required by the Home Office. The design of the v.f. signalling system (WB 600), for remote control over the WB 400 networks of all power operated sirens, was completed and contracts were placed for control equipments and for 7,400 siren point receivers. Work on the siren control system was reported in 1967 Carrier System for Civil Defence. The extensions to the WB 400 system were connected and the installation of the siren control system (WB 600) was substantially completed.

Outline of HANDEL used between 1962 - 1992

HANDEL Network

UK Public Air Attack Warning Network

The United Kingdom Warning and Monitoring Organisation (U.K.W.M.O.) was set up in 1957 to give public warnings of air attack and fallout from nuclear weapons. The communications system used to convey the national attack warning from either of two command centres to 250 control points in police stations was known by the keyword HANDEL. Fallout Warnings and the eventual All Clear was the responsibility of the UKWMO, by using landlines from one of its 25 local Group HQ's to the police control points within their coverage area.

Police station control points relayed voice messages for the attack warning, fallout warning, all-clear and special tones for controlling sirens, by using radio frequency signal sent over normal telephone circuits, as a carrier. The police station control point was known as the Carrier Control Point ( C.C.P. ). The carrier had no effect on the operation of the telephone line and the avoidance of private wires (also known a Private Circuits) used by the previous system reduced the implementation cost and improved reliability.

The HANDEL and carrier network were 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 and the carrier broadcast system were 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 carrier system had two parts, the WB400 for speech broadcast and WB600 for siren control. Confusingly both used the same carrier and were actually both integral parts of one system. During the early 1980ís this original equipment was replaced by the new WB1400 system using more modern technology and addressing many 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 warning system may be found in this section by clicking the Tabs at the top of this page or the related topics push buttons at the bottom of this page.

National Attack Warning Red

The National Air Attack Warning message would originate not from military personnel but from a Home Office Principal Warning Officer ( PWO ) stationed at a location known variously as Strike Command (SC), Primary War HQ (PWHQ) or Air Defence Operations Centre (ADOC) at RAF High Wycombe. If that were to become disabled, the messages could be sent from the UKWMO Headquarters at Goosnargh near Preston, Lancashire.

Using the HANDEL network a verbal 'Attack Warning Red' message would be passed to Carrier Control Points (CCP) set up in 250 major police stations. Each CCP would pass on the alert to the public in their local area by sounding the sirens and verbal messages.

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, should both National Centres be disabled, the UKWMO Groups HQ's were also instructed to call each CCP within their area requesting they issue the Attack Warning Red.

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 much used 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 distribution amplifiers at these major exchanges would switch to the other ring circuit should the one currently in use fail, thus maintaining the time service.

When HANDEL was first installed in early sixties, 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 telephone exchanges 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 ones 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 mechanical speaking clocks were replaced by electronic units using memory devices to store the time 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 Announcements and the Speaking Clock supplied by 2 M/bit rings emanating from the B.T. Network Operations Centre near Oswestry.

Fallout Warning and All Clear

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. Even if the UK was not directly attacked, we would need to know if we may receive fallout from bombs in other European countries.

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 police station carrier control point, ask for a fallout warning to be broadcast to the appropriate district.

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 police station Carrier Control Point.

Following a National Attack Warning, if the attack failed to materialise, was intercepted or the raiders didn't use nuclear weapons, an All Clear message White may be issued at National level from SC/PWHQ/ADOC control centre.

Police Station Control Point

Carrier Network Basics

HANDEL Nuclear 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.

Carrier Control AreaNumber
Melton Mowbray071
Market Harborough078
East Kilbride309

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 multi-channel 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'.

Public Warning Receiver

In built up areas mains power operated sirens would be operated by signals sent from the CCP. These were often at WW2 siren locations. In addition to the carrier 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

WB400 Carrier Receiver

Second Generation Speaker

WB1400 Speaker Unit

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 speech 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 instruction booklet. Both sets of instructions are reproduced on their relevant pages.