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HANDEL was the code-name for the UK's National Attack Warning System in the Cold War. It consisted of a small console consisting of two microphones, lights and gauges. The reason behind this was to provide a back-up if anything failed.
If an enemy air strike was detected, a key on the left hand side of the console would be turned and two lights would come on. Then the operator would press & hold down a red button and give the message:
|“||Attack warning RED! Attack warning RED!||”|
The message would be sent to the police by the telephone carrier wave frequencies used for the speaking clock, who would in turn activate the air attack sirens using the local telephone lines. The rationale was to kill two birds with one stone, as it reduced running costs (it would most likely be used only once in its working life, though it was regularly tested) and the telephone lines were under constant test by sharing with a public service. That means a fault could be detected in time to give a warning.
|Message||How it's received||Action to be taken||Notes|
|Attack warning||Warbling note followed by message: "Attack warning RED!" This would be followed by a control signal, activating the powered ones[clarification needed].||Sound warning by activating sirens, the attack warning will be a rising and falling note.||Attack warning will be broadcast on all television and radio stations.|
|Fall out warning||High pitched pip signal followed by a spoken message. For example: "Fallout warning BLACK, London!"||Fire warning maroon (firework) three times. Though in some areas, it can be three gongs or whistles creating one long note followed by two short notes forming the morse note "D-".||Fall out warning will be broadcast on the radio.|
|Fall out expected within the hour||High pitched pip signal followed by spoken message. For example: "Fallout warning GREY, Canterbury!"||Sound siren producing one long note but interrupted in short succession. Can also be given by church bells or word of mouth from the police and civil defence wardens||Fell out of use by the late 1960s|
|All clear||High pitched pip signal followed by a spoken message: "Attack message WHITE!" A steady control tone will activate the powered ones.||Sound siren giving a steady note||Further warnings may be broadcast on radio, along with information on aid for survivors and morale boosting broadcasts (There was also a "confidence tone" that demonstrated the system was working and told you to stand by for a warning at anytime).|
A HANDEL Warning console can be seen at the Imperial War Museum in London among their cold war exhibits, alongside the warning apparatus used by Kent Police (which was located at Maidstone police station to activate the sirens).
See also 
- Imperial War Museum (2011). "Signalling Equipment, Handel Unit 1A, British". Collection Search. Retrieved 10 September 2012.