UK Attack Warning System Overview

The Warning Message

It was planned to advise the public of the onset of attack, subsequent fallout and all clear by issuing three colour coded messages -- Attack Warning RED, Fallout Warning BLACK and Attack Message WHITE. The warning recipients had an instruction card telling them how to issue the public warning. This card is reproduced in a sub-topic.

Getting the Message Across

The Air Attack Warning message from Strike Command was delivered to the HANDEL phones at the Police Station. This utilised the Post Office Telephones (became BT) Speaking Clock distribution system. Consisting of a "Ring" of lines between major exchanges designed to raise an alarm if the ring failed. This provided a ready made, secure (against breakdown) system of distributing the Attack Message around the country. At the time I worked on the system (1978-1981), the location of Strike Command was unknown to me, so I have no idea how the warning message got onto the Speaking Clock distribution system. The Royal Observer Corp. (ROC) Group Headquarters for that District also had a line to the police station terminating on the HANDEL phones. This would be used to pass the Fallout Warning messages and eventually the All Clear.

This is a two stage system. Onward distribution of warnings required human intervention at the police station to retransmit the message. Neither Strike Command nor the ROC had any way of alerting the end user at the warning point. The police station control panel could be used to issue verbal messages and activate electric mains operated sirens.

At the Police Station, a 72 kHz carrier, modulated with speech or tone signals was generated in the Carrier Control Point equipment. This was distributed via the main telephone exchange (Carrier Control Exchange) for the area to all the warning points. To provide security against a fault going unnoticed, the carrier was sent over lines used for normal telephony. Filters separated the audio from the carrier so both could be used simultaneously.

In the Topics that follow this page the carrier system will be described in more detail. The verbal warning system is the WB400 and its associated siren control system the WB600. These are the two parts of the equipment I was most familiar with. During the mid 1980's the WB400/600 was upgraded and replaced by the WB1400. All of these systems are described in later topics

Prior to the introduction of the carrier system, the sirens were controlled by a system of sending direct current signals down private circuits from the police station to the siren point. A description of System E, may be found on the cross reference link.

Warning Districts

The country was divided into 250 Warning Districts each with its own Carrier Control Point. The district boundary followed closely the telephone charging boundary for the Carrier Control Exchange. The ROC Group HQ monitoring the fallout in the district via its hilltop ROC posts. The HQ was connected by landline to a HANDEL phone, so the police could issue fallout warnings

A Myth

You may read that the Warning System consisted of broadcasting a 72kHz carrier 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 subbrit news group too.

From the diagram you can see this is not strictly true. The speaking clock only distributed audio. Two pairs of wires connected the Carrier Control Exchange to the Police Station, these carried both the Audio for HANDEL, to the Police Station and the carrier from the Police Station. The Speaking Clock distribution did not distribute the carrier, as this was generated at each Carrier Control Point (Police Station).