Before the Second World War there was no system for warning the general population of an impending air raid other than with hand bells, rattles and whistles as had been used in the Great War.

ARP lapel badge

ARP whistle

ARP Air Raid Rattle

In 1938-9 a national warning system based on sirens to warn of air attack was implemented.

Two types of siren were used, manual hand operated used in rural areas or temporary military and civillian sites and electrically operated for use in urban areas.

The manually operated type were portable and included a lightweight stand and a single hand turned impeller or fan which produced one note, the frequency of which depended on the speed of which the handle was rotated.

The electrically operated type were fixed and usually mounted on the top of a high building often a Police Station, Fire Station or Town Hall. If there were no convenient building, on a high pole.

Due to the design of the impeller and its housing the air output was cut on and off alternately thus producing the basis of sound production.

This is an illustration from a 1948 publication
and would have been typical of the type installed during the Second World War

Assuming a motor rotational speed of 2840 rpm the output frequency would be 473.33 and 568 Hertz, a sound that would become very familiar to civilians 1939-1945. (It used to scare the wits out of me!)

To convey a state of "ALL CLEAR" the siren was switched on to produce a steady note. To convey a state of "TAKE COVER" a device was wired into the motor circuit which cut the power supply for a short while at intervals thus allowing the motor speed to drop and then rise again when reconnected.

These devices were commonly supplied with two push buttons.
One, "TAKE COVER" the Red Warning, which brought into use the automatic cut-outs.
The other  White Warning for "ALL CLEAR" or "RAIDERS PAST" which over-rode the cut-outs and produced
a steady note.

There are two  well known sirens in London

	The Waterloo siren is situated on the bridge   support on the north side of the bridge   that crosses York Road.
	The Kensington Gardens siren is at the   just about opposite Queensway tube   station on the Bayswater Road.   The Black Lion Gates park gates are nearby.
	Detail of Kensignton Gardens siren.

However as the system was maintained after the war it was necessary to introduce a third warning of "NUCLEAR FALLOUT". This became the Grey Warning which was signalled on the manually operated sirens by having a shutter fitted across the air output which when closed would cause the sound output to cease.

A Grey Warning lasted 2 ½ minutes comprising 5 turns with the sound "on" and 5 turns with the sound "off". Twisting the sleeve on the steadying handle controlled the shutter.
This warning system was possibly abandoned in 1968.
 

Extract from Civil Defence Handbook No. 10  "Advising the Householder on Protection against Nuclear Attack"  Published by HMSO 1963  RED - Siren (rising and falling note) Imminent danger of attack.  GREY - Siren (interrupted note of steady pitch) or Church bells (or, in Scotland, oral or whistle message)                Fall-out expected in an hour.  BLACK - Maroon, gong or whistle sounding a Morse ‘D’ – dash dot dot. Imminent danger of fall-out ALL CLEAR – Siren (steady note) No threat of air attack or fall-out.

 

Extract from "Householder’s Survival Guide"  Published by West Sussex County Council  2nd Edition 1980  OFFICIAL WARNINGS OF ATTACK  ATTACK imminent – Sirens will sound a rising and falling note. All radio and TV programmes will  be interrupted to give warning  FALLOUT warning – Three bangs or whistle blasts on quick succession.  ALL CLEAR – Sirens will sound a steady note. If your area has received fallout then it is unlikely a general   All Clear will be issued since some hazard may still persist even after the end of the air attack. In these  circumstances you will be told of release procedures either by word of mouth by reconnaissance groups or by   radio.

The need for the Grey Warning was withdrawn in 1968.

The different manufacturers can be identified easily.

The Carter has tripod angle iron legs as shown in picture below.

The Carter siren internally is of superior manufacture with ball race bearings.

The Secomak has four tubular legs as shown in picture below.

 The hand operated Home Office Model c1962
Type 447 manufactured by Secomak
(Littlehampton Museum)

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Instruction Card Text:-

UNITED KINGDOM WARNING AND MONITORING SYSTEM
HAND-OPERATED SIREN
Instructions for Use

2. The siren should be sounded in a position which the operator can get to immediatley, but in the open away from buildings and trees, or if possible above ground level (for example on a flat roof).

3. RED WARNING Imminent danger of attack.

The signal to be given is a rising and falling note lasting one minute. Ensure that the shutter on the siren body remains open. Rotate the turning handle, applying full pressure for the first five turns; for the next five turns relax the pressure; then again apply full pressure for five turns, and so on for one minute.
After sounding the RED warning, bring the siren back under cover, if practicable.

4. GREY WARNING Fallout expected, but not for one hour.

The signal to be given is an interrupted note of steady pitch lasting for two and a half minutes. Rotate turning handle as fast as possible at constant speed, and while doing so operate the twist grip control on the steadying handle so that the shutter is open for five turns, then closed for five turns, and so on for two and a half minutes.

5. WHITE WARNING All clear (no threat of air attack or fallout).

The signal to be given is a steady note lasting for one minute. With the shutter open rotate the turning handle as fast as possible at constant speed for one minute.

(The crate that this siren instruction card was taken from was dated 1962)

Click to see picture of siren assembled and with shutter open.
Click to see picture of siren assembled and with shutter closed.

Due to their isolated locations the electrically operated sirens were subject to icing up. Fitting heaters solved this. Nesting birds presented another problem; this was solved by wire netting.

Although no doubt responsible for saving countless lives, the coverage by this type of warning in an environment of rising background noise and increased home insulation, particularly double glazing, was questioned.

During the Cold War period there were 7000 electrically operated and 11000 hand operated sirens.

With the wider use of radio and television communication the system based on the siren was abandoned in 1992.

A few lasted a little longer as flood warning and other local emergency purposes in some areas.

The Historic Dockyard in Portsmouth still have a siren and sound it periodically. I hope to locate, determine type and purpose and photograph it soon.

My thanks to the staff at Tangmere Military Aviation Museum for their interest and help.

Sirens are common in rural Germany and are used to alert the Freiwillige Feuerwehr (Volunteer Fire Service) and for any other Emergency.

Click here to see the siren atop the local government offices of Nachterstedt, to the east of the Harz mountains
Click here for a close up

Click here to see the siren mounted on the roof of the Town Hall in Buggingen in the Black Forest.
Click here for a close up.

Siren in France.
Click here to see French Siren overlooking Nice Harbour.

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All colour pix © Roy Smith
Page updated 21 November 2004