The Air Raid Siren
Air Raid Precautions badge

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 for wear on civilian clothing
                           ARP lapel badge
ARP Whistle
                              ARP whistle
ARP Rattle
                        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.

Carter Siren Advert

Advertisment from Daily Mail September 4 1939

Sound Generation.
The electrically driven sirens composed of an electric motor, usually 3 phase, with shafts at either end on which were mounted impellers or fans. One end having 10 blades and the other having 12. Around these two impellers were housings with 10 and 12 slots to match the impellers. The impellers were so designed that upon rotation
they drew in air at the end and forced it out through the corresponding slots in the housing circumference.

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.

WW2 siren
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.

Extract from Ex-Govt Catalogue c1956

Air Raid Warning Control Units

Conrol unit

These units were originall used for Air Raid Warning remotely operated from electric light power stations being directly connected with the main AC supply at customer's premises and operated either by a DC bias voltage or by audio frequencies injected into the main supply.
Consisting of tuned relay with two reeds which in turn operates a 10 amp mercury switch through a train of gear wheels by means of a ratchet. A frequency of 427cps will operate the switch to the on position and 396 cps will operate the switch to the off postition. Contained in a waterproof cast iron box 5 1/2" x 5 1/22  x 4" deep
Manufactured by GEC or Standard Telephones and Cables.
Price 12/6d, postage 3/6d

Air Raid Sirens in London

There are two  well known sirens in London
Waterloo railway bridge siren
 The Waterloo siren is situated on the bridge 
 support on the north side of the bridge 
 that crosses York Road. 


Kesington Gardens Siren
 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.
Close up of Kensigton Gardens siren
 Detail of Kensignton Gardens siren.


The Cold War

Post war siren
The Siren

There was a continuous programme of care and maintenance and over the years most of the original sirens would have been replaced with later models.
This one being manufactured by Castle Castings around 1987/8.

Click here to see picture of the The Control Panel.

The contractor who had the job of removing them in Sussex kindly donated the siren to the
Tangmere Military Aviation Museum
and was restored
by Penfolds of Barnham
(Restored and I think the Broad Arrow is poetic licence!)

Sirens at Kelvedon Hatch Secret Nuclear Bunker in Essex

Control box

Click here to see picture of electrically driven siren in the Kelvedon Hatch collection
Visit the Kelvedon Hatch website

For use in the Second World War it was only necessary to provide Red and White Warnings.

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


 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 

The need for the Grey Warning was withdrawn in 1968.

Home Office Type 447
Hand Operated Siren
The Home Office Type 447 siren was produced from the early 1960's by two companies, the well known siren manufacturer "Carter" and "Secomak" - (Service Electric Co Ltd).

The different manufacturers can be identified easily.

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

Carter Siren - note tripod stand

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

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

Secomak siren - note tubular legs.

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

Secomak instruction label

Instruction Card Text:-

Instructions for Use
Secomak assembly instructions

1. Take the siren from its crate and assemble it (see diagram). Check that the turning handle rotates freely, and that the twist grip shutter control on the steading handle opens and closes the shutter on the side of the siren body.

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)

Care and repair of the The Home Office Type 447 Hand Operated Siren.

Click here
to visit


Hand operated Type 447 Siren in packing case

Secomak siren in packing case

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

(Twisting the sleeve on the steadying handle controls the shutter)

Packing case marked:
Manufactured by Service Electric Co Ltd 1963

Hand Operated Siren at
Kelvedon Hatch Secret Nuclear Bunker in Essex

Pictures of boxed siren manufactured by Carter & Co
Click her to see picture of boxed siren
Click here to see picture of Carter's label

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 in Germany.

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

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