Listing of sound mirrors urged: Oliver Gillie reports on the pre-radar detection devices that enthusiasts want to see preserved

HUGE CONCRETE sound mirrors used before the days of radar to listen for the approach of hostile aircraft should be scheduled as national monuments, according to enthusiasts. Already several have been demolished, but at least seven remain - four of them in Kent, which provided the most direct route for German bombers sent to drop their load on London.

Dave Collyer, a member of the Kent Aviation Historical Society, said: 'We lost one of the mirrors, on the Isle of Sheppey in the 1950s due to erosion, another at Greatstone has fallen over after being undermined by gravel extraction, and a third at Lydden Spout near Dover was demolished because the local authority thought it was dangerous.'

The sound mirrors were all placed on cliffs looking out towards the continent where they provided an early warning of approaching enemy aircraft. They are about 20 to 25ft high and as much across, with a concave spherical surface. Their large size and strong shape gives them a sculptural impact apart from their interest as monuments of early military technology.

A microphone was moved about in front of the concrete mirror while a man with earphones listened to the sound. By noting the position of the microphone where the sound was loudest, the direction and height of approaching aircraft could be calculated.

'The first two sound mirrors were built near Dover in 1917,' Mr Collyer said. 'They could pick up the sound of the Gotha long-range bombers which raided London during the First World War. More of the mirrors were built between the wars. The idea was to have a chain of them round the coast. In practice their maximum range was 20 miles. They were useful for finding the direction, but they were never accurate in obtaining the height or size of the attacking force.'

Mr Collier knows of only four left in Kent, one near Spurn Head, Humberside, and two near Redcar in Cleveland. One of the mirrors, at Greatstone, near Hythe in Kent, is a 200ft-long wall mirror built in a parabolic shape, but the others are spherical in shape. Some, including one of the parabolic type, were also built in Malta where one is now part of a pig farm.

'The sound mirror technology became obsolete as bombers became faster, but the idea was kept alive as a cover for radar,' Mr Collyer said.

'The press were called in to photograph them. And when the Germans started jamming our radar, attempts were made to use the sound mirrors again. We think that preservation orders should be put on them and plaques to explain to people what they are. They are part of our history.'

(Photograph omitted)

Start your day with The Independent, sign up for daily news emails
Sport
sportSo, how closely were you paying attention during 2014?
Arts and Entertainment
Dennis speaks to his French teacher
tvThe Boy in the Dress, TV review
News
One father who couldn't get One Direction tickets for his daughters phoned in a fake bomb threat and served eight months in a federal prison
people... (and one very unlucky giraffe)
Arts and Entertainment
Joel Edgerton, John Turturro and Christian Bale in Exodus: Gods and Kings
film
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
News
i100
Arts and Entertainment
The Plaza Theatre in Atlanta, Georgia was one of the 300 US cinemas screening
filmTim Walker settles down to watch the controversial gross-out satire
Arts and Entertainment
Amy Adams and Christoph Waltz in Tim Burton's Big Eyes
film reviewThis is Tim Burton’s most intimate and subtle film for a decade
Life and Style
Mark's crab tarts are just the right size
food + drinkMark Hix cooks up some snacks that pack a punch
Arts and Entertainment
Jack O'Connell stars as Louis Zamperini in Angelina Jolie's Unbroken
film review... even if Jack O'Connell is excellent
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: Senior Marketing Executive- City of London, Old Street

£40000 - £43000 per annum + benefits: Ashdown Group: Senior Marketing Executiv...

Ashdown Group: Marketing Manager

£40000 - £43000 per annum + benefits: Ashdown Group: An international organisa...

Ashdown Group: Internal Recruiter -Rugby, Warwickshire

£25000 - £30000 per annum: Ashdown Group: Internal Recruiter -Rugby, Warwicksh...

Ashdown Group: Marketing Manager/Marketing Controller (Financial Services)

£70000 - £75000 per annum + benefits: Ashdown Group: Marketing Manager/Marketi...

Day In a Page

Aren’t you glad you didn’t say that? The worst wince-and-look-away quotes of the year

Aren’t you glad you didn’t say that?

The worst wince-and-look-away quotes of the year
Hollande's vanity project is on a high-speed track to the middle of nowhere

Vanity project on a high-speed track to nowhere

France’s TGV network has become mired in controversy
Sports Quiz of the Year

Sports Quiz of the Year

So, how closely were you paying attention during 2014?
Alexander Armstrong on insulting Mary Berry, his love of 'Bargain Hunt', and life as a llama farmer

Alexander Armstrong on insulting Mary Berry and his love of 'Bargain Hunt'

From Armstrong and Miller to Pointless
Sanchez helps Gunners hold on after Giroud's moment of madness

Sanchez helps Gunners hold on

Olivier Giroud's moment of madness nearly costs them
A Christmas without hope: Fears grow in Gaza that the conflict with Israel will soon reignite

Christmas without hope

Gaza fears grow that conflict with Israel will soon reignite
After 150 years, you can finally visit the grisliest museum in the country

The 'Black Museum'

After 150 years, you can finally visit Britain's grisliest museum
No ho-ho-hos with Nick Frost's badass Santa

No ho-ho-hos with Nick Frost's badass Santa

Doctor Who Christmas Special TV review
Chilly Christmas: Swimmers take festive dip for charity

Chilly Christmas

Swimmers dive into freezing British waters for charity
Veterans' hostel 'overwhelmed by kindness' for festive dinner

Homeless Veterans appeal

In 2010, Sgt Gary Jamieson stepped on an IED in Afghanistan and lost his legs and an arm. He reveals what, and who, helped him to make a remarkable recovery
Isis in Iraq: Yazidi girls killing themselves to escape rape and imprisonment by militants

'Jilan killed herself in the bathroom. She cut her wrists and hanged herself'

Yazidi girls killing themselves to escape rape and imprisonment
Ed Balls interview: 'If I think about the deficit when I'm playing the piano, it all goes wrong'

Ed Balls interview

'If I think about the deficit when I'm playing the piano, it all goes wrong'
He's behind you, dude!

US stars in UK panto

From David Hasselhoff to Jerry Hall
Grace Dent's Christmas Quiz: What are you – a festive curmudgeon or top of the tree?

Grace Dent's Christmas Quiz

What are you – a festive curmudgeon or top of the tree?
Nasa planning to build cloud cities in airships above Venus

Nasa planning to build cloud cities in airships above Venus

Planet’s surface is inhospitable to humans but 30 miles above it is almost perfect