Sound mirror FAQ

Here are the answers to a few frequently asked questions. Feel free to drop me a message with any queries – though I must admit that I’m not in any sense a real expert on the mirrors. I just think huge lumps of funny-shaped concrete are quite interesting.

What on earth…?

An early warning structure built during and after WWI along the south and east coasts of England. Sound detecting acoustic dishes and walls could detect the sound of approaching enemy aircraft at a distance of 8 to 15 miles.Royal Commission on the Historical Monuments of England

How can I visit the mirrors?

There is location information and travel details on the indvidual pages for each of the mirrors.

The RSPB organises open days at the three mirrors at Denge (Greatstone, near Dungeness). These are the only way to get access to those mirrors, which are now marooned on an island in the middle of a flooded gravel pit, and can only be accessed by a swing bridge which is locked open at all other times. Seriously, there is no other way in.

Did the sound mirrors work?

In the sense that the mirrors did allow aircraft to be detected before they could be seen, yes they did. But the range of the mirrors was rather short, at less than 25 miles, and as aircraft got faster the mirrors didn’t give enough warning to be useful. Radar rendered the mirrors completely obsolete – it could do the job much better.

The widening margin is an analysis by Brett Holman about how useful they might have been. Subject to various assumptions, he calculates that by the 1930s sadly the acoustic mirrors wouldn’t have made much difference – a margin of only about 10 minutes, not much improved on the 5 minutes with no warning system. Of course, even a few minutes’ extra warning was worth having, but the Air Ministry was right to terminate development of the acoustic mirror network in order to concentrate on the far more promising radar.

Where can I fnd out more?

The book Echoes from the Sky by Richard N Scarth (published by Hythe Civic Society) is the definitive book on the post-WWI mirrors, including Denge and Malta. It gives a detailed history of the sound mirrors and associated research projects, and is essential reading if you are interested in the story behind the mirrors. Unfortunately it is now out of print, and the Civic Society asks people not to e-mail them to try to buy a copy – they’ve none left.

Information on the northern mirrors is very sparse. Anyone know more?

Did you know there was another mirror at <insert name of place>?

If it isn’t listed, then no, not yet – but I’d love to know about it. I only found about the Seaham mirror because someone now living in Australia remembered playing on it as a child. It is certainly possible that other mirrors existed – one is rumoured to have existed at Hartlepool, and Felixstowe has been suggested.

What other names have they been known as?

Sound mirrors, acoustic mirrors, listening posts, ears, concrete ears, il widna (the ear in Maltese), detection post, acoustic wall, sound dish.

Where there any mirrors outside the UK?

There is one at Maghtab in Malta. Others were proposed but not built elsewhere in Malta and in Singapore. This photo shows something miroror-like in Gibraltar, but I haven’t pinned down what it is yet.

Would you like some more pictures?

Yes please – some of my pictures are pretty awful. There is also a Flickr group, where more pictures would be very welcome.

My album/artwork includes sound mirrors – would you like some details?

Yes please!

I’m looking for some high-resolution pictures – can you help?

Send me a message with details of what you need, and I’ll see if I can help find something.

Who are you?

I’m Andrew Grantham.

Why a website on sound mirrors?

Back in the mists of time I was vaguely aware of the Denge mirrors, and thought I had also heard rumours of one near Spurn Head. On a visit to Dover castle I flicked through a copy of 20th Century Defences in Britain, and saw a black and white picture of the Kilnsea mirror.

The next time I was back in East Yorkshire I went to have a look at it, and took some photographs. I put the pictures on a webpage, and soon found there was a surprising amount of interest in the mirrors, but very little was known about them.

In recent years there has been a surge of interest in 20th century military archaeology, with assorted books, websites, televison programmes and so on. People started sending me pictures and information about other mirrors, and it soon became clear that there were more of them than the few printed sources suggested existed.

More exotically, artists, musicians and TV producers got in touch wanting to know about the mirrors with a view to using them in their work.

The website is broken!

Send me a message with details and a link to the page(s) and hopefully I’ll be able to fix it. For anyone wondering, the website is basically a slightly fiddled-with version of a WordPress blogging package. WordPress is free, a little fiddly to install, but customisable and seems to work well.

What other websites do you have?

For fans of the obscure, I have some webpages about railways in Afghanistan and Iraq, a few random travel articles, and the website of the Hull & Barnsley Railway Stock Fund, a railway preservation group.

Can I link to this website?

Yes, of course. But please ask before using any of the pictures – many are not my copyright, but belong to the photographers and are used with permission.

I would like to buy a 200ft sound mirror – will you send details of your bank account to my e-mail address?

Someone really did e-mail me asking this :-)

One thought on “Sound mirror FAQ

  1. We’re coming to see the mirrors at Dungeness on 19th July. I apologise for the fact that this question leapt to mind, but here goes: did Dr Who ever film there?

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