English: These Sound Mirrors represent Britain's first attempt at an Air Defence System designed to magnify the sound of approaching enemy aircraft thus buying an extra 5 to 10 minutes warning to enable our Fighter aircraft to get airborne in the hope of intercepting them. Thankfully they were not put fully to the test as Radar came along just in time and superceded this less effective system. The concrete mirrors were constructed before the lakes formed following gravel extraction after WW11. In order to get closer to them you have to make an appointment with the local Wildlife Trust who will open the gate over the bridge. They are now Grade 2 Listed Buildings so will take there own sweet time eroding away slowly in the salty air. I have attached a link giving more information above.