Can you hear it yet?

We were lucky enough to be at Dungeness on one of the few days of the year that the Sound Mirrors are open to the public - normally, you can see them from a distance, but they are marooned on an island so it's not possible to get close. The Romney Marsh Rangers and volunteers did an excellent job, providing information and guided talks.

Various sound mirrors were built by the Government and Ministry of Defence in the early 1930s as a method of hearing enemy aircraft approaching over the Channel. Each mirror, of which there were various different designs (in the background of the blip is a 200ft parabolic wall version) had a listener with a stethoscope who's job it was to listen for approaching aircraft. They were built back from the sea so the sound of the sea didn't disrupt their purpose. Experiments continued for a while, with multitudes of test flights by the RAF but were eventually abandoned after Radar was developed.

The largest mirror here is a 30 foot concave dish, the smaller, earlier model (completed in 1928) is 20 foot.

Now, they're a fascinating curiosity .

Some were built abroad as well - there's an intact parabolic wall in Malta, apparently.