Britain's Acoustic Mirrors of War

The Deputy Dog website has a very cool piece on Britain's acoustic mirrors. The acoustic mirrors were used before radar as early warning devices in Britain. They were built in the 1920s-1930s and featured different shapes in order to test their abilities. Although the acoustic mirrors were not quite as effective as the creators had hoped, they did implement Britain's early radar systems by being able to detect range and direction of incoming aircraft for over 20 miles.

For all of the images check out the link below.
There is also a link below to a short and silent video of the acoustic mirrors on Youtube.