Powered flight

Louis Bleriot was the first person to fly across the channel in 1909; this leap forward in aviation technology meant that Britain’s status as an island nation was not enough to prevent attack from Europe. The 22 mile crossing to France no longer offered protection from attack and new ways of protecting ourselves were required.

The early story of sound mirrors is not clear, but it is believed that the first experiments were conducted in 1915. The first mirrors or ‘dishes’ were cut directly into the chalk to try and reflect the sound. These early beginnings soon gave way to larger and more complicated structures made of concrete.

How sound mirrors work

Sound mirrors worked using a curved surface to concentrate sound waves into a central point, which were picked up by a sound collector and later by microphones. An operator using a stethoscope would be stationed near the sound mirror, and would need specialist training in identifying different sounds. Distinguishing the complexity of sound was so difficult that the operators could only listen for around 40 minutes.

Fan Bay Sound Mirrors

There are two mirrors at Fan Bay; the first constructed in 1917 is believed to be one of the oldest surviving sound mirrors in the country; the second is larger and was built at some point in the 1920s. Both mirrors were initially cut into the chalk and lined with concrete to form the distinctive dish shape.