These massive concrete acoustic mirrors, or “listening ears,” were built in England between the world wars to monitor the skies for the telltale sounds of airborne invasion. Their parabolic shape collected and magnified sound waves in the air over the English Channel and directed them at a microphone positioned just in front of the parabola. The mirrors effectively gave Britain a fifteen-minute advance warning of an impending attack. A precursor to radar, the dishes were made obsolete at the end of the 1930’s and have been left to the elements. 📸: Photo by @forgottenheritage.