466K views · 13K reactions | These 'sound mirrors' near Lydd in Kent were built in the late 1920s as part of Britain’s early air defence system. ️ Designed to detect enemy aircraft by capturing sound waves, they provided an early warning before an attack. Advances in radar eventually made the sound mirrors obsolete, but they remain fascinating reminders of an innovative era in military technology. Today, they’re protected as scheduled monuments. | Historic England | Facebook