Before radar, Britain tried to hear enemy bombers coming using giant concrete ‘ears’

Britain’s Denge Sound Mirrors, three concrete structures on the Kent coast built between 1928 and 1930, were designed to catch the drone of approaching bombers and give defenders a few extra minutes of warning. Led by physicist Dr William Sansome Tucker, the project followed heavy World War 1 air raids on coastal towns. Faster aircraft, background noise and the arrival of radar made the mirrors obsolete by 1939.