The concrete Abbot’s Cliff Sound on Abbots cliff on the 17th of January 2022 outside of Folkestone, United Kingdom. Sound mirrors were a forerunner of radar, they were an acoustic early warning system built on the south and North East coasts of England between 1916 and 1930. They were listening ears providing an early warning for incoming enemy aircraft. (photo by Andrew Aitchison / In pictures via Getty Images)
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