Denge sound mirrors or listening ears. Concrete structures designed to pick up enemy aircraft coming from the channel. Built 1924 on Romney Marsh Stock Photo - Alamy
Folksonomy | Sound Mirrors: Dead-end Technology
The Concrete “Sound Mirrors” That Influenced WWII, Science, And Design
Greatstone Sound Mirrors – Greatstone, England - Atlas Obscura
The concrete blocks that once protected Britain - BBC News
Denge sound mirrors | Sound Mirrors
Sound mirrors hi-res stock photography and images - Alamy
Before Radar, These Giant Concrete “Sound Mirrors” Were Used To Detect Incoming Enemy Aircraft | History Daily