Concrete acoustic mirrors can look absurd when judged from an era of radar, yet sound carried beyond visual range before radar offered a better warning system. The equipment addressed a real detection problem with the technology available at the time. Later acoustic and Doppler methods even returned to some of the same physical principles. Interwar defence policy makes more sense when the available choices are reconstructed before they are judged by what came later.
Notable Point · 8:12-9:41
Acoustic mirrors and the danger of hindsight
Britain's concrete listening structures make more sense when treated as a pre-radar answer to detecting aircraft beyond visual range.