Paul Langevin

Sonar

Langevin’s 1915 sonar was the first active underwater echo-ranging system. It used electrostatic and quartz piezoelectric transducers to send and receive ultrasound. Distance was calculated from signal time-of-flight. Though patented and physically demonstrated, it did not become operational before World War I ended. Electrostatic transducers were soon abandoned; quartz piezoelectric methods endured and scaled. The invention established the core mechanism of modern sonar — but delivered no tactical utility in its intended conflict.