Who knew piezoelectricity? Rutherford and Langevin on submarine detection and the invention of sonar

During World War I, submarine detection presented a strategic technological challenge, which inspired, among others, the invention of new methods and the employment of a hitherto unused scientific phenomenon. Two prominent physicists, Ernest Rutherford and Paul Langevin, independently suggested the use of this phenomenon: piezoelectricity. Yet they employed it in different ways, leading Rutherford to a useful, if limited, measuring device and Langevin to sonar. Contrary to a claim that is commonly made, Rutherford's work did not lead to sonar. These different results originated on one hand in diverging goals of the two physicists, and on the other in Langevin's more extensive knowledge of and practice with piezoelectricity, which allowed him to manipulate the crystals and contrive the novel ultrasonic design required. Nevertheless, previous encounters with the effect and prior familiarity with it were crucial for its employment by both. This journal is