1. Presentation of the three examples

1.1 First example: bow sonar range of the heavy cruiser Prinz Eugen

The first example is that of a broadband (BL) chain, whose principle is to integrate the acoustic energy coming from the source in a relatively wide frequency range (> 100 Hz). This example dates back to the early development of passive DSM, which roughly covers the period from 1930 to the late 1950s. For, although the first applications of passive listening already existed at the end of the 19th century, their use was fairly limited until the dawn of the Second World War, as ranges were deemed insufficient