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, the principle of which is to integrate the acoustic energy coming from the source in a relatively wide frequency range ( $$\text{>} 100\text{Hz}$$ ). This example dates from the early development of passive underwater detection (PUD), which roughly covers the period from 1930 to the late 1950s. Although the first applications of passive listening already existed at the end of the 19th century, their use was limited until the dawn of the Second World War, when ranges...