About the book: 1962 / Our generation witnessed an extraordinary victory of the human mind - the beginning of penetration into space. Fascinating, full of tempting prospects for interplanetary travel and discoveries open up before young people. But there are also many unexplored “white spots” on our “inhabited” planet Earth, among them the World Ocean, almost unknown to its entire depth, with its underwater mountains and depressions, with its flora and fauna, with their own physical laws. In its study, hydroacoustics is of great benefit - a relatively young science with a great future. This science is of great applied importance. Modern submarines cannot do without hydroacoustic devices, which are the “ears” and “eyes” of submarines. Hydroacoustic instruments are also necessary for navigation and fishing. The author talks about what hydroacoustics is, how hydroacoustic instruments are designed, and how hydroacoustics serves us for peaceful and military purposes..