targets, and from the 1880s, they were widely used on ships in order to monitor the water area in tuman -e and, accordingly, you could hear the sounds of the engines of the engines in the first world war, they also detected air targets eh, also an interesting fact would probably be to note that the first airplanes that appeared in the first world war , they were, in principle, radio permeable, they were not they reflected, that is, they did not see radars, radar did not see them in principle, that is why when the first radars appeared in the 30s and they were already inefficient and acoustic sensors, they were still used for a very long time, even during the second world war, we basically used from that of all the experience that i have just listed, we used only the fact of the selection of materials, because when they began to implement them, we quickly realized that metal is not the best material for the implementation of such an acoustic direction finder it introduces a lot of um interference changes to the signal itself and the sound itself and that's why we already had a certain id