Submarines in ww2 had a form of \"passive sonar\" which was a directional underwater microphone (hydrophone). Using the hydrophone, the bearing to sources of sound, such as ships, could be determined and a good operator could tell the difference between different types of ships by the sounds that their props made. The use of this device was entirely manual, and of course there was no computer to analyze the sound. Range determination was only qualitative (e.g. near or far), a good operator could hear the sound volume change and determine whether a contact was approaching or receding.

The data gathered by hydrophone was not generally good enough to aim torpedos with, but could be used while submerged deeper than periscope depth, allowing the sub commanders to keep track of surface ship activity.

The first forms of active sonar were implemented part way through ww2 by the anti-sub forces. the first of these was \"ASDIC\" which was a pinger with a directional hydrophone to listen for the echo. direction and distance were able to be determined, but the systems were still fairly primitive compared to modern phased array systems