How can sonar determine the shape and distance of an object?

Sonar measures the distance of an object by sending out a ping and listening to the echo. Sonar on a submarine will have many hydrophone locations to tell the listener the direction of the object, and by measuring how many hydrophones the echo hits, where, and when, you can use math to discover the approximate length of what you are listening to. Modern day sonar will often do the math for you and show you a radar like screen of dots where the sonar has heard an echoing ping within a certain distance. Also, once any specific ship has been heard once by a hydrophone and identified as a certain class vessel, the sonar crew can use passive sonar (no pinging. Listening only) to hear the screws turning in the water and can usually tell the experienced sailor (or the modern computer database) what types of ship it is likely to be. In the movie "The Hunt for Red October" the sonarman on the american submarine heard what the computer called "seismic activity" and identified this as, in fact, the Red October. This first identification, which took some time, enabled him to identify the sub faster in the future. There are however disadvantages to sonar. In modern times almost all military naval vessels have at least some basic form of sonar. As soon as somebody on a submarine sends a ping,, veryone else in the area knows you're there. Some ASW tactics involve planes dropping hundreds of passive and active sonobouys all over the area. The submarine will usually attempt to hide from the active sonobouys which will often lead it right towards a passive sonobouy.