A radar is an object detection device that uses radio waves to determine the speed, altitude and direction of objects. Radio waves, or microwaves, are transmitted from a radar dish. These waves then continue in their paths until they hit an object. A small bit of the wave is returned to the transmitter, making it possible to determine the speed and other characteristics of the object. Radar is a very important tool in the military as it is used to detect aircrafts, vehicles and missiles.
Sonar is a very common technique used in submarines and other underwater vessels. It uses sound propagation to detect objects in the water. This is done by emitting sound pulses and listening for echoes. Sonar is also commonly used in the military to determine the location of other vessels.