Sound Navigation and Ranging (SONAR)

Sonar is used to find and identify objects in the water. Some types of sonar can be used to calculate distance to objects by measuring the time between when a sound wave is sent out and when the reflected sound, or echo, is received. Navy Sailors use sonar to detect submerged objects such as submarines and mines.​

The ocean is a very noisy place, full of sounds from natural sources like marine animals, breaking waves, rain, lightning, and earthquakes, to man-made sources like ships and seismic exploration. This makes listening for enemy submarines extremely difficult.

It takes specialized training and lots of practice to be able to find ultra-quiet submarines in this noisy environment. Modern submarines are designed to be extremely quiet, with weapons that can fire from long distances. 

Passive Sonar

Passive sonar uses specialized transducers called hydrophones (or underwater microphones) to listen to sounds in the ocean. These hydrophones convert sounds into electrical signals that are then sent to a computer for a sonar operator to look at and listen to. Passive sonar does not transmit sounds into the water and allows Navy Sailors to detect objects without giving away their position.​

Active Sonar

Active sonar is the most effective means available for locating objects underwater. Active sonar sends out a pulse of energy that travels through water, reflects off of an object, and returns to a receiver. Active sonar has the ability to locate objects that are too quiet to be detected using passive sonar technology.​


Humans developed sonar by studying how some animals navigate and detect prey. Some marine mammals, such as dolphins, use a form of active sonar called echolocation. By emitting clicks, or short pulses of sound, marine mammals can listen for echoes and detect objects underwater. Echolocation can be used to locate prey, navigate and avoid obstacles in low-visibility environments.