Sonar

**Sonar** (**so**und **na**vigation **r**anging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.

## Overview

Although some animals (dolphins, bats, some shrews, and others) have used sound for communication and object detection for millions of years, the first recorded use by humans is done by the Italian scientist Leonardo da Vinci in 1490 back on Earth who used a tube inserted into the water to detect vessels by ear. It was developed during World War I to counter the growing threat of submarine warfare, with an operational passive sonar system in use by 1918. Modern active sonar systems use an acoustic transponder to generate a sound wave which is reflected back from target objects.

## Types

### Active Sonar

Active sonar uses a sound transmitter and a receiver. When the two are in the same place it is monostatic operation. When the transmitter and receiver are separated it is bistatic operation. When more transmitters (or more receivers) are used, again spatially separated, it is multistatic operation. Most sonars are used monostatically with the same array often being used for transmission and reception. Active sonobuoy fields may be operated multistatically.

### Passive Sonar

Passive sonar listens without transmitting. It is often employed in military settings, although it is also used in science applications, *e.g.*, detecting fish for presence/absence studies in various aquatic environments.

## Countermeasures

Like radar, there are methods in order to avoid detection by sonar. Sound travels better underwater than in air, and modern submariners employ the tactic of 'running silent.' In other words, they try not to make any noise. This can include shutting down the engines and other loud machinery, and the crew not moving or talking. Due to the sensitivity of the sonar, a slight sound can give away their position. Furthermore, there is no way to suppress the sound of a torpedo after it leaves the submarine, so the submarine must immediately move from its launch point.

Over the years, submarine technology has advanced to developing sound-suppression equipment. Submarine hulls are now coated with sound-absorbing material so they don't appear on active and passive sonar systems. It also keeps sound from inside the submarine from leaking out.

Another way to avoid detection is to deceive the sonar system by using a decoy. This is a drone torpedo that emits a signal similar to that of a full-size sub. As a result, the enemy is tricked into tracking the decoy while the actual submarine either escapes or counterattacks.

## Service History

### Japan

Japan uses both active and passive types of sonar even before its transfer to the New World. See Skirmish at New Japan Sea for details. Their submarines are also equipped with a sound-suppression hull and decoys. Their crews are all well-trained in 'running silent' methods.

### Gra Valkas Empire

The Gra Valkas Empire also uses two types of sonar. However initially, they uses only passive sonar. The captain of the Cetus-class Submarine *"Mira"* commented that Japan is using a technology (active sonar) that is still in development in the empire. See Skirmish at New Japan Sea for details. Gra Valkan submarine crews have no concept of 'running silent' and their submarines are loud and noisy. The JMSDF were baffled over how easily they could detect the Gra Valkan submarines and how it went against the common logic of submarine warfare.

The use of active sonar in GVE was just recently featured during the Great Naval Battle of Japan where the 2nd Advanced Fleet is trying to locate the Soryu-class Submarine of the JMSDF. However their efforts are futile as the JMSDF is equipped with far more sophisticated submarines tactics and technology, which resulted in the destruction of the Great Fleet's 2nd Advanced Fleet.