Underwater war «Sonar» Definition, Types, Uses & Tasks

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During World War II‭, ‬one of the greatest dangers faced by the Allies was the attacks of German submarines against Allied ships along the Atlantic supply lines‭, ‬which was one of the greatest dangers faced by the Allied forces‭.‬

To counter this threat‭, ‬the British Royal Navy and the United States Navy utilized two types of underwater detection equipment‭, ‬which provided a new way to detect and attack submarines submerged underwater‭, ‬despite their limited effectiveness‭.‬

Those two types were‭ “‬ASDIC‭” ‬and‭ “‬Sonar‭”. ‬Research and development continued on the two technologies in Britain and the United States and as soon as World War II broke out‭, ‬the Royal Navy had 220‭ ‬warships including destroyers and patrol ships equipped with‭ “‬ASDIC‭” ‬devices‭, ‬while the United States Navy entered the war in December 1941‭, ‬with 170‭ ‬destroyers equipped with‭ “‬Sonar‭” ‬devices‭. ‬These foundations led to great progress‭, ‬especially in the field of electronics‭, ‬paving the way for the development of more‭ ‬accurate equipment‭.‬

The purpose of this research is to explain the principles of sonar operation‭, ‬look at its role‭, ‬and the types of available devices‭.‬

Sound dispersion

Sound waves are pressure waves that move through a medium‭, ‬that may be solid‭, ‬liquid‭, ‬or gas‭. ‬Sound waves do not propagate in a‭ ‬vacuum‭, ‬and the source of the sound waves is a transducer‭, ‬equipped with an oscillating barrier‭ (‬similar to the ones found in speakers‭).‬

Sonar devices usually use frequencies in the range of sound frequencies between 4‭ ‬and 14‭ ‬kHz‭.  ‬In water‭, ‬the speed of sound is 4‭ ‬times its speed in the air‭, ‬and it ranges from 1460‭ ‬meters per second at a temperature of 4‭ ‬degrees Celsius to 1620‭ ‬meters at a‭ ‬temperature of 30‭ ‬degrees Celsius‭. ‬

When a sound wave hits an object within the medium in which it is traveling‭, ‬or the boundary between two mediums‭ (‬such as water‭ ‬and air‭), ‬this causes a reflection in the wave‭, ‬and it bounces off the object it hits at an angle equal to the angle of incidence while at sea‭, ‬up to a depth of 200‭ ‬meters‭, ‬the waves are reflected after hitting the bottom‭.‬

While using sonar‭, ‬we encounter 3‭ ‬types of echoes‭: ‬body-reflected sounds‭, ‬surface-reflected sounds‭ (‬which have the highest intensity immediately after being transmitted‭), ‬and bottom-reflected sounds‭ (‬which are most intense in shallow water‭, ‬especially in the presence of a rocky bottom‭.)‬

Another important factor in using sonar is the loss of energy to sound waves as they pass through the medium‭ (‬in the case of seawater‭). ‬The acuity of this energy loss depends on the range of the device‭, ‬and depends on the state of the sea‭, ‬and is usually high if the water has air bubbles‭ (‬as in the case of a ship sailing‭, ‬or the presence of strong surface winds that form surface foam from air and seawater‭).‬

Energy absorption or dispersion occurs if there are floating or suspended particles‭, ‬such as seaweed‭, ‬or parasites that live in‭ ‬water‭.‬

Among all the related factors rarefaction is the most important element in the transmission of sound‭, ‬as it can reduce the range‭ ‬in which any submarine can be detected to almost zero‭, ‬or make it change unexpectedly‭, ‬depending on the conditions of the sea‭.‬

Submarines usually try to make the most of the effects of disruption during offensive actions‭.‬

Depth noise

Sonar devices are usually equipped with listening devices‭, ‬and sometimes the operator of these devices has to rely on his ears to distinguish between different sounds‭. ‬His main task is to capture and verify real signals and distinguish them from depth noise‭.‬

Hearing aids are more useful on submarines than on surface ships‭, ‬as surface ships moving at high speed generate a large amount‭ ‬of noise that overshadows sounds from outside sources‭.‬

The Doppler phenomenon

Austrian physicist Christian Doppler discovered the Doppler principle‭, ‬which can be applied to all wave motion‭, ‬that principle states that if there is a relative movement between the source of the wave and its receiver‭, ‬the apparent frequency in the receiver differs from the frequency in the source‭, ‬and this principle has important practical applications in the use of sonar technology‭.‬

The audible sound frequency is affected by the relative movement between the target and the receiver‭, ‬i.e‭. ‬if the target is moving towards the transducer‭, ‬the echo frequency becomes greater than the frequency known as the Up-Doppler‭, ‬while the resonance frequency becomes lower than the frequency‭, ‬If the target moves away from the transducer‭, ‬which is known as Down-Doppler‭.‬

It is also critical to understand that the Doppler phenomenon is also caused by the movement of the ship‭, ‬and if the target is stationary‭, ‬and the tracked ship is moving‭, ‬the same rule applies‭.‬

Power Transformer Principles

It is the transducer that transmits the impulses to the outside‭. ‬It receives the reverberations‭, ‬making it the heart of modern‭ “‬sonar‭” ‬systems‭.‬

The transducer acts as a receiver for the returning lights‭, ‬similar to a how normal microphone works‭, ‬and as soon as the echo hits the barrier‭, ‬the lengths of the nickel tubes change‭, ‬this leads to the occurrence of a current in the coils surrounding the tubes‭, ‬as a result of the reflection of the transmissions‭, ‬this electrical current produced is used in the receiver‭, ‬after it is‭ ‬amplified and passed on to a display device‭, ‬or converted into audio frequencies in a loudspeaker‭.‬

Practical use of sonar

for many purposes‭, ‬not all of which are related to anti-submarine warfare‭, ‬Naval forces are interested in locating underwater objects‭, ‬most important of which is anti-submarine operations‭. ‬Whatever the goal‭, ‬the success in locating underwater objects is a‭ ‬result of accurate‭, ‬organized‭, ‬and continuous procedures‭, ‬this depends on the fact that the sonar can perform the following operations‭:‬

1‭- Finding contact with the target using sound energy‭.‬

2‭- Maintaining contact until the goal is achieved‭.‬

3‭- Taking an appropriate position from the target‭, ‬with regard to distance and deviation‭.‬

4‭- Determining the speed in relation to the difference in the distance and deviation from the target‭.‬

To explain how these factors come into play‭, ‬we will limit our discussion to the uses of‭ “‬sonar‭” ‬techniques in searches carried‭ ‬out by surface ships designated to work against submarines and the tasks that can be assigned to a surface ship working against‭ ‬a submarine‭ ‬

These tasks include the following‭:‬

The hunt‭:‬‭ ‬detecting the presence of the largest possible number of enemy submarines‭, ‬without any additional information about their exact‭ ‬number or location‭.‬

Identification‭:‬‭ ‬detecting an enemy submarine and locating it with a reasonable degree of accuracy‭.‬

Cover‭:‬‭ ‬finding an area close to friendly naval forces‭, ‬that any enemy submarine must pass through if it wants to attack‭, ‬and then locating any enemy submarine that passes through this well-traveled area‭.‬

The barrier‭:‬‭ ‬the establishment of a fixed barrier to prevent the passage of enemy submarines‭.‬

Types of sonar

Sonar devices can be divided into two main types‭:‬

Directional sonar‭: ‬Directional sonars are still used in port defense‭, ‬as the area that needs to be covered is limited‭, ‬however‭, ‬this type of device‭ ‬has disappeared from modern ships‭. ‬

This type of Sonar devices uses directional transducers to focus the sound pulse that is emitted into a narrow beam‭, ‬and the angle of the target is determined by pointing the transducer to receive the maximum force of the echo‭.  ‬The echo-response is audible‭, ‬beginning a slow‭, ‬step-by-step thorough underwater inspection process‭.‬

Scanning Sonar‭: ‬This type of sonar solved many of the issues that were caused by the long time required to search a large area‭, ‬as the scanning‭ ‬sonar allows the operator to inspect the area around his ship in a very short time‭, ‬a feature that was unavailable in the past‭.‬

‭ ‬Thus‭, ‬it is now possible to inspect a circular area with a diameter of 1000‭ ‬yards in 1.5‭ ‬seconds‭, ‬while the directional sonar requires 60‭ ‬times as long to inspect the same area‭.  ‬Scanning sonar also allows the operator to track all underwater objects within the range of his device‭, ‬providing a complete and continuous picture of all objects and sound sources in the area‭, ‬and he can‭ ‬track several different targets simultaneously‭.‬

Types of sonar scanning devices

There are two main types of scanning sonars‭, ‬the first emits short sound pulses‭, ‬while the second transmits a continuous signal‭ ‬of a different frequency‭.‬

Airborne sonar devices

Searching for submarines using aircrafts is an important factor in anti-submarine warfare‭.‬

‭ ‬All types of anti-submarine aircraft‭, ‬whether fixed-wing or helicopters‭, ‬can carry out missions to search for and attack submarines‭, ‬taking advantage of many qualities that are not available in ships‭, ‬such as speed‭, ‬maneuverability‭ (‬especially for helicopters‭), ‬and speed of intervention‭, ‬in addition‭, ‬the plane does not emit any sound that could interfere with the processes of‭ “‬sonar‭”, ‬since it does not come into contact with water‭.‬

Detection devices used on aircraft are very different from those used on ships‭, ‬some of which‭ (‬such as MAD devices‭) ‬play a crucial role in achieving what is known as‭ “‬discrete coverage‭”, ‬which is useful in giving a general idea of‭ ‬​​the different types of devices‭, ‬namely‭: ‬diving‭ “‬sonars‭”, ‬sound buoys‭, ‬magnetic anomaly phenomenon detectors‭ (‬MAD‭), ‬and advanced‭ ‬sonar‭.‬

Diving sonar

Hydrophones or transducers are attached to the end of a wire that connects to a helicopter’s‭ “‬sonar‭”, ‬then the hydrophone is lowered into the sea‭, ‬and the onboard operator begins to listen‭.‬

This type of equipment can only be used in helicopters‭, ‬because Helicopters‭, ‬while very noisy in the air‭, ‬make very little sound‭ ‬underwater‭, ‬so they are safe from the countermeasures deployed by submarines‭.‬

Once an enemy submarine is detected‭, ‬the helicopter can either call for a hunter destroyer‭, ‬or an anti-submarine ship‭, ‬to attack‭ ‬the target or attack it by itself if it is carrying guided torpedoes such as the American‭ “‬Mark 43‭” ‬torpedo‭.‬

Magnetic phenomenon detector

The Magnetic Phenomenon Anomaly Detector‭ (‬MAD‭) ‬is another very important device in detecting submarines‭, ‬and it can be fitted to‭ ‬fixed-wing aircrafts or helicopters‭. ‬The MAD device enables the crew of a low-flying patrol aircraft to detect the presence of‭ ‬submarines‭.‬

Sound buoys

Sound buoys are used to detect underwater sounds‭,  ‬transmitted by radio to nearby aircraft‭, ‬or other stations equipped with the‭ ‬appropriate receiving equipment‭.‬

Sound buoys are single-use devices that are ejected from any type of aircraft‭, ‬using a small parachute carried by the device‭.‬

To track the enemy submarine‭, ‬several buoys must be deployed‭, ‬according to a pre-prepared pattern or design‭. ‬Each water speaker‭ ‬is connected to a long wire that is loosened to the fullest‭, ‬leaving the water speaker underwater and attached to the buoy that‭ ‬remains on the surface‭, ‬then a comparison between the signals picked up by several water buoys enables the aircraft to determine‭ ‬the location of the target‭.‬

Port Defense

One of the main goals of anti-submarine warfare is to prevent submarines from approaching or entering ports‭, ‬thus defense forces‭ ‬establish complete detection lines‭, ‬using various types of devices‭.‬

These types include a multi-indicator instrument and a magnetic frame indicator that is placed on the seafloor to record any distortion in the Earth’s magnetic field‭, ‬which may be caused by the presence of a metal object moving over it‭.‬

Other acoustic devices record the sounds of the propellers and motors‭, ‬alerting operators to the approach of any ship‭. ‬In addition‭, ‬the submerged part of the hulls of ships‭ – ‬not just submarines‭ –  ‬forms a surface that reflects sound waves‭, ‬and so‭ “‬sonar‭” ‬devices can be used against them as well‭.‬

In addition to all of the previously mentioned devices‭, ‬there is a device known as the‭ “‬Herald‭”, ‬used to defend ports‭. ‬

Tactically speaking‭, ‬the Herald is the most accurate underwater sound detector‭, ‬as it allows the operator to determine the exact‭ ‬direction and range of the potential target‭, ‬so that the patrol ships guarding can head to the exact location of the target‭.‬

Crucial conclusion

Today‭, ‬Anti-submarine warfare is of particular importance‭, ‬as the Russian submarine fleet has become the greatest threat to the‭ ‬western lines of communication in the Atlantic in recent years‭, ‬other reasons stem from the development of the submarine fleets‭ ‬carrying American and Russian ballistic missiles‭.‬

submarines carrying nuclear missiles are considered one of the two countries‭’ ‬biggest nuclear deterrents‭, ‬given the high mobility of this type of weapon‭, ‬and the difficulty of locating the submarine carrying it‭, ‬it can survive most surprise attacks that would paralyze the movement of the air force and naval missile silos‭.‬

It has become quite clear that the ability to determine the locations of nuclear submarines will put either country in a position of power to turn the‭ “‬balance of terror‭” ‬and carry out a surprise attack‭, ‬without fear of any retaliation‭, ‬and thus special attention is given to research and development of anti-submarine warfare‭, ‬and Submarine detection equipment‭. ‬

There is no doubt that in the future we will witness major developments in this field‭, ‬which will have an effective impact on anti-submarine warfare and maritime strategy in general‭.‬

‮«‬‭ ‬By‭: ‬Dr‭. ‬Moeen Ahmed Mahmoud‭ (‬military researcher and strategist‭)‬

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