Editing Sonar (section)

== History ==
Although some animals ([[dolphin]]s, [[bat]]s, some [[shrew]]s, and others) have used sound for communication and object detection for millions of years, use by humans in the water was initially recorded by Leonardo da Vinci in 1490: a tube inserted into the water was said to be used to detect vessels by placing an ear to the tube.<ref name="DaVinci">{{cite book|last=Fahy|first=Frank|others=John Gerard Walker|title=Fundamentals of noise and vibration|publisher=Taylor & Francis|year=1998|pages=375|isbn=978-0-419-24180-5}}</ref>

In the late 19th century, an [[Submarine signals|underwater bell]] was used as an ancillary to [[lighthouse]]s or [[Lightvessel|lightships]] to provide warning of hazards.<ref>Thomas Neighbors, David Bradley (ed.), ''Applied Underwater Acoustics: Leif Bjørnø'', Elsevier, 2017, {{ISBN|0128112476}}, page 8</ref>

The use of sound to "echo-locate" underwater in the same way as bats use sound for aerial navigation seems to have been prompted by the {{RMS|Titanic||2}} disaster of 1912.<ref>M. A. Ainslie (2010), ''Principles of Sonar Performance Modeling'', Springer, p. 10</ref> The world's first [[patent]] for an underwater echo-ranging device was filed at the British [[UK Intellectual Property Office|Patent Office]] by English meteorologist [[Lewis Fry Richardson]] a month after the sinking of ''Titanic'',<ref name="hilrob">{{cite book|last=Hill|first=M. N.|others=Allan R. Robinson|title=Physical Oceanography|publisher=Harvard University Press|year=1962|pages=498}}</ref> and a German physicist [[Alexander Behm]] obtained a patent for an echo sounder in 1913.<ref>W. Hackmann (1984), ''Seek and Strike'', pn</ref>

The Canadian engineer [[Reginald Fessenden]], while working for the Submarine Signal Company in [[Boston]], Massachusetts, built an experimental system beginning in 1912, a system later tested in Boston Harbor, and finally in 1914 from the U.S. Revenue Cutter ''Miami'' on the [[Grand Banks]] off [[Newfoundland (island)|Newfoundland]].<ref name="hilrob"/><ref>{{cite book|last=Seitz|first=Frederick|title=The cosmic inventor: Reginald Aubrey Fessenden (1866–1932)|publisher=American Philosophical Society|year=1999|volume=89|pages=41–46|isbn=978-0-87169-896-4}}</ref> In that test, Fessenden demonstrated depth sounding, underwater communications ([[Morse code]]) and echo ranging (detecting an iceberg at a {{convert|2|mi|km|adj=on}} range).<ref>{{cite journal |last=Hendrick |first=Burton J. |date=August 1914 |title=Wireless under the water: a remarkable device that enables a ship's captain to determine the exact location of another ship even en the densest fog |journal=[[World's Work|The World's Work: A History of Our Time]] |volume=XLIV |issue=2 |pages=431–434  |url=https://books.google.com/books?id=zegeQtMn9JsC&pg=PA431 |access-date=2009-08-04 }}</ref><ref>{{Cite journal | title = Report of Captain J. H. Quinan of the U.S.R.C. Miami on the echo fringe method of detecting icebergs and taking continuous soundings | journal = Hydrographic Office Bulletin | date = 1914-05-13 }} (quoted in [http://oceanexplorer.noaa.gov/library/readings/subsignaling/subsignaling.html a NOAA transcript by Central Library staff April, 2002] {{webarchive|url=https://web.archive.org/web/20100510134752/http://oceanexplorer.noaa.gov/library/readings/subsignaling/subsignaling.html |date=2010-05-10 }}.</ref> The "[[Fessenden oscillator]]", operated at about 500&nbsp;Hz frequency, was unable to determine the bearing of the iceberg due to the 3-metre wavelength and the small dimension of the transducer's radiating face (less than {{frac|1|3}} wavelength in diameter). The ten [[Montreal]]-built [[British H-class submarine]]s launched in 1915 were equipped with Fessenden oscillators.<ref>{{cite web |url=http://www.gwpda.org/naval/hbowcap.htm|title=The rotary bowcap |url-status=live |archive-url=https://web.archive.org/web/20070626182639/http://www.gwpda.org/naval/hbowcap.htm |archive-date=2007-06-26 }}</ref>

During [[World War I]] the need to detect [[submarine]]s prompted more research into the use of sound. The British made early use of underwater listening devices called [[hydrophones]], while the French physicist [[Paul Langevin]], working with a Russian immigrant electrical engineer Constantin Chilowsky, worked on the development of active sound devices for detecting submarines in 1915. Although [[piezoelectricity|piezoelectric]] and [[Magnetostriction|magnetostrictive]] transducers later superseded the [[electrostatics|electrostatic]] transducers they used, this work influenced future designs. Lightweight sound-sensitive plastic film and fibre optics have been used for hydrophones, while [[Terfenol-D]] and [[lead magnesium niobate]] (PMN) have been developed for projectors.

=== ASDIC ===
[[File:ASDIC.png|thumb|right|ASDIC display unit from around 1944]]
In 1916, under the British [[Board of Invention and Research]], Canadian physicist [[Robert William Boyle]] took on the active sound detection project with [[Albert Beaumont Wood|A. B. Wood]], producing a prototype for testing in mid-1917. This work for the Anti-Submarine Division of the British Naval Staff was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy, no mention of sound experimentation or quartz was made – the word used to describe the early work ("supersonics") was changed to "ASD"ics, and the quartz material to {{not a typo|"ASD"ivite}}: "ASD" for "Anti-Submarine Division", hence the British acronym ''ASDIC''. In 1939, in response to a question from the ''[[Oxford English Dictionary]]'', the [[British Admiralty|Admiralty]] made up the story that it stood for "Allied Submarine Detection Investigation Committee", and this is still widely believed,<ref name="Abbot">{{cite web |url=http://abbot.us/DD629/dictionary/ |title=World War II Naval Dictionary |website=USS Abbot (DD-629) |access-date=12 November 2019 |archive-date=12 December 2013 |archive-url=https://web.archive.org/web/20131212091457/http://abbot.us/DD629/dictionary/ |url-status=dead }}</ref> though no committee bearing this name has been found in the Admiralty archives.<ref name="Hackmann">W. Hackmann, ''Seek & Strike: Sonar, anti-submarine warfare and the Royal Navy 1914–54'' (HMSO, London, 1984).</ref>

By 1918, Britain and France had built prototype active systems. The British tested their ASDIC on {{HMS|Antrim|1903|6}} in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school [[RNAS Portland (HMS Osprey)|HMS ''Osprey'']] and a training [[flotilla]] of four vessels were established on [[Isle of Portland|Portland]] in 1924.

By the outbreak of [[World War II]], the [[Royal Navy]] had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine system. The effectiveness of early ASDIC was hampered by the use of the [[depth charge]] as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in the moments leading up to attack. The hunter was effectively firing blind, during which time a submarine commander could take evasive action. This situation was remedied with new tactics and new weapons.

The tactical improvements developed by [[Frederic John Walker]] included the creeping attack. Two anti-submarine ships were needed for this (usually sloops or corvettes). The "directing ship" tracked the target submarine on ASDIC from a position about 1500 to 2000 yards behind the submarine. The second ship, with her ASDIC turned off and running at 5 knots, started an attack from a position between the directing ship and the target. This attack was controlled by radio telephone from the directing ship, based on their ASDIC and the range (by rangefinder) and bearing of the attacking ship. As soon as the depth charges had been released, the attacking ship left the immediate area at full speed. The directing ship then entered the target area and also released a pattern of depth charges. The low speed of the approach meant the submarine could not predict when depth charges were going to be released. Any evasive action was detected by the directing ship and steering orders to the attacking ship given accordingly. The low speed of the attack had the advantage that the [[G7es torpedo|German acoustic torpedo]] was not effective against a warship travelling so slowly. A variation of the creeping attack was the "plaster" attack, in which three attacking ships working in a close line abreast were directed over the target by the directing ship.<ref name="Burn">{{cite book |last1=Burn |first1=Alan |title=The Fighting Captain: Frederic John Walker RN and the Battle of the Atlantic |date=1993 |publisher=Pen and Sword |location=Barnsley |isbn=978-1-84415-439-5 |edition=2006, Kindle|chapter=Appendix 6}}</ref>

The new weapons to deal with the ASDIC blind spot were "ahead-throwing weapons", such as [[Hedgehog (weapon)|Hedgehogs]] and later [[Squid (weapon)|Squids]], which projected warheads at a target ahead of the attacker and still in ASDIC contact. These allowed a single escort to make better aimed attacks on submarines. Developments during the war resulted in British ASDIC sets that used several different shapes of beam, continuously covering blind spots. Later, [[acoustic torpedo]]es were used.

Early in World War II (September 1940), British ASDIC technology was [[Tizard Mission|transferred for free]] to the United States. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed. These included [[sonobuoy]]s, first developed by the British in 1944 under the [[codename]] ''High Tea'', dipping/dunking sonar and [[naval mine|mine]]-detection sonar. This work formed the basis for post-war developments related to countering the [[nuclear submarine]].

=== SONAR ===
During the 1930s American engineers developed their own underwater sound-detection technology, and important discoveries were made, such as the existence of [[thermocline]]s and their effects on sound waves.<ref>{{cite book |url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112064674325;view=1up;seq=503 |title=Howeth: Chapter XXXIX |date=1963 |publisher=Washington}}</ref> Americans began to use the term ''SONAR'' for their systems, coined by [[Frederick Vinton Hunt|Frederick Hunt]] to be the equivalent of [[Radar|RADAR]].<ref name="AIP oral history part II">{{cite web|title=AIP Oral History: Frederick Vinton Hunt, Part II|date=23 February 2015|url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4688-2}}</ref>

=== US Navy Underwater Sound Laboratory ===
In 1917, the US Navy acquired [[J. Warren Horton]]'s services for the first time. On leave from [[Bell Labs]], he served the government as a technical expert, first at the experimental station at [[Nahant, Massachusetts]], and later at US Naval Headquarters, in [[London]], England. At Nahant he applied the newly developed [[vacuum tube]], then associated with the formative stages of the field of applied science now known as [[electronics]], to the detection of underwater signals. As a result, the [[carbon microphone|carbon button microphone]], which had been used in earlier detection equipment, was replaced by the precursor of the modern [[hydrophone]]. Also during this period, he experimented with methods for towing detection. This was due to the increased sensitivity of his device. The principles are still used in modern [[Towed array sonar|towed sonar]] systems.

To meet the defense needs of Great Britain, he was sent to England to install in the [[Irish Sea]] bottom-mounted hydrophones connected to a shore listening post by submarine cable. While this equipment was being loaded on the cable-laying vessel, World War I ended and Horton returned home.

During World War II, he continued to develop sonar systems that could detect submarines, mines, and torpedoes. He published ''Fundamentals of Sonar'' in 1957 as chief research consultant at the [[Underwater Sound Laboratory|US Navy Underwater Sound Laboratory]]. He held this position until 1959 when he became technical director, a position he held until mandatory retirement in 1963.<ref>from Dr. Horton's autobiographical sketch and US Department of the Navy Undersea Warfare Center</ref><ref>{{cite book|last=Horton|first=J. Warren|title=Fundamentals of Sonar| publisher=U. S. Naval Institute, Annapolis, MD.|year=1957|pages=387}}</ref>

=== Materials and designs in the US and Japan ===
There was little progress in US sonar from 1915 to 1940. In 1940, US sonars typically consisted of a [[magnetostrictive]] transducer and an array of nickel tubes connected to a 1-foot-diameter steel plate attached back-to-back to a [[Rochelle salt]] crystal in a spherical housing. This assembly penetrated the ship hull and was manually rotated to the desired angle. The [[piezoelectric]] Rochelle salt crystal had better parameters, but the magnetostrictive unit was much more reliable. High losses to US merchant supply shipping early in World War II led to large scale high priority US research in the field, pursuing both improvements in magnetostrictive transducer parameters and Rochelle salt reliability. [[Ammonium dihydrogen phosphate]] (ADP), a superior alternative, was found as a replacement for Rochelle salt; the first application was a replacement of the 24&nbsp;kHz Rochelle-salt transducers. Within nine months, Rochelle salt was obsolete. The ADP manufacturing facility grew from few dozen personnel in early 1940 to several thousands in 1942.

One of the earliest application of ADP crystals were hydrophones for [[acoustic mine]]s; the crystals were specified for low-frequency cutoff at 5&nbsp;Hz, withstanding mechanical shock for deployment from aircraft from {{convert|10000|ft|m|abbr=on|order=flip}}, and ability to survive neighbouring mine explosions. One of key features of ADP reliability is its zero aging characteristics; the crystal keeps its parameters even over prolonged storage.

Another application was for acoustic homing torpedoes. Two pairs of directional hydrophones were mounted on the torpedo nose, in the horizontal and vertical plane; the difference signals from the pairs were used to steer the torpedo left-right and up-down. A countermeasure was developed: the targeted submarine discharged an [[effervescent]] chemical, and the torpedo went after the noisier fizzy decoy. The counter-countermeasure was a torpedo with active sonar – a transducer was added to the torpedo nose, and the microphones were listening for its reflected periodic tone bursts. The transducers comprised identical rectangular crystal plates arranged to diamond-shaped areas in staggered rows.

Passive sonar arrays for submarines were developed from ADP crystals. Several crystal assemblies were arranged in a steel tube, vacuum-filled with [[castor oil]], and sealed. The tubes then were mounted in parallel arrays.

The standard US Navy scanning sonar at the end of World War II operated at 18&nbsp;kHz, using an array of ADP crystals. Desired longer range, however, required use of lower frequencies. The required dimensions were too big for ADP crystals, so in the early 1950s magnetostrictive and [[barium titanate]] piezoelectric systems were developed, but these had problems achieving uniform impedance characteristics, and the beam pattern suffered. Barium titanate was then replaced with more stable [[lead zirconate titanate]] (PZT), and the frequency was lowered to 5&nbsp;kHz. The US fleet used this material in the AN/SQS-23 sonar for several decades. The SQS-23 sonar first used magnetostrictive nickel transducers, but these weighed several tons, and nickel was expensive and considered a critical material; piezoelectric transducers were therefore substituted. The sonar was a large array of 432 individual transducers. At first, the transducers were unreliable, showing mechanical and electrical failures and deteriorating soon after installation; they were also produced by several vendors, had different designs, and their characteristics were different enough to impair the array's performance. The policy to allow repair of individual transducers was then sacrificed, and "expendable modular design", sealed non-repairable modules, was chosen instead, eliminating the problem with seals and other extraneous mechanical parts.<!-- split this off to SQS-23 article? --><ref>Frank Massa. [http://www.massa.com/wp-content/uploads/Frank_Massa-Sonar_Transducers-A_History.pdf Sonar Transducers: A History] {{webarchive|url=https://web.archive.org/web/20150418081805/http://www.massa.com/wp-content/uploads/Frank_Massa-Sonar_Transducers-A_History.pdf |date=2015-04-18 }}</ref>

The [[Imperial Japanese Navy]] at the onset of World War II used projectors based on [[quartz]]. These were big and heavy, especially if designed for lower frequencies; the one for Type 91 set, operating at 9&nbsp;kHz, had a diameter of {{convert|30|in}} and was driven by an oscillator with 5&nbsp;kW power and 7&nbsp;kV of output amplitude. The Type 93 projectors consisted of solid sandwiches of quartz, assembled into spherical [[cast iron]] bodies. The Type 93 sonars were later replaced with Type 3, which followed German design and used magnetostrictive projectors; the projectors consisted of two rectangular identical independent units in a cast-iron rectangular body about {{convert|16|x|9|in}}. The exposed area was half the wavelength wide and three wavelengths high. The magnetostrictive cores were made from 4&nbsp;mm stampings of nickel, and later of an [[Alperm|iron-aluminium alloy]] with aluminium content between 12.7% and 12.9%. The power was provided from a 2&nbsp;kW at 3.8&nbsp;kV, with polarization from a 20&nbsp;V, 8&nbsp;A DC source.

The passive hydrophones of the Imperial Japanese Navy were based on moving-coil design, Rochelle salt piezo transducers, and [[carbon microphone]]s.<ref name="USNTMJ-200B-0343-0412">{{cite web |url=http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200B-0343-0412%20Report%20E-10.pdf |title=Japanese Sonar and Asdic |access-date=2015-05-08 |url-status=dead |archive-url=https://web.archive.org/web/20150924013502/http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200B-0343-0412%20Report%20E-10.pdf |archive-date=2015-09-24 }}</ref>

=== Later developments in transducers ===
Magnetostrictive transducers were pursued after World War II as an alternative to piezoelectric ones. Nickel scroll-wound ring transducers were used for high-power low-frequency operations, with size up to {{convert|13|ft}} in diameter, probably the largest individual sonar transducers ever. The advantage of metals is their high tensile strength and low input electrical impedance, but they have electrical losses and lower coupling coefficient than PZT, whose tensile strength can be increased by [[prestressing]]. Other materials were also tried; nonmetallic [[Ferrite (magnet)|ferrites]] were promising for their low electrical conductivity resulting in low [[eddy current]] losses, [[Metglas]] offered high coupling coefficient, but they were inferior to PZT overall. In the 1970s, compounds of [[rare earths]] and iron were discovered with superior magnetomechanic properties, namely the [[Terfenol-D]] alloy. This made possible new designs, e.g. a hybrid magnetostrictive-piezoelectric transducer. The most recent of these improved magnetostrictive materials is [[Galfenol]].

Other types of transducers include variable-reluctance (or moving-armature, or electromagnetic) transducers, where magnetic force acts on the surfaces of gaps, and moving coil (or electrodynamic) transducers, similar to conventional speakers; the latter are used in underwater sound calibration, due to their very low resonance frequencies and flat broadband characteristics above them.<ref>{{Cite journal |url=https://books.google.com/books?id=srREi-ScbFcC&pg=PA45 |title=Transducers and Arrays for Underwater Sound |journal=[[The Journal of the Acoustical Society of America]] |volume=124 |issue=3 |pages=1385 |url-status=live |archive-url=https://web.archive.org/web/20180426001103/https://books.google.com/books?id=srREi-ScbFcC&pg=PA45 |archive-date=2018-04-26 |bibcode=2008ASAJ..124.1385S |last1=Sherman |first1=Charles H |last2=Butler |first2=John L |last3=Brown |first3=David A |year=2008 |doi=10.1121/1.2956476 |isbn=9780387331393|doi-access=free }}</ref>