Editing Sonar (section)

===Ocean surveillance===
The United States began a system of passive, fixed ocean surveillance systems in 1950 with the classified name [[SOSUS|Sound Surveillance System (SOSUS)]] with [[American Telephone and Telegraph Company]] (AT&T), with its [[Bell Laboratories]] research and [[Western Electric]] manufacturing entities being contracted for development and installation. The systems exploited the [[SOFAR channel]], also known as the deep sound channel, where a sound speed minimum creates a [[waveguide]] in which low frequency sound travels thousands of miles. Analysis was based on an AT&T sound spectrograph, which converted sound into a visual [[spectrogram]] representing a [[time–frequency analysis]] of sound that was developed for speech analysis and modified to analyze low-frequency underwater sounds. That process was [[Low Frequency Analyzer and Recorder (LOFAR)|Low Frequency Analysis and Recording]] and the equipment was termed the Low Frequency Analyzer and Recorder, both with the acronym LOFAR. LOFAR research was termed ''Jezebel'' and led to usage in air and surface systems, particularly sonobuoys using the process and sometimes using "Jezebel" in their name.<ref name=Whitman>{{cite magazine |last=Whitman |first=Edward C. |date=Winter 2005 |title=SOSUS The "Secret Weapon" of Undersea Surveillance |magazine=Undersea Warfare |volume=7 |issue=2 |url=https://www.public.navy.mil/subfor/underseawarfaremagazine/Issues/Archives/issue_25/sosus.htm |access-date=5 January 2020 |archive-date=24 March 2020 |archive-url=https://web.archive.org/web/20200324114806/https://www.public.navy.mil/subfor/underseawarfaremagazine/Issues/Archives/issue_25/sosus.htm |url-status=dead }}</ref><ref name=ICAA>{{cite web |title=Integrated Undersea Surveillance System (IUSS) History 1950 - 2010 |publisher=IUSS/CAESAR Alumni Association |url=http://www.iusscaa.org/history.htm |access-date=22 May 2020}}</ref><ref>{{cite journal |last1=Munk |first1=Walter H. |last2=Spindel |first2=Robert C. |last3=Baggeroer |first3=Arthur |last4=Birdsall |first4=Theodore G. |date=20 May 1994  |journal=Journal of the Acoustical Society of America |title=The Heard Island Feasibility Test |volume=96  |issue=4 |pages=2330–2342 |publisher=Acoustical Society of America |doi=10.1121/1.410105 |bibcode=1994ASAJ...96.2330M |url=https://docs.google.com/viewer?url=http%3A%2F%2Fbrigus.physics.mun.ca%2F~zedel%2FP6317%2Fpapers%2Fheard_island.pdf |access-date=26 September 2020}}</ref><ref>{{cite book |last1=Lieberman |first1=Philip |last2=Blumstein |first2=Sheila E.  |date= 4 February 1988|title=Speech Physiology, Speech Perception, and Acoustic Phonetics |location=Cambridge, Cambridgeshire, UK/New York |publisher=Cambridge University Press  |isbn=0521308666 |lccn=87013187  |pages=51–52 |url=https://books.google.com/books?id=c07XORQ3NdkC&pg=PA51 |access-date=22 May 2020}}</ref> The proposed system offered such promise of long-range submarine detection that the Navy ordered immediate moves for implementation.<ref name=ICAA/><ref name=CUS>{{cite web |title=Origins of SOSUS |publisher=Commander, Undersea Surveillance |url=https://www.public.navy.mil/subfor/cus/Pages/sosus_origins.aspx |access-date=22 May 2020 |archive-date=7 August 2020 |archive-url=https://web.archive.org/web/20200807123302/https://www.public.navy.mil/subfor/cus/Pages/sosus_origins.aspx |url-status=dead }}</ref>

[[File:Watch floor.gif|thumb|Lofargram writers, one for each array beam, on a NAVFAC watch floor]]
Between installation of a test array followed by a full scale, forty element, prototype operational array in 1951 and 1958 systems were installed in the Atlantic and then the Pacific under the unclassified name ''Project Caesar''. The original systems were terminated at classified shore stations designated Naval Facility (NAVFAC) explained as engaging in "ocean research" to cover their classified mission. The system was upgraded multiple times with more advanced cable allowing the arrays to be installed in ocean basins and upgraded processing. The shore stations were eliminated in a process of consolidation and rerouting the arrays to central processing centers into the 1990s. In 1985, with new mobile arrays and other systems becoming operational the collective system name was changed to Integrated Undersea Surveillance System (IUSS). In 1991 the mission of the system was declassified. The year before IUSS insignia were authorized for wear. Access was granted to some systems for scientific research.<ref name=Whitman/><ref name=ICAA/>

A similar system is believed to have been operated by the Soviet Union.