Sound Surveillance System (SOSUS) was the original name for a submarine detection system based on passive sonar developed by the United States Navy to track Soviet submarines. The system's true nature was classified with the name and acronym SOSUS classified as well. The unclassified name Project Caesar was used to cover the installation of the system and a cover story developed regarding the shore stations, identified only as a Naval Facility (NAVFAC), being for oceanographic research. The name changed to Integrated Undersea Surveillance System (IUSS) in 1985, as the fixed bottom arrays were supplemented by the mobile Surveillance Towed Array Sensor System (SURTASS) and other new systems. The commands and personnel were covered by the "oceanographic" term until 1991 when the mission was declassified. As a result, the commands, Oceanographic System Atlantic and Oceanographic System Pacific became Undersea Surveillance Atlantic and Undersea Surveillance Pacific, and personnel were able to wear insignia reflecting the mission.
The original system was capable of oceanic surveillance with the long ranges made possible by exploiting the deep sound channel (SOFAR channel). An indication of ranges is the first detection, recognition and reporting of a Soviet nuclear submarine coming into the Atlantic through the Greenland-Iceland-United Kingdom (GIUK) gap by an array terminating at NAVFAC Barbados on 6 July 1962. The linear arrays with hydrophones placed on slopes within the sound channel enabled beamforming processing at the shore facilities to form azimuthal beams. When two or more arrays held a contact, triangulation provided approximate positions for air or surface assets to localize.Before the nature of the arrays became known, many writers assumed SOSUS was a barrier system, rather than arrays giving surveillance of entire ocean basins. An associated program, Colossus, was such a system intended to be installed across straits.
SOSUS grew out of tasking in 1949 to scientists and engineers to study the problem of antisubmarine warfare. It was implemented as a chain of underwater hydrophone arrays linked by cable, based on commercial telephone technology, to shore stations located around the western Atlantic Ocean from Nova Scotia to Barbados. The first experimental array was a six-element test array laid at Eleuthera in the Bahamas in 1951, followed, after successful experiments with a target submarine, in 1952 by a fully-functional , forty-hydrophone array. At that time the order for stations was increased from six to nine. The then-secret 1960 Navy film Watch in the Sea describes the production arrays as being long. In 1954, the order was increased by three more Atlantic stations and an extension into the Pacific, with six stations on the West Coast and one in Hawaii.
In September 1954, Naval Facility Ramey was commissioned in Puerto Rico. Others of the first Atlantic phase followed, and in 1957 the original operational array at Eleuthera got an operational shore facility as the last of the first phase of Atlantic systems. The same year, the Pacific systems began to be installed and activated. Over the next three decades, more systems were added; NAVFAC Keflavik, Iceland in 1966 and NAVFAC Guam in 1968 being examples of expansion beyond the western Atlantic and eastern Pacific. Shore upgrades and new cable technology allowed system consolidation until by 1980 that process had resulted in many closures of the NAVFACs with centralized processing at a new type facility, Naval Ocean Processing Facility (NOPF), that by 1981 saw one for each ocean and mass closing of the NAVFACs.
As the new mobile systems came on line, the original arrays were deactivated and some turned over for scientific research. The surveillance aspect continues with new systems under Commander, Undersea Surveillance.
History SOSUS history began in 1949 when the US Navy approached the Committee for Undersea Warfare, an academic advisory group formed in 1946 under the National Academy of Sciences, to research antisubmarine warfare. As a result, the Navy formed a study group designated Project Hartwell, named for the University of Pennsylvania's G.P. Hartwell who was the Deputy Chairman of the Committee for Undersea Warfare,An alternative story is that it was named for a local bar popular with MIT faculty. under Massachusetts Institute of Technology (MIT) leadership. The Hartwell panel recommended spending of annually to develop systems to counter the Soviet submarine threat consisting primarily of a large fleet of diesel submarines.
That group also recommended a system to monitor low-frequency sound in the SOFAR channel using multiple listening sites equipped with hydrophones and a processing facility that could calculate submarine positions over hundreds of miles.The cited Project HARTWELL report first links arrays with fleet type submarines towing such an array in the GIUK then refers to potential exploitation of the deep sound channel low frequency sounds.
Research As a result of the Hartwell group's recommendations, the Office of Naval Research (ONR) contracted with American Telephone and Telegraph Company (AT&T), with its Bell Laboratories research and Western Electric manufacturing elements, to develop a long range, passive detection system, based on bottom arrays of hydrophones. The system, using equipment termed Low Frequency Analyzer and Recorder and a process termed Low Frequency Analysis and Recording, both with the acronym LOFAR, was to be based on AT&T's sound spectrograph, developed for speech analysis and modified to analyze low-frequency underwater sounds. This research and development effort was given the name Project Jezebel. The origin of the project name was explained by Robert Frosch to Senator Stennis during a 1968 hearing. It was because of the low frequencies, "about the A below middle C on the piano" (about 100–150 cycles) and "Jezebel" being chosen because "she was of low character."This frequency would be approximately A2 on the musical scale, which is two As below middle C
Jezebel and LOFAR branched into the localization of submarines with the AN/SSQ-28 passive omnidirectional Jezebel-LOFAR sonobuoy introduced in 1956 for use by the air antisubmarine forces. That sonobuoy gave the aircraft cued by SOSUS access to the same low frequency and LOFAR capability as SOSUS. Bell Telephone Laboratories time delay correlation was used to fix target position with two or more sonobuoys in a technique named COrrelation Detection And Ranging (CODAR). This, and later specialized, sonobuoys equipped with a small explosive charge could be used in an active mode to detect the echo off the target. The active mode was named by engineers developing the technique "Julie" after a burlesque dancer whose "performance could turn passive buoys active."
Related research, based at Columbia University's Hudson Laboratory, was designated Project Michael. Woods Hole Oceanographic Institution and Scripps Institution of Oceanography were also tasked to develop an understanding of long-range sound transmission under Project Michael. The need to better understand the acoustic environment drove much of the oceanographic research by both the Navy and institutions with Navy funding for oceanography. A major, long-term research program spanning over 25 years, the Long Range Acoustic Propagation Program (LRAPP), made significant progress in such understanding and influenced decisions in SOSUS, significantly the SOSUS expansion into the eastern Atlantic.The sometimes mentioned Sea Spider "system" was simply a complex and unsuccessful experiment with a very large suspended array in the Pacific. It was part of LRAPP as noted on page 181 of the reference. The experiment was part of the Pacific Acoustic Research Kaneohe — Alaska (PARKA) II experiment in 1969. Parts of Sea Spider ended up off Bermuda, designated Testbed for more experiments until that installation also failed. That array was installed by the unusual cable and installation vessel Naubuc. Details of the Sea Spider platform itself may be found in Project Pacific Sea Spider - Technology Used In Developing a Deep-Ocean Ultrastable Platform.
Development and installation The hardware technology was largely that of the commercial telephone system and oil exploration. Cable laying was a capability AT&T and other entities had developed for decades for commercial communications cables. The understanding of the ocean acoustic environment made the system possible rather than development of new technology. SOSUS was a case of new understanding of the environment and then application of largely existing technology and even equipment to the problem.
The forty hydrophones spaced on the array provided the aperture for signal processing to form horizontal azimuthal beams of two to five degrees wide, each beam with a LOFAR analyzer and capability to do narrow-band frequency analysis to discriminate signal from ocean noise and to identify specific frequencies associated with rotating machinery. The NAVFAC watch floor had banks of displays using electrostatic paper, similar to that used for echograms in depth finders.
The product of these displays was the LOFARgram which graphically represented acoustic energy and frequency against time. Those were examined by the personnel trained to identify submarine signatures. When two or more arrays held a target the bearings from each array gave an estimated target position by triangulation. The system could provide cuing information on the presence of the submarines and an approximate location for air or surface antisubmarine warfare assets to localize the target. The first Atlantic stations, ranging from Nova Scotia to Barbados, formed a long line semicircle looking into the Western Atlantic basin with geographic separation for contact correlation and triangulation.
Security The combination of research and engineering under Jezebel and Michael into an actual broad area surveillance system as seen by Project Hartwell's Frederick V. Hunt became the Sound Surveillance System with the acronym SOSUS. Both the full name and acronym were classified. There were occasional slips. A contractor for the Office of Naval Research, Fleet Analysis and Support Division published an unclassified report with "SOSUS" in association with the system acronym "SOSS", defined as "Sound Search Station", and a capability to display data from sonobuoys side by side on either aircraft or SOSS displays in contact classification as either friendly or unfriendly targets. The unclassified name Project Caesar was given to cover development and installation of the resulting system.
A cover story was developed to explain the visible shore installations, the Naval Facilities, and the commands under which they fell. The cover explained that data gathered by oceanographic and acoustic surveys with ships could at times be collected "more expeditiously and more economically by means of shore stations. These are the U. S. Naval Facilities." The cover extended to the names of the commands and training of personnel with overall commands designated Ocean Systems Atlantic and Ocean Systems Pacific, and terms such as Ocean Technician [OT] and Oceanographic Research Watch Officer given to Naval Facility personnel. Despite being qualified for a warfare specialty and its symbols, the Navy personnel in the small SOSUS community could not do so for the sake of secrecy until the mission became public in 1991. The Ocean System commands, COMOCEANSYSLANT (COSL) and COMOCEANSYSPAC (COSP), then began to reflect their true nature as Undersea Surveillance commands COMUNDERSEASURVLANT (CUSL) and COMUNDERSEASURVPAC (CUSP) under the Integrated Undersea Surveillance System (IUSS) name that had come into effect in 1985 as systems other than fixed emerged.