thumb|upright=1.35|First SOSUS stations
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.
thumb|upright=1.35|The [[GIUK gap]]
The original system was capable of oceanic surveillance with the long ranges made possible by exploiting the deep sound channel, or 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.
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, 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.
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 refers to A2 on the musical scale, which is technically two A's 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.
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.
thumb|LOFARgram
thumb|right|LOFARgram writers on NAVFAC watch floor
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. 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. The unclassified name Project Caesar was given to cover development and installation of the resulting system. 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. In 1997 the RAINFORM was abandoned and replaced.
thumb|right|NAVFAC Nantucket showing Terminal building as internal security area
The original Naval Facilities and later, consolidated, processing centers were high security installations characterized by an outer security fence and gate checkpoint. The terminal buildings within were double fenced with separate entry security. Not all personnel assigned to the facility had access to the operational part of the installations. The early arrangement can be seen in the vertical photograph of Naval Facility Nantucket and later in the photograph of Naval Facility Brawdy below. Equipment in the terminal buildings was installed by specially cleared Western Electric Company personnel.
Initial installations
Western Electric and ONR representatives met on 29 October 1950 to draft a contract that was signed as a letter contract on 13 November to build a demonstration system. The contract was managed by Bureau of Ships (BuShips) with then Ensign Joseph P. Kelly, later Captain and termed "Father of SOSUS," assigned. An experimental six-element hydrophone array was installed on the island of Eleuthera in the Bahamas during 1951. Meanwhile, Project Jezebel and Project Michael focused on studying long range acoustics in the ocean.
From 2–19 January 1952 the British cable layer installed the first full sized, long, forty transducer element operational array in off Eleuthera in the Bahamas. Successful tests with a target submarine resulted in the order to install a total of nine arrays along the coast of the Western North Atlantic. The 1960 secret, limited distribution Navy film Watch in the Sea, contains a segment at about 9:22 minutes into the film concerning the search for a suitable array location and laying the array. It describes the operational arrays as being long. In 1954 ten additional arrays were ordered with three more in the Atlantic, six on the Pacific coast and one in Hawaii. By the 1980s improved communications technology allowed the array data once processed in individual Naval Facilities to be sent to central processing centers (Naval Ocean Processing Facility (NOPF)) for centralized processing of multiple fixed and mobile array information.
The first systems were limited by the commercial telephone cable technology for the application requiring a shore facility within about from the array and thus within that distance from the continental shelf locations suitable for the array. The upgrades made possible by the multiplexed coaxial cable were designated Caesar Phase III. Caesar Phase IV was associated with major upgrades in shore processing with Digital Spectrum Analysis (DSA) backfits at the stations replacing original equipment during the late 1960s. In September 1972 a third generation coaxial cable, again based on commercial developments at Bell Labs and designated SD-C, was installed for the system terminating at Naval Facility Centerville Beach, California. The SD-C cable was the basis for a fourth generation of sonar sets with installation of the Lightweight Undersea Components (LUSC) involving new shore equipment in 1984. In June 1994 an entirely new cable system was introduced with fiber optic cable.
Chronology
1950s
In 1954 the Fleet Sonar School at Key West established a Sound Search Course for training personnel. The highly classified program was behind the "Green Door" which became a name for the program itself as well as being seen as a term for the secrecy.
thumb|right|NAVFAC Cape May (1955-1962) Terminal Building on WWII Coast Artillery bunker before storm damage forced move to Fort Miles in Delaware where it became NAVFAC Lewes.
In 1954 three full systems to include a NAVFAC terminus were installed with arrays terminating at NAVFACs at Ramey Air Force Base, Puerto Rico in September, Grand Turk in October, and San Salvador in December. Systems terminating at Naval Facility Bermuda, Canadian Forces Station (CFS) Shelburne, Nova Scotia, Nantucket, and Cape May were installed during 1955. Systems terminating at Naval Facility Cape Hatteras and Naval Facility Antigua and two Evaluation Centers, forerunners of NOPFs, were established in New York and Norfolk during 1956. The initial array at Eleuthera got a fully functioning NAVFAC with an additional system for the Atlantic at Barbados and the first of the Pacific systems at San Nicolas Island came in 1957. During 1958 the remainder of the Pacific stations at Naval Facility Point Sur and Centerville Beach in California and Pacific Beach, Washington, and Coos Head near Coos Bay, Oregon were installed. Arrays of hydrophones placed around the target area located the missile warhead by means of measuring arrival times of the explosion at the various hydrophones of a SOFAR charge in the test warhead. During that period an atypical SOSUS system was installed in 1959 at Argentia, Newfoundland to provide surveillance for approaches to Hudson Bay. It was a shallow water, curved array with ten eight-element arrays installed on two cables with each cable having the capacity for the usual forty elements.
NAVFAC Argentia got a 2X20 element array in 1963. A 1965 decision to deploy systems to the Norwegian Sea was followed in 1966 with a system terminating at Keflavik, Iceland with the first 3X16 array system while Western Electric installed data links by land line to OCEANSYSLANT and OCEANSYSPAC. New systems were installed during 1968 at Midway Island and Guam. COMOCEANSYSPAC relocated to Ford Island, Hawaii from Treasure Island, California. The shallow water system at Argentia was deactivated. The satellite communications ship joined the project in 1967 for acoustic and bathymetric work.
1970s
The first NAVFAC decommissioning took place with the isolated duty station at NAVFAC San Salvador, Bahamas shut down on 31 January 1970. The old station is now home of the Gerace Research Center. NAVFAC Barbers Point is commissioned. A system wide modernization began in 1972. Argentia became a joint Canadian Forces and U.S. Navy facility. NAVFAC Ramey becomes NAVFAC Punta Borinquen in 1974. Further NAVFACs shut down in 1976 with NAVFACs Punta Borinquen and Nantucket decommissioned. NAVFAC Barbados was decommissioned in 1979. The facility () was adjacent to the Royal Air Force Station Brawdy which had returned to RAF control during February 1974 after closure in 1971.
In 1975 left Naval Research Laboratory service and joined Project Caesar. In April 1974 the ship was reported as already being funded by Naval Electronics Systems Command (NAVELEX), where the project program management resided, and no longer funded as an oceanographic ship. By 1979 it was the most recently built ship of the five project ships that then included cable repair ships Albert J. Myer and Neptune due for modernization and the larger repair ship Aeolus that was uneconomical to repair and marginal as a cable ship. Kingsport was still with the project. The Navy was requesting four fully functional cable ships, the modernized Albert J. Myer and Neptune and two large new ships. The two new ships were to be designed as modern cable ships, fully capable of cable and survey work. and a move from Arlington to San Diego in 1997.
Both undersea surveillance and the operation of U.S. submarines were tightly held secrets within the communities. That secrecy led to misunderstandings and even potential breaches of security. Despite periods of realization both communities fell back into assumptions as a result of secrecy. On the submarine force side, there was a recurrent idea that SOSUS/IUSS could not detect U.S. submarines, despite early SOSUS having tracked USS George Washington across the Atlantic. The realization that SOSUS could detect U.S. nuclear submarines led to the Navy's quieting program for those submarines and the assumption returned.
"Caesar fleet"
Other ships are mentioned as having "cameo" appearances and the project apparently made use of other Navy survey and civilian cable ships on occasion. The core fleet appears to be those listed below.
Cable ships:
Post-Cold War
By 1998 cable technology and shore processing allowed consolidation of shore stations to a few central processing facilities. Changes in Soviet operations, few hostile nuclear submarines at sea and the ending of the Cold War in the 1990s meant the need to maintain IUSS/SOSUS at full capability decreased.
National Oceanic and Atmospheric Administration (NOAA) Vents program at its Pacific Marine Environmental Laboratory was granted access to the system at the Naval Ocean Processing Facility at Whidbey Island in October 1990 to combine raw analog data from specific hydrophones with NOAA systems for continuous monitoring of the northeast Pacific Ocean for low-level seismic activity and detection of volcanic activity along the northeast Pacific spreading centers.
Woods Hole Oceanographic Institution detected and tracked a lone whale with a unique call over a period of years in the Pacific.
Texas Applied Research Laboratories, and several other organizations have used the system for research.
Associated systems
Colossus
Jezebel research had developed an additional short range, high frequency, upward-looking system using active transducers for direct plotting of ships passing over the array. Colossus was intended to be installed in narrows and straits.