page_title: SOSUS
section_title: Operational systems
hierarchical_section_title: SOSUS / Operational systems
caption_attribution_description: A U.S. Navy Lockheed P-3B Orion aircraft of Patrol Squadron 6 (VP-6) The World Famous Blue Sharks in flight near Oahu, Hawaii (USA), on 6 April 1978. VP-6 was established on 15 July 1943 as VB-146 and disestablished on 31 May 1993.
context_page_description: The Sound Surveillance System was a passive sonar system developed by the United States Navy to track Soviet submarines. The system's true nature was classified with the name and acronym SOSUS themselves classified. 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, being for oceanographic research. In 1985, as the fixed bottom arrays were supplemented by the mobile Surveillance Towed Array Sensor System and other new systems were coming on line, the name itself changed to Integrated Undersea Surveillance System. 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 system was capable of oceanic surveillance with the long ranges made possible by exploiting the deep sound channel, or SOFAR channel.
context_section_description: SOSUS systems consisted of bottom-mounted hydrophone arrays connected by underwater cables to facilities ashore. The individual arrays were installed primarily on continental slopes and seamounts at the axis of the deep sound channel and normal to the direction in which they were to cover. The combination of location within the ocean and the sensitivity of arrays allowed the system to detect acoustic power of less than a single watt at ranges of several hundred kilometres. SOSUS shore terminal processing stations were designated with the vague, generic name of Naval Facility (NAVFAC). As technology improved the output of individual Naval Facilities was consolidated at central processing centers designed Naval Ocean Processing Facility (NOPF).
  The first systems were limited by the commercial telephone cable technology for the application requiring a shore facility  within about 150 miles from the array and thus within that distance from the continental shelf locations suitable for the array. The cable of the time consisted of multi-pair wire connected to the forty hydrophones of the array. New coaxial multiplexed commercial telephone system cable, designated SB, using a single wire for all hydrophones allowed major changes with the prototype installed in 1962 at Eleuthera. 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.
  Cable technology and signal processing improved and upgrades were made to the original installations. Cable technology made it possible to site arrays further from shore into the ocean basins. New signal processing capabilities allowed for innovations such as the split array in which a single line array was divided into segments, each separately processed, then electronically recombined to form narrower beams for better bearing and cross fixes between arrays. Augmenting these local improvements was the increased central processing in centers that eventually became the Naval Oceanographic Processing Facilities. There the contacts of multiple arrays were correlated with other intelligence sources in order to cue and provide the search area for air and surface antisubmarine assets to localize and prosecute.
  The system was considered a strategic, not tactical, system at the time and part of continental defense. In military construction hearings during 1964 before the Senate Committee on Armed Services the request for funding of recreational and other support buildings for the Naval Facility Cape Hatteras the Navy noted it was part of a program supporting continental air and missile defense forces without mention of its role in tracking Soviet missile submarines.
caption: P-3B of Patrol Squadron 6 (VP-6).
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