First-Generation Installations and Initial Operational Experience

The first NAVFAC built by the Caesar program was commissioned in September 1954 at Ramey Air Force Base in northwestern Puerto Rico.3 Before the end of the year, similar stations were in operation at Grand Turks and San Salvador in the Bahamas, and by late 1957, additional NAVFACs had been established at Bermuda, Shelburne (Nova Scotia), Nantucket, Cape May4, Cape Hatteras, Antiqua, Eleuthera, and Barbados. A glance at the map of the eastern North Atlantic makes clear the rationale for siting these first-generation listening facilities. They form a huge semicircle from Barbados to Nova Scotia, opening toward the deepwater abyss west of the mid-Atlantic Ridge. This provided both excellent coverage of the deep ocean basin off the eastern seaboard and the opportunity for contact correlation among arrays with widely separated vantage points. For optimum acoustic coupling with the deep sound channel, the arrays “looked” outward from the edge of the continental shelf, and because cable lengths were limited to somewhat less than 150 miles, the NAVFACS had to be located at coastal sites where the shelf break came closest to land. Two years later, this concept of operations was expanded to incorporate a SOSUS station at Argentia, Newfoundland to process the outputs of
a number of shallow-water arrays south of the Grand Banks.

The year 1957 also saw the extension of SOSUS to the Eastern Pacific, with the installation of NAVFACs and associated arrays at – from south to north – San Nicholas Island, Point Sur, and Centerville Beach, California; Coos Bay, Oregon; and Pacific Beach, Washington. Still later, additional arrays would be terminated at Guam, Midway, Adak (in the Aleutians), and Barber’s Point near Honolulu.

Operationally, the Navy intended SOSUS to provide early warning of hostile submarines entering the North Atlantic or Eastern Pacific, as well as generating “cueing” information for area ASW forces. By combining bearing data from separated arrays “holding” the same contact, geographic “probability areas” of target position could be calculated and passed to patrol aircraft, surface ships, or submarines to facilitate reacquisition of the target for fine localization and prosecution. This concept of operations necessitated the establishment of regional SOSUS Evaluation Centers – later called Naval Oceanographic Processing Facilities (NOPFs), with the first two at Norfolk and New York – that correlated contact information from multiple NAVFACs with other intelligence sources, such as radio direction-finding. The NOPFs then forwarded the resulting target position estimates and probability areas to local and regional ASW commands.

The primary threat against which SOSUS was originally designed was snorkeling Soviet diesel submarines at the surface, and the system’s key technical characteristics – such as frequency coverage – were established accordingly. Fortunately, the resulting capability proved even more effective against deep-running Soviet nuclear-powered submarines when the first of these went operational in 1958. In a 1961 demonstration of the capabilities of the system, SOSUS tracked the USS George Washington (SSBN-598) across the North Atlantic on her first transit from the United States to the United Kingdom. Then, in June 1962, NAVFAC Cape Hatteras achieved the first SOSUS contact on a Soviet diesel submarine, to be followed a month later with the first detection of a Soviet nuclear boat west of Norway by NAVFAC Barbados. Later that year, during the Cuban Missile Crisis, the first positive correlation with a visual sighting was made, when a patrol aircraft confirmed the presence of a Russian FOXTROT-class submarine that had already been detected by NAVFAC Grand Turks. In 1968, NAVFAC Keflavik made the first SOSUS detections of Soviet CHARLIE- and VICTOR-class nuclear submarines, and that same year, SOSUS played a key role in locating the wreckage of USS Scorpion (SSN-589), lost near the Azores in May. Moreover, SOSUS data from March 1968 facilitated the discovery and clandestine retrieval years later of parts of a Soviet GOLF-class submarine that foundered that month north of Hawaii.

Subsequently, as increasing numbers of Soviet submarines from bases in the Barents and White Seas achieved access to the North Atlantic by rounding northern Norway and steering south through the Greenland-Iceland-United Kingdom (GIUK) gap, the decision was taken to extend SOSUS into more northerly waters, and new NAVFACS were established at Keflavik, Iceland in 1966 and Brawdy, Wales in 1974. Also, better processing and cable technology allowed siting arrays farther from
shore and using “split array” techniques in which a single line array was divided into segments whose outputs were processed separately and then re-combined electronically to achieve narrower beams and greater directivity. In 1974, Keflavik was the first NAVFAC to detect a DELTA-class Soviet SSBN as it moved down into the North Atlantic.

Photo caption follows This is a typical LOFARgram, in which frequency is portrayed along the horizontal axis and time along the vertical axis. The presence of spectral energy is indicated by a darkening of the paper. In this representation, a long, narrow, vertical line indicates a persistent narrowband component centered on a single frequency – perhaps a“tonal” caused by rotating machinery – along the bearing line of interest. Wider gray areas result from broadband noise sources or the ambient background.

Cold War Effectiveness – and Decline

As the Cold War deepened, and both the size and capability of the Soviet submarine fleet continued to grow, SOSUS became “the secret weapon” that enabled U.S. ASW forces to keep close track of virtually all potentially hostile submarines operating in the deepwater regions off both coasts. This capability was facilitated by geographical constraints that forced Soviet submarines into predictable deployment patterns and the rudimentary state of Russian acoustic quieting, which left their submarines some 30 dB noisier than U.S. counterparts – and hence easily detectable from thousands of miles away. In the mid 1980s, the network of fixed SOSUS arrays was augmented by a small fleet of civilian-manned, ocean-going, acoustic surveillance ships deploying the Surveillance Towed Array Sensor System (SURTASS), a towed line array over 8,000 feet long.5 By means of satellite communication links, contact information developed by the SURTASS ships at sea was passed to the SOSUS Evaluation Centers ashore and melded with data from the fixed arrays to establish position estimates for likely targets. In time, the totality of fixed arrays, shore processing facilities, and SURTASS ships became known as the Integrated Undersea Surveillance System (IUSS).

Photo caption follows
Eighteen first-generation SURTASS ships, of which USNS Indomitable (T-AGOS-7) is an example, were commissioned between 1984 and 1988. Largely civilian-manned, they displaced 2,260 tons on a length of 224 feet and deployed a towed line array more than 8,000 feet long on deep-ocean ASW patrols of 60–90 days duration.

Eventually, with the help of key information supplied by the Walker-Whitworth espionage ring6, Soviet intelligence learned of the existence of SOSUS and its remarkable success in tracking Soviet submarines at long range. Thus, beginning shortly after John Walker’s first treasonous revelations in 1968, the Russian navy embarked belatedly on a rapid submarine quieting program, and within five years, the radiated noise levels of their first-line boats had begun to drop recipitously. By the end of the Cold War in the late 1980s, Russian submarines were much closer to their U.S. equivalents, and the ability of IUSS to detect and track them at long range had deteriorated significantly. In an attempt to regain some of the acoustic advantage lost to Soviet quieting, IUSS system developers turned from long line arrays and their fans of pre-formed beams to large fields of simpler, “upward-looking” hydrophones densely distributed on the ocean floor, each capable of detecting submarines only in its immediate vicinity. Thus, detection and localization were subsumed into a single process, and the first “Fixed Distributed System” built in accordance with this strategy was deployed in 1985.

Moreover, with steady improvements in acoustic signal processing through the 1970s and 1980s, the first generation of shore-processing hardware, which turned out hundreds of single-beam LOFARgrams – 24 hours a day, every day – was gradually replaced by computer-based workstations that could analyze the incoming acoustic data digitally and display it on multiple computer screens. Additionally, to reduce manpower requirements and achieve other efficiencies, most of the original arrays were re-terminated at alternative shore sites or “remoted” to central processing facilities, which led to a steady reduction in the number of operational NAVFACs. These transitions were completed in 1997 and 1998, but by that time – ironically – quieter submarines, major changes in Soviet operating patterns, and finally, the end of the Cold War had already eliminated much of the justification for maintaining IUSS at its full capability.7

Photo caption follows
(above) The Soviets built more Delta-class SSBNs – 47 in four variants – than any other class of ballistic missile submarine. The first Delta I appeaered in 1972; the last Delta IV was completed in 1992. The earlier boats displaced 11,750 tons submerged and carried 12 strategic missiles. The later variants added approximately 2,000 tons and four more missiles. SOSUS first detected a Delta at sea in 1974.
Photo caption follows (left) Between 1958 and 1982, the Soviet Union built approximately 80 Foxtrot-Class conventionally-powered submarines, of which nearly 20 were intended for export. Displacing 2,400 tons submereged on a length of 300 feet, the Foxtrots became the workhorse of Russia’s diesel-powered submarine force during the height of the Cold War. Snorkeling conventional submarines were SOSUS’s original targets, and the first of these was detected in 1962.

IUSS Today – and Future Prospects

Today, while the Navy maintains a number of SOSUS arrays in either operational or standby status, only three shore facilities at Dam Neck, Virginia, Whidbey Island, Washington, and St. Mawgan, United Kingdom8 – remain to process their dwindling output. With few possibly-hostile, nuclear-powered submarines still operating at sea and modern, quiet, diesel-electric boats essentially undetectable at long range by passive means, there’s not a lot to listen for anymore, and targets of potential interest are rare. However, several existing arrays have achieved well-publicized successes in peacetime pursuits such as tracking migrating whales and detecting illegal driftnet fishing on the high seas. Moreover, as the Navy explores the use of low-frequency active (LFA) acoustics for detecting and tracking quiet submarines in the future, both the fixed arrays and the remaining SURTASS ships may well play an important role as adjunct or bi-static receiving sites.

When it was first suggested over 50 years ago as a means of exploiting contemporary oceanographic findings and state-of-the-art technology for wide-area undersea surveillance, SOSUS was an audacious concept, and its successful implementation was one of the most impressive engineering feats of the early Cold War. Later, during the most dangerous phases of that simmering conflict, IUSS gave the United States an unprecedented capability for long-range submarine detection and strategic early warning that we can only envy today in this new era of asymmetric threats.

Dr. Whitman is the former Senior Editor of UNDERSEA WARFARE Magazine. Much of his long Navy technical career was involved with SOSUS and undersea surveillance. Earlier, as a graduate student at MIT’s Speech Communications Laboratory, he was responsible for the maintenance and calibration of the sound spectrographs that only a few years earlier had evolved into SOSUS’s LOFAR signal processors.


Cote, Owen R. Jr., “The Third Battle: Innovation in the U.S. Navy’s Silent Cold War Struggle with Soviet Submarines,” MIT Security Studies Program, March 2000 (available at

Tyler, Gordon D., Jr., “The Emergence of Low-Frequency Active Acoustics as a Critical Antisubmarine Warfare Technology,” Johns Hopkins APL Technical Digest, Vol. 13, No. 1 (1992)

Urick, Robert J., Principles of Underwater Sound, 2nd Ed., McGraw-Hill, New York, 1975

Weir, Gary E., An Ocean in Common, Texas A&M, College Station, 2001

Additionally, two websites have provided useful information and general background:
(Home page of the IUSS-Caesar Alumni Association)

1 In deep-water sound propagation, a convergence zone (CZ) is a circular ring of anomalously-low transmission loss that is caused at predictable distances from a submerged sound source by the near-surface bunching of sound rays that originally left the source over a narrow range of vertical angles. Typically, CZs appear at multiples of 30 to 35 miles from the source, but the specifics are highly dependent on the SVP and local bathymetry. Generally, much higher-than-normal target-detection probabilities are observed in the CZs.

2 By 1950, a Navy SOFAR explosion had been heard over 3,500 miles away. Moreover, several rudimentary experiments in tracking submarines with the net had shown favorable results.

3 When Ramey AFB was disestablished in 1973, the NAVFAC remained in operation but was renamed Punta Borinquen.

4 After NAVFAC Cape May was destroyed by a hurricane, it was replaced in 1962 by a new facility at Lewes, Delaware.

5 The initial first-generation SURTASS ship was USNS Stalwart (T-AGOS-1), commissioned in April 1984. The last of the 18 ships of that class entered service four years later.

6 John Walker, Jr. was a U.S. Navy warrant officer and career submarine communications expert who over a period of 15 years sold countless naval messages and the keys to decipher them to the Soviets, thus revealing a vast amount of highly sensitive information about U.S. naval operations and capabilities. Later, Walker recruited another Navy communications specialist, Jerry Whitworth, his brother, Arthur, and even his own son, Michael Walker, before he was turned in by his wife. All four men were arrested in 1985 and subsequently prosecuted, but by then, enormous damage to U.S. security had occurred.

7 By 1991, the existence and missions of SOSUS and IUSS had been formally declassified.

8 NOPF Dam Neck was established in 1980 as part of a major consolidation of the Western Atlantic arrays. NOPF Whidbey Island was created in 1987 to perform a similar function for the Pacific. The Joint Maritime Facility (JMF) St. Mawgan, operated in conjunction with the United Kingdom, replaced the former NAVFAC at Brawdy, Wales, in 1995.

Cover of Undersea Warfare Magazine Winter 2005