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Mr. Merrill is afreqnent contributor to THE SUBMARINE REVIEW and is a published author of several books on the history of undersea technology. He is a retired engineer with lengthy experience at the New London Lab of the Naval Undersea Warfare Center. He currently lives in Watetford, CT.

Mr. Merrill was recently awarded the JOHN GARDNER MARITIME RESEARCH AWARD by the fellows of the G. W. Blullt White Library at Mystic Seaport.

Part I appeared in the July 2007 issue of THE SUBMARINE REVIEW

Caesar First Steps

In June 1952, with the successful LOF AR detection of submarines at Sandy Hook and Eleuthera and long experience with SOF AR, the Chief of Naval Operations (CNO) directed Bureau of Ships to acquire six stations under CAESAR, increasing to nine stations in September. Three contracts were implemented to include equipment, installation, and construction or expansion of a cable-manufacturing facility. The Simplex Wire and Cable Company in New England was expanded to manufacture the miles of cables needed for Caesar installations.

In a 1952 letter to CNO, the Commander in Chief of the Pacific Fleet indicated interest in the system and offered suggestions regarding Pacific Ocean locations for future sites. By May 1954, ten more stations were planned with six on the West Coast. An unclassified cover story was created for the new system and the low frequency passive detection development was designated SOSUS.

During the next five years, SOSUS facilities were installed and commissioned along the eastern Atlantic Ocean. “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. “23 Likely Soviet submarine routes to gain access to the United States eastern seaboard provided a basis for the location of SOSUS hydrophone arrays.2~ The results of Lt. Cmdr. Joseph Kelly’s efforts during the first years of the project are shown in the table.

Project Caesar Stations Commissioned 1954-59 1954 Ramey, Puerto Rico-Grand Turk-San Salvador 1955 Bennuda, Shelburne, Nova Scotia, Nantucket, MA, Cope Mny, NJ 1956 Cape Hatteras, NC, Antigun 1958 Point Sur, CA, Center ville Beach, CA, Pacific Beach, WA, Coos Head, OR, Argentia, New found land

Caesar Cable Fleet Ships

WHOI, SOI, and Columbia University’s Hudson Laboratory under Project Michael dealt with finding answers to questions regarding cable placement. The Navy cable ships and AT&T accomplished the actual laying of the hundreds of miles of cables in depths up to 1000 fathoms. Initially the cable ships NEPTUNE and MYER were assigned. Later, ships THOR, AEOLUS, MIZAR, HUD DELL, ZEUS and USNS WATERS made up the cable fleet. They became known as the Caesar Fleet. Some locations where deep water was available needed ten or twenty miles of cable while others required a hundred miles. At some point in the SOS US years, 30,000 miles of undersea cable and more than 1000 hydrophones were maintained.


The shore station facilities located along the coasts with their hydrophone arrays, buildings, and instrumentation came to be identified as NA VF ACS. Sites were chosen where the continental shelf break came closest to land. Upon the completion of the installation and in operation, sufficient manpower for the daily 24-hour operation placed a requirement of 100 or more personnel at each facility. The unique skills for reading and interpreting the LOF AR analyzer’s black and grey paper printout made training and education important requirements.

The number of LOF AR analyzers at each NA VF AC was quite large “A Lo far analyzer was associated with each beam of each array served by a NAVFAC, and typically, the large watch floors were filled with hundreds of these “gram-writers: busily turning out Lofar grams on ‘smoky paper 24 hours a day. “’27 Equipment maintenance, data collection and its transfer to centers for analysis and operational commands provided continuing challenges. Eventually more than twenty stations were in operation and met a man-power requirement of several thousand.

Continuing SOSUS Expansion and Operational Example

With the above clusters of stations in 1956 and more to follow, the concept of regional SOSUS Evaluation Centers was adopted to correlate contact information and provide reacquisition data concerning the target for use by patrol aircraft, surface ships and submarines. Later, the Centers were called Naval Oceanographic Processing Facilities (NOPFs). The first two were in Norfolk and New York. Combined with other intelligence, the resulting target position estimates and probability areas were provided to local and regional ASW commands.

At the end of the 1950s, “SOSUS cables and hydrophones, separated by intervals of five to fifteen miles, were also laid off Denmark, Iceland, Norway, the North Cape, Italy, Spain, Turkey, and around the British Isles.”

Expansion of SOSUS stations was modest in 1961 with one NA VF AC placed in operation at Adak, Alaska, not far from the western tip of that state. On the operational side, as a demonstration, East Coast United States SOSUS arrays successfully tracked the first Fleet Ballistic Missile submarine, USS GEORGE W ASHJNGTON (SSN 598) on its first transit from the United States across the North Atlantic to the United Kingdom.

1962 Soviet Submarines and SOSUS

The Cuban Missile Crisis (July-November 1962), provided opportunity for the Atlantic SOSUS stations to have an important role in the naval blockade. The heightened time was during October. In June, the SOS US NA VF AC at Cape Hatteras identified the first Soviet diesel. The following month, NAVFAC Barbados made the first detection by SOS US of a Soviet Nuclear submarine as it crossed the Greenland-Iceland-UK gap.” …

SOSUS was able to exploit the fact that both propellers and rotating machinery mounted directly to a submarine’s hull generated, predictable narrowband tonals at source levels high enough for large LOF AR arrays to detect them and track them on an ocean wide basis.” From SOSUS data, Neptune naval aircraft (P2s) were able to broadcast in the clear the exact locations of Soviet Submarines and were heard by the Soviet submarines as well as blockade members.31 ASW aircraft, in addition to the cueing advantage by the long range SOSUS detection data, were further enhanced by the use of their aircraft launched sonobuoys in the pursuit of the Soviet submarines.

During October at the peak of the crisis, Soviet Foxtrot submarines (nuclear torpedo equipped), in transit to and in the Cuban area were detected by SOSUS and closely trailed. The tracking data was passed to the Navy blockade participants. After the crisis was resolved, the observed SOSUS effectiveness led to the expansion and upgrading of the network. A SOSUS array was placed to cover the Greenland-Iceland-United Kingdom (GIUK) Gap with NA VF AC Keflavik established in 1966. One path for Soviet Submarines to the Atlantic and the United States from the northern Soviet submarine base was through the Gap.

Data from these widely-distributed arrays brought attention to new uses for the underwater surveillance. In 1965-66, the Norway SOSUS array detected and tracked Soviet Bear-D bombers flying over the Norwegian Sea. Surface ship detection as well as detection of nuclear explosions occurring near oceans or underwater was included in SOSUS capability. With 55 Soviet nuclear submarines deployed between 1958 and 1968, opportunities for SOSUS detection were increased.


On Sunday April 9, 1963, THRESHER was lost with all hands at a depth of 8400 feet 260 miles off the New England coast. Nearby oceanographic ships and others were able to identify an area of interest. A chronology of SOSUS for the year of the tragedy cites “SOSUS plays critical role in pinpointing the location of the incident.”

Strong interest in determining the cause of the submarine loss was directed at the obvious to prevent future similar events. In this regard, resolution of the question of whether the loss might be due to deliberate enemy action was critical.34 Was the loss from an explosion or implosion? The Navy’s Deep Submergence Rescue Vehicle (DSRV) development was one of the results of the loss of the THRESHER.

1968: Soviet K-129

In 1968, SOSUS Pacific operations included a new operational NA VF AC at Midway Island and the commissioning of the Guam, Mariana Islands NA VF AC. First SOSUS detections of Victor and Charlie Class Soviet nuclear submarines occurred at the Keflavik, Iceland station.

SOSUS involvement occurred with the April loss of the Soviet ballistic missile, first Soviet submarine with underwater launch, diesel electric GOLF (K-129) submarine in the Pacific northwest of Hawaii and a few weeks later on May 27 with the loss of the USS SCORPION (SSN 589) in the Atlantic in water with depths of the order of 15,000 feet.

The mid-Pacific SOSUS array (code-name Sea Spider: a 1,300-mile-long circular array surrounding the Hawaiian Islands) has been cited as the array that monitored and localized the breakup of the Soviet submarine K-129.

In both submarine losses, sound surveillance data contributed to the overall effort to determine the location of each lost submarine. The United States search for SCORPION was undertaken with reasonable public exposure while the Soviet search was extremely classified. The United States search for the K-129 included careful security measures. Searching for the submarines at great depths and, in the case of the Pacific location, of the order of 15,000 feet or greater made the searches extremely difficult and complex. Developing accurate information concerning the reasons for the losses provided a broad number of challenges.


Regarding SCORPION loss on a return trip to the United States, it was realized that during a three thousand mile track from southern Europe, the sounds of its collapse and the implosions at collapse depth might have been recorded. A Naval Research Laboratory (NRL) research station in the Canary Islands equipped with a hydrophone found about five separate trains of acoustic events that could have been associated with a submarine breakup.

In addition, “Kelly (now a Captain) came to the rescue with his awareness of a super-secret hydrophone installations in the hands of another government agency. The sounds of SCORPION’s death might be buried in this organization.” Captain Kelly’s resourcefulness led to additional Scorpion acoustic signatures. Collectively the signatures and using triangulation identified a location for SCORPION. The following year, the deep submergence vehicle Trieste II provided further details of SCORPION’ s sinking. The SCORPION was 400 miles southwest of the Azores at 10,000 feet.

Continuing interest in SCORPION recently in the 2006 book Silent Steel brings further revelations regarding the search for the submarine.39 The author points out that it was the additional acoustic signal picked up by the Air Force’s Technical Applications Center (AFTAC) facility in Argentia, Newfoundland. The facility’s purpose was monitoring Soviet nuclear weapon tests. AFT AC’s implosion data coupled acoustic data from the SOF AR operation on La Palma, a small island in the Canary Islands that identified the submarine’s location.

High point

Under Captain Joseph Kelly, SOSUS grew in size, improved its operations and methods, and more than met its purpose. At the time of his retirement in April 1973 after more than 20 years as SOS US Project Manager, there were a total of22 SOSUS installations along the East and West Coasts of the United States.

SOSUS success in the 1970s and the availability of effective air-dropped homing torpedoes and more intensive use of the P3 Orion patrol squadrons allowed the U.S. submarines to adopt a barrier strategy in the Norwegian Sea, along the Greenland-United Kingdom line, and at choke points in the North Pacific.40 ln summary, “By 1981, unclassified depictions of SOSUS described it as having 36 installations, including facilities located in Continental United States (CONUS), the United Kingdom, Turkey, Japan, the Aleutians, Hawaii, Puerto Rico, Bermuda. Barbados, Canada, Norway, Iceland, the Azores, Italy, Denmark, Gibraltar, the Ryukyus, Panama, the Philippines, Guam, and Diego Garcia.”

SOSUS Eclipsed

The mid-I 980s brought several technology changes that challenged SOSUS ‘s role. The Soviet submarine ballistic missile range changed from the early days of SOS US. The Soviet initial range of 350-1600 nautical miles (nm) increased to ranges of the order of 4900 nm. This enhancement placed Soviet ballistic missile submarines closer to the USSR, typically further from SOS US locations.42 Soviet SSBNs no longer needed to pass through the SOSUS barriers to reach their targets. Soviet SSBN patrols could be conducted in the marginal ice seas of the Soviet Arctic littoral, including the Norwegian and Barents Seas and later under the permanent ice of the Arctic Ocean, and be provided with support by the rest of the Soviet Navy.43 SOSUS was beginning to be perceived as an aging system and not capable of covering large mid-ocean areas.

During the period 1967 to 1985, John A. Walker, a U.S. Navy warrant officer and career submarine communication expert watch officer in Norfolk, VA, continuously shared submarine information with the Soviets until 1976 when he retired and afterwards. In 1985, he was taken into custody. Soviet knowledge of SOSUS success contributed to the rapid quieting of Soviet submarines, making them more difficult noise sources to detect and localize.

Towed Sonar Arrays

In the late 1960s, there was significant and growing interest in the use of towed sonar arrays for ASW. As a result, by September 1970 systems were installed on three Dealey class destroyers in the Mediterranean. Demonstrations of these arrays were eminently successful. “During their stay in the Mediterranean, they accounted for over 50% of all submarine detections by any method, including visual sighting.”

The comments of Rear Admiral J. R. Hill, RN, regarding towed arrays in a 1984 assessment of ASW was one of the many statements that emphasized the significance of towed array development. “The passive sonar towed array … may well be the most important single development in ASW sensors since 1945.”

Surveillance Towed Array Sensor System (SURT ASS)

Gradually quieter Soviet submarines of the 1960s and 1970s created a need for mobile towed array detection. In the mid-l 970s, the Navy contracted with the Hughes Aircraft Company to develop the equipment for mobile surface ship detection. The latest computer technology for the computer-based sonar was expensive and required long development time. As a fixed system, SOSUS presented a wartime target and restriction to operate in certain areas. With its mobility SURT ASS complemented SOSUS. Further enhancement for the undersea surveillance came from active and passive sono-buoys.


Towed array ships required special design to accommodate the equipment, long arrays and extended patrols. In 1984, the first SURTASS ship of 18 United States Navy Ships for the Hughes developed equipment and arrays was commissioned. It was a mono-hull design and manned with a civilian and military crew. The ships are 224 feet long, beam of 43 feet displacing 2,262 tons, with a speed of 11 knots, and capable of ASW patrols of 60-90 days.48 SURTASS ships require stability at low speeds and in rough waters.

The towed linear array of 8575 feet was deployed on a 6000 ft neutrally-buoyant cable. SURTASS ships are manned with civilian mariners under contract to the Military Sealift Command and are designated United States Naval Ships (USNS). Ports of operation include Glasgow, Scotland; Rota, Spain; Yokohama, Japan; Pearl Harbor, Hawaii; and Port Hueneme, California. At this time, SURTASS joined SOSUS, and the combined name for these two systems became the Integrated Undersea Surveillance System (IUSS).

SUR TASS vessels send, via satellite, the gathered data on ocean sound signals and other target information to East and West Coast shore-based processing stations for transmittal to numbered fleets. These ships improved the Navy’s ability to locate Soviet submarines and monitor their fleet bases, but a wartime environment would restrict them to deep ocean areas.

End of Cold War and New SOS US Users

The official date for the end of the Cold War, December 26, 1991, brought a lessening of the need for SOSUS, and the system mission was declassified after forty-one years of secrecy. That year, Federal scientists in Newport, OR began to use SOSUS to listen to seaquakes, quickly detecting thousands of them. In 1993, the scientists monitored the explosive fury of a deep-sea volcanic eruption and sent a small flotilla of research ships, robots, and submersibles to explore the site.

Year Amount (million)
1991 $335
1994 $165
1995 $ 60 (estimate)

The status of SOS US is reflected in the budget table. A steady reduction occurred in the manpower assignments with 2500 for 1993, 2000 for 1994, and 750 for 1996. SURTASS technology and the end of the Cold War eclipsed SOSUS’s position. It diminished the need for global surveillance while the SURTASS technology offered mid-ocean coverage and mobility.

New uses for SOSUS began. In 1992, the Navy, the National Marine Fisheries Service and the Coast Guard used SOSUS to track fishing vessels in the Pacific to explore possible enforcement of international bans on drift-net fishing. Over a two-year period ( 1992-93), biologists used SOSUS to track the migrations of whales including a single blue whale as it swam southward from Cape Cod to Bennuda to Florida and back to Bennuda. All told, for about 1700 miles it was closely monitored .

To accommodate downsizing, SOSUS hydrophone arrays in both the Atlantic and Pacific became involved in shutdowns and closings. To reduce manpower requirements and realize other efficiencies, most of the original arrays were retenninated at alternative shore sites or remoted to central processing facilities that allowed a reduction in the number of operational NAF ACs. These transitions were completed in 1997 and 1998.

As mentioned previously, IUSS (formed in the mid-1980s to bring SOS US and SURTASS under one head) is made up of fixed, mobile, and deployable acoustic arrays that provide vital tactical cueing to ASW forces. It is the Navy’s primary means of submarine detection, both nuclear and diesel, continuing as an effective force multiplier, and in the post-Cold War period provides mobile detection, tracking, and reporting of submarine contacts at long range.’2 IUSS claims more contact holding hours since 1997 than all other anti-submarine warfare (ASW) platforms combined.

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