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Mr. Merrill is a frequent 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 Waterford, CT.

SOSUS, initially an experimental and growing concept to provide long-range detection capability using the underwater propagation of low-frequency sound, began in 1950. SOSUS, the classified name, was established in 1952. The system became an exemplary Cold War tool. SOSUS arrays, along with nuclear submarines optimized for ASW and long-range maritime patrol craft, became the dominant tools in the U.S. Navy ASW posture in the mid and late 1950s. It was strategic early warning.

Because SOSUS monitoring stations were fixed and shore-based, they were resistant to destruction, foul weather, and ambient self-generated noise. A SOSUS station consists of hydrophones mounted on the floor of the ocean and connected by cable to processing equipment ashore. The unprocessed data including ocean sounds and those of submarines are sent to processing centers for determination of whether they are a positive submarine contact. Appropriate action is then taken. Building and operating the early facilities, eventually almost on a global scale, with 1950 technology provided a significant challenge.

The system was still growing and improving during the late 1970s. After 41 years of service, in 1991 the system mission was declassified. The international setting for these SOSUS years included the Korean War, Cuban Missile crisis, Vietnam War, and the ever-present Cold War,

SOSUS was developed, implemented, and operated under conditions of utmost secrecy. During its operation, there was continual and increasing pressure from a determined, highly competitive, and on occasion effective Cold War enemy. Furthermore, the ultimate global reach and scale of the system required unceasing effort to accommodate the shifting international scene. Complex challenges were omnipresent. System performance was improved with better technology.

The system’s objective is to identify the general area where a submarine might be operating, filter out most man-made sounds and identify the acoustical wave from the submarine’s engines and propellers. With this data, the bearing, depth, and distance to the source of the sound may be determined and identification of the source is possible. In addition to monitoring ocean noise, ships, submarines, noise from planes flying over the ocean and falling rain were identified. An oceanographer’s comment about SOSUS in 1996 is appropriate, “It’s unique. It’s the only way to keep track of what goes on in the ocean.

It is interesting to note that the oceanographic research and observations made in 1937 by Maurice Ewing in conducting seismic studies at the Woods Hole Oceanographic Institute (WHOI) provided the basis for the initial SOSUS installation in 1952. sos us technology consisted of hydrophones on long underwater cables laid along the shore leading to the continental shelf.

Considering advances in Antisubmarine Warfare (ASW), a 1980 remark is apt ” … in both the Atlantic and the Pacific, SOS US is capable of fixing the position on an enemy submarine within a radius of 50 nautical miles or less.”3 A later comment in 1986, made by a Massachusetts Institute of Technology assessment of a SOSUS satellite-linked capability ” … at its best it can pinpoint the location of older (and therefore noisier) Soviet subs to within ten miles of their actual position from a distance of ten thousand miles, and that a twenty-five mile fix from several thousand miles is feasible in most cases.”

Examining the SOSUS system, it is important to consider the major challenges met eventually to have a system of twenty stations operating in three oceans. Further, there was responsibility for disseminating the collected data on a time-urgent basis to a number of addressees. Incorporating technological improvements and upgrading presented significant demands on the system providers and operators. Managing a fleet of seagoing cable-laying ships was another large and significant undertaking that was a part of the system.

By 1994, $16 billion had been invested for the system’s construction, implementation, and operation. “At its peak, in the late 1980s, the monitoring system cost more than $300 million a year to maintain and was staffed by 2,400 officers and technicians.”s With remission from Cold War demands in 1989, the system continues as a new tool for scientists seeking new knowledge and understanding of the ocean bottoms and their characteristics. New applications for the system include gaining knowledge relevant to global warming as well as the general environmental science of the world’s oceans.

Simply referring to SOSUS in a historical context as an important Cold War participant does not do justice to the vastness and global aspects of the system in its implementation and integration into the Navy’s needs. Time, cost, technology improvements and personnel considerations, including military and industry participation were as enormous as its Atlantic and Pacific Ocean coverage. The high security classification of the system always provided further demands on all concerned.

Initial interest in this surveillance concept stemmed from the improvements occurring in the Soviet submarines by their post World War II (WWII) acquisition of German submarine expertise. These Soviet submarine improvements necessitated countermeasures. Sound surveillance became an excellent countermeasure. As the Cold War progressed, Soviet submarines became quieter and the bar for surveillance was raised. With regard to the Cold War, the United States and Soviet submarines operated on a war footing in a time of peace.6 The role of SOSUS was a key element in countering the enemy submarines.

Similarly, the technical origins of the concept are of interest in iewing the logic of how and why SOSUS evolved. The significant way in which the system grew and improved should not be overlooked when reviewing the history.

Of the many participants in the evolution of SOSUS, it is essential that particular consideration be given to Navy Captain Charles Paul Kelly’s important role, as Project Engineer from the earliest days of the system implementation until 1973.

A 1968 accounting of the number of Soviet submarines by Jane’s Defensive Ships in 1968 lists 55 nuclear and 325 conventionally powered. About this time, there was awareness of Soviet submarines with depth capability of 1000 feet or greater and speed of 40 knots underwater. An operational SOS US was well suited to detecting and locating the growing and improving Soviet submarines as a threat to the United States as they extended their operating areas It has been noted that “in the new age of nuclear propulsion both the United States and the Soviet Union had studded the ocean bottom with networks of sensors and hydrophones in a technological race to render the oceans transparent, to “bug” the seaways and gain advantage in the silent war.

Before 1950: A Sound Pipeline
On October 17, 1937, geophysics professor Maurice Ewing from Lehigh University joined Columbus lselin, then Physical Oceanographer at Woods Hole, aboard the Woods Hole Oceano-graphic Institute ATLANTIS for a test cruise. Ewing conducted seismic refraction experiments to determine the thickness and makeup of sediments at the ocean bottom at depths of three miles in the North Atlantic.

Underwater explosives (I 0-pound TNT blocks) were used as sound source, and it was noted that a chain of echoes were gener-ated by repeated reflections between the ocean bottom and the sea surface especially at the lower frequencies and traveled long distance underwater with limited loss. Further, if hydrophones were carefully located in this deep sound channel, the signals could be detected. Important implementation of this channel identification followed but not immediately.

During World War II in 1942, Maurice Ewing with J. L. Worzel at WHOI resumed work on deep sound channel signal propagation proposed by Ewing in 193 7. Ewing theorized that low-frequency waves, which are less vulnerable than those of higher frequencies to scattering and absorption, should be able to travel great distances if the sound source is placed correctly. Jn analyzing the results of this test, they discovered a kind of sound pipeline, which they called he Sound Fixing and Ranging (SOF AR) channel, also known as the deep sound channel.

An additional test was conducted in the spring of 1944 aboard the research vessel RIV SALUDA operating in the vicinity of Eleuthera in the Bahamas. A deep-receiving hydrophone was hung from RIV SALUDA. A Navy ship dropped 4-pound explosive charges set to explode at 4000 feet in the ocean at distances up to 900 miles from RIV SALUDA’s hydrophone. The Navy ship’s operations were limited to this distance. Receivers located in Dakar on the west coast of Africa easily detected the underwater explo-sions at a range of the order of 2000 miles. Ewing and Worzel beard, for the first time, the characteristic sound of a SOFAR transmission, consisting of a series of pulses building up to its climax.

In 1943, an application of Ewing’s deep sound channel involved setting up coastal hydrophones to listen for the sound bursts from small explosives set off by pilots downed at sea while floating on life rafts to provide bearings for their location and retrieval. At that time, having a small TNT charge in conjunction with high-test aviation gasoline was deemed dangerous. In 1947, SOFAR was developed further and Pacific listening stations were established.

Concurrently, Ewing tried to get the Navy to use the deep sound channel to locate and summon help for a submarine under enemy attack. This was not pursued due to difficult coding problems.8 Later, Ewing’s deep·water channel discovery provided a basis for the mid-century Sound Surveillance System (SOSUS).

eace in 1945 did not end the Navy’s requirements for further information about the seas. Shortly after several years of an uneasy peace, international politics and technological innovations applicable to ships, submarines, aircraft, and weapons collectively brought additional high priority ocean·related Navy needs.

Encouragement to continue advancing ASW tactics and systems was stimulated when the details of German submarine developments became known near the end of the war. In the early postwar period, two Type XXI submarines became available to American, British, and Soviet navies. Increased underwater submarine speed ( 17 knots for up to 30 minutes), and the snorkel provided new challenges with oceanographic implications. Interest in submarine operating depths of 1000 feet also became a consideration. These technology advances strongly influenced submarine design and affirmed the importance of ASW.

The new Office of Naval Research (ONR) established in August 1946 and the National Science Foundation (NSF) created in 1950 by an Act of Congress provided an environment for the support of science in the United States. At first, ONR was the principal supporter of fundamental research by U.S. scientists. Success of federally-sponsored research was partly due to government-university-industry relationships brought about by ONR.

Ewing, by then a professor at Columbia University, found support in 1946 at ONR to continue research on the deep sound channel in Bermuda. The research site was called the Navy SO FAR Station. The initial installation consisted of a hydrophone on the bottom at 800 fathoms and connected to the shore by a submarine cable.

Committee on Undersea Warfare (CUW)
In November 1945, Gaylord P. Harnwell, director of the California University War Research Laboratory of ASW and pro· submarine research at San Diego, wrote a letter to Admiral Harold Bowen, then head of the Navy Office of Research and Invention, soon to be head of the Office of Naval Research (ONR). Harnwell called for an undersea warfare committee to “maintain Naval liaison, determine membership, organize and conduct symposia, issue bulletins and summaries of proceedings.

Support for Antisubmarine Warfare (ASW) research came in January 1946. Admiral Chester A. Nimitz, Chief of Naval Operations, reported to Secretary of the Navy James Forrestal that advances in submarine design and operating capability necessitated improvements in submarine detection and location systems.

A September 1946 proposal to Admiral Bowen, now head of ONR, recommended establishing a permanent Committee on Undersea Warfare (CUW). The new committee, established October 23, 1946, reported directly to the executive board of the National Research Council (NRC), the active arm of the National Academy of Sciences (NAS). The NAS established the CUW and provided the committee with a broad pro-and anti-submarine mandate. The committee’s charter allowed direct access with the executive board of the NRC, ONR, and Navy bureaus.

The environment during these years focused on the antisubmarine problem from the viewpoint of the German Type XXI submarine performance and snorkel mentioned above. Soviet submarine buildup using advanced German submarine technology was a continuing threat.

ATTENTION TO DEEP CHANNEL PROPAGATION 1949 Submarine Development Groups I, 2

An important Navy response to the threat occurred in January 1949, when the Chief of Naval Operations (CNO) directed that “Fleet Commanders assign one division in each fleet to the sole task of solving the problem of using submarines to detect and destroy enemy submarines. All other operations of any nature even type training, ASW services or fleet tactics shall be subordinated to this mission. To this end, two Submarine Development Groups were established: Group 1 in San Diego and Group 2 in New London at the Submarine Base. Investigation of the propagation characteristics of low frequencies was an early assignment. Group 2 at New London was tasked with “solving the problem of using submarines to detect and destroy enemy submarines.”12•13 Gradually Group 2 ‘s activities and mission expanded, and in the late 1970s it became Submarine Development Squadron Twelve.

With their assigned submarines, the Development Groups immediately initiated efforts to learn more about passive detection of submarines and submarine acoustic signatures. Further attention to deep channel propagation came from Naval Research Laboratory SOFAR tests off Point Sur, California. Using SOFAR hydrophones, submarine detection ranges of l 0-1 S nautical miles were reported. The above-mentioned Bermuda SO FAR installation provided additional information regarding passive detection. The experience from these SOFAR sites provided knowledge for hardware associated with shore-based detection of sounds in the ocean.

In May 1949, at the request of Submarine Development Group 2 in New London, the work at the Bermuda SOFAR station included making acoustic signatures of fleet type submarines and snorkel-equipped submarines. Enemy submarine acoustic signatures would play an increasing important role in the evolving surveillance system. Submarine detection ranges were made from about two miles to 100 miles.17 There was additional interest in SOFAR related to determining missile impact locations.

1950 Undersea Surveillance Support
Additional encouragement to pursue new antisubmarine research and development directions came from an April 1950 report (commissioned in 1949), Studies of Undersea Warfare by Deputy ChiefofNaval Operations (CNO) Rear Admiral F. S. Low and referred to as the Low Report. A 1984 comment by Willem Hackman in Seek and Strike noted the Low Report as bringing attention to priorities for future research and development with awareness of the forthcoming nuclear submarine and long-range torpedoes.

Further incentive to consider use of Ewing’s sound channel at low frequencies (30 -150 Hz) resulted from the CUW Fifth Undersea Symposium held in Washington on 15 and 16 May. Frederick Hunt, director of the Harvard Underwater Sound Laboratory during WWII, presented a paper favoring the use of the sound channel for long-range signal detection. The period from the start of the Korean War June 1950 to the armistice July 27, 1953 provided additional attention to defense issues and planning.

Project Hartwell
All the above undersea warfare activities brought about a wide-ranging study in 1950 at MIT by the CUW. The participants included well-known scientists and engineers from Bell Laboratories, California Institute of Technology, Carnegie Institution, Harvard, MIT, Marine Physical Laboratory, and the Scripps Oceanographic Institution. The comprehensive study called, Project Hartwell, addressed long-range defense against submarines.

For three months ending August 31, 1950, the group studied wide-ranging Navy problems related to the various aspects of overseas transport in a possibly unfriendly environment. This period also saw an expanding Korean War and with its requirements. The September 1950 Project Hartwell report suggested and recommended an extensive number of important measures to be pursued. It was intended that most of the Hartwell recommendations with adequate support could begin to be in service in two years. Significant effort by the Hartwell group was directed at protecting shipping against submarines and mines. 19 Regarding undersea surveillance, the Hartwell report findings included an immediate start of research to exploit the potential of low-frequency bottomed hydrophone arrays with multiple sites for triangulation to detect, identify, and track distant enemy submarines.

The Hartwell participants understood that there were unknown factors related to undersea surveillance and recommended an annual $10 million to develop an effective, long-range acoustic detection sensor system using bottomed hydrophone arrays. What would become a two-ocean surveillance system was gradually implemented. Commitment to what became SOSUS assured the Navy’s continuing, strong, and growing interest in oceanography. This system concept, because of its method of operation and locations, proffered resistance to destruction, foul weather, and ambient self-generated noise features not available at the time to other surveillance technologies.

American Telephone and Telephone Company (AT&T)

During 1949, the Navy’s ASW priorities regarding the enemy submarine threat were brought to the attention of industry. Dr. Mervin Kelly, then president of the Bell Telephone Laboratories of AT&T, met with CNO to discuss antisubmarine warfare. In October 1950 after the completion of Project Hartwell and its approval of quickly initiating steps to develop adequate ocean surveillance, Dr. Kelly offered the services of Bell Laboratories to the CNO.

In late December 1950, as a result of Dr. Kelly’s offer, ONR contracted with Western Electric, the engineering and manufacturing part of AT&T. The $1 million research and development contract, sponsored by ONR and Bureau of Ships (Buships), was to develop an undersea surveillance system based on long-range low sound propagation.

The overall effort evolved into several areas including: system design, engineering, deployment, shore station construction, hydrophone cable laying and the oceanographic research needed to understand long-range sound transmission in the sea. Caesar was the unclassified designation for the installation and production efforts. The research and development work by AT&T was designated Jezebel.

Commitment to undersea surveillance made it mandatory to broadly investigate propagation of sound in the sea and find answers to bathymetric questions such as depth and ocean con-tours. This part of the system development, called Michael, was under the purview of Columbia University Hudson Laboratories, Woods Hole Oceanographic Institute, Scripps Oceanographic Institute (SOI), and the Navy Hydrographic Office.

LOFAR (Low Frequency Analyzer and Recorder)
This device coming from the AT&T Bell Laboratory (BTL) became an important system component early in the surveillance program with the first unit delivered in May 195 I. AT&T adapted its recently-invented sound spectrograph, a tool for analyzing speech sounds, to analyze low-frequency underwater signals in near-real time. The output of LO FAR showed on paper readout the frequency of the signals picked up by the bottomed hydrophone arrays. Through the years that the system was in use, appropriate new technologies were invoked and provided significant system performance enhancement. As more SOSUS stations were placed in operation, a vast number of LOFAR analyzer/recorders were needed to accommodate the increasing number of hydrophones. Comments regarding the personnel needed to operate these stations and their unique abilities and equipment will be addressed later. Additional appreciation for the effectiveness of the LOF AR equipment was recognized as it was introduced to the Navy’s long-range maritime patrol aircraft (VP) and submarine communities.

First Test: Sandy Hook, New Jersey
This consisted of a series of experimental trials by the installation of undersea listening arrays off Sandy Hook, NJ. The experiment consisted of a cable and a few hydrophones installed in shallow water with the cable terminated in a building owned by the U.S. Army. Even with the high ambient noise due to the proximity to New York Harbor, range tests demonstrated the feasibility of surveillance and submarine detection.

Captain Joseph P. Kelly, USN
In May I 951 with the ongoing Korean War Lieutenant Kelly, a WWII naval officer and member of the Naval Reserve, was recalled and reported for duty in Washington. His prior experience included working at Westinghouse in Pittsburgh as an electrical engineer on large turbine generators and cable transmission systems from 1937 to 1942, when he was commissioned as an Ensign. His WWII experience included assignment as Maintenance Officer for magnetic loops and harbor defense mine fields in Panama. At the end of WWII, he continued his work at Westing-house.

In December 1951, he was interviewed by Rear Admiral Homer N. Wallen, Chief of the Bureau of Ships, who asked him, “What do you know about Jezebel?” His response was “What’s that?” the Admiral replied, “Welcome Aboard: you’re the new Project Officer.” This was the beginning of Joseph’s Kelly’s twenty-one year association with Oceanographic surveillance.

As SOSUS project manager, his diligent and unceasing efforts for more than two decades brought the nearly-global system to full operational status. Ultimately, system locations included the Atlantic and Gulf coast of the United States under the Caesar project. This was followed by surveillance covering the United States Pacific shelf from Vancouver to Baja California. Two arrays covered Soviet submarine Atlantic entry from northern Europe. Access for Soviet submarines from eastern Siberia was monitored with arrays from the southeastern tip of Japan, eastward parallel to the Kuriles and northeastern to the Aleutian Islands.

Test Site: Eleuthera, Bahamas
Lieutenant Kelly, as Buships Code 849 assigned to oversee the high priority project Jezebel, obtained permission from the British government to make a surveillance installation on the island of Eleuthera in the Bahamas. With assistance from a British cable layer, underwater cable and six hydrophones were installed, three in 40 feet of water, two at 960 feet, and one at 1000 feet and in addition, the first deep-water array with a 40 hydrophone linear array (1000 feet long at 240 fathoms). The long array maximized the signal gain at the low frequencies of interest. Narrow band signal analysis maximized processing gain. With the shore-based equipment in place, the system was operational by January 1952.

A Decisive Test
On April 29, 1952, scientists from Bell Laboratories demonstrated their LOFAR passive detection system to a group of flag officers at Eleuthera. A U.S. snorkel-equipped submarine acting as a target maneuvered offshore and was given instructions to change course, speed, and depth. Final instructions required the submarine to open range and make a box maneuver every 25 miles to provide checkpoints. Positive detections of the submarine were achieved and paper output from the LOFAR (Lofargrams) convinced those present that the detections were real. In Washington steps were taken to make Project Caesar happen. In 1952, Joseph Kelly was appointed Lieutenant Commander

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