Origins of SOSUS
The modern era of sonar began in the 1920’s when there was a steady advance in applying underwater sound to practical needs. During this period, depth sounding by ships was developed and echo ranging on submarine targets received a great impetus from advances in electronics. Thomas Edison and other luminaries became involved in research on passive listening devices. Numerous scientists explored the physics and oceanography on which later work would be based.
Work began in earnest at the start of World War II, when German submarines torpedoed Navy-escorted convoys. In the darkest days, 120 U-boats were operating in the Atlantic. Wolf packs frequently outnumbered escort ships by a factor of two-to-one. At one stage our ships were being sunk faster than we could replace them, and some of the sinkings occurred within sight of our coasts. Keeping supply lines open for thousands of miles was agonizingly difficult.
The mobilization of the Nation’s resources turned the tide – all the shipbuilding skill, training ingenuity, and scientific effort that could be mustered. Without sonar, the U-boat threat could never have been contained. But the toll by the end of the war was enormous: 4,733 allied ships, 966 enemy boats, and a great loss of human life. It was a stiff price to pay to maintain supply lines.
In the waning days of the conflict, the Germans developed the Snorkel submarine – a true submersible that could operate under diesel power at periscope depth. Its designers claimed cruising ranges of 20,000 miles at speeds approaching 25 knots. The Snorkel submarine was a weapon that far exceeded its predecessors; thus, a new challenge had been presented to the antisubmarine warfare community.
In the 1940’s, even as the world was at war, experiments were conducted at the Woods Hole Oceanographic Institution and elsewhere which demonstrated the long-range propagation of sound in the ocean at low frequencies. This phenomenon is associated with the vertical sound speed structure and, in particular, the existence of a deep sound channel in most ocean areas. A system for locating fliers downed at sea was one of the first applications to be considered. The system was SOFAR for SOund Fixing And Ranging. It consisted of three or more hydrophone configurations placed near the sound channel axis with sufficient horizontal separation to obtain an accurate triangulation fix on the signal from a small explosive charge released by the flier. Several SOFAR stations were established, but were never used as intended. Instead, they became important sites for continuing research on the characteristics of sound transmission and noise.
In 1946, True Magazine published a story on how the deep sound channel might be exploited for the passive detection of submarines. That same year, Dr. Glenn Camp of the Operations Evaluation Group in Chief of Naval Operations described the existence of low-frequency distinct line components in the radiated spectrum of diesel submarines. For classification of the signal he suggested the use of a visual speed analyzer developed by Dr. Ralph K. Potter of the Bell Telephone Laboratories. Dr. Camp promoted his idea, but nobody listened; he was ahead of his time.
Early in 1949, the Naval Research Laboratory reported submarine detection ranges of 10-15 NM in tests using SOFAR hydrophones off Point Sur, California. By the end of the year, ranges of several hundred miles had been achieved. That same year a SOFAR station was established at Bermuda by Dr. Maurice Ewing, a world-famous oceanographer and one of the great contributors to our knowledge of underwater sound.
During this period the Soviet Union set out to create its own political and economic sphere, independent of the West. The Russians mobilized their scientific resources to develop first the atomic bomb and then the hydrogen bomb. The danger of nuclear war became a central fact of modern life and a furious arms race began.
On the seas the admitted goal of Soviet admirals was to achieve naval supremacy, to use the navy as a key element of Soviet global strategy. Great emphasis was placed on completely modernizing naval armaments, especially the submarine force, which became the largest in the world. Our military leaders and analysts viewed the threat posed to the Free World with alarm.
In 1949, the Committee on Undersea Warfare of the National Research Council informed industry about the state of antisubmarine warfare and polled organizations on what might be done to meet the threat. Dr. Mervin J. Kelly, then president of Bell Telephone Laboratories, was so impressed with the importance of the problem that he called on Admiral Sherman, Chief of Naval Operations, and discussed antisubmarine warfare in detail. Considered basic to national survival was the ability to use the high seas to transport men and materiel in face of the threat posed by enemy submarines.
In a letter dated January 23, 1950, to Admiral C. B. Momsen, Assistant Chief of Naval Operations, the Committee on Undersea Warfare recommended that a long-term program be formulated to meet the submarine threat. Subsequently, Admiral Momsen and Admiral Solberg, Chief of Naval Research, met with Dr. Kelly and Dr. James B. Fisk, Dr. Kelly’s assistant and later his successor, together with Dr. Julius Stratton, provost of MIT. It was decided that a broad study should be conducted that summer on the security of overseas transport. Professor Zacharias of MIT chaired the study and Commander Groverman of Office of Naval Research was assigned as liaison officer. The code name Hartwell was adopted and the participants became known as the Hartwell Committee.
At about the same time, the Fifth Undersea Symposium was held in Washington, D.C. At that gathering, Professor Ted Hunt of Harvard, a renowned acoustician and director of the Harvard Acoustics Laboratory that contributed so much to sonar during World War II, presented a momentous proposal outlining new concepts in underwater detection. He suggested the exploitation of the deep sound channel to achieve very long ranges, concentration on frequencies below 500 Hz, the construction of arrays at least 20 wavelengths long and oriented vertically to delineate ray paths, and the use of magnetic recorders for post-analysis of data.
Also at that time Submarine Development Group Two at New London (the antecedent of the Underwater Sound Laboratory and NUSC), announced detections of diesel submarines using 1/8th octave filters. They found low-frequency sounds between 25 and 200 Hz with peaks at 100 Hz. Investigators at Woods Hole concluded that the line components in the spectrum were highly stable, and that, consequently, the filter bandwidth could be substantially reduced to improve the signal-to-noise ratio.
The Hartwell Committee delivered its report in the fall and recommended the development of nuclear-powered submarines. It suggested the marriage of missiles with submarines, which led to Polaris. It urged the construction of fast, modern transport ships. It also targeted the detection of submarines using real time spectral analysis of radiated sound energy as holding most promise for the future of antisubmarine warfare. Its specific recommendations included the following:
a. The real time narrow band analysis of radiated sound;
b. The use of low-frequency noise for underwater communication or navigation;
c. The possible reduction of submarine-radiated signals by feeding back sound in phase opposition. It was believed that low-frequency spectrum analysis would do to the detection of the submarine threat what the magnetron had done for radar in 1939.
In October of 1950 Dr. Kelly called on Admiral Sherman once again and offered the services of Bell Laboratories. Admiral Sherman with a letter which stated "I have directed Admiral Solberg, Chief of Naval Research, to proceed with arrangements with Bell Telephone Laboratories to institute a program of research and development in the field of low-frequency sonar." Bell Laboratories was already at work adapting Dr. Potter’s visual speech analyzer to the task before Dr. Kelly’s Washington visit.
Western Electric Company (WECo) wrote a proposal and went to Washington on the 29th of October with a letter of intent. A contract was signed a month later between ONR and WECo for the R&D effort. The amount was for one million dollars.
In the months that followed, rapid progress was made in confirming that prominent low-frequency components were present in the submarine’s spectrum and that the sounds were of sufficient intensity to offer exceptional potential for long-range detection. At Sandy Hook, New Jersey, a small experimental system comprising a cable and a few hydrophones was installed in shallow water. The cable was terminated in a building owned by the U.S. Army. Despite high ambient noise due to the heavy shipping in the area, rudimentary range tests were conducted which demonstrated the feasibility of surveillance.
The first report on the project, which came to be called Jezebel, outlined the parameters for a Low-Frequency Analyzer and Recorder, or LOFAR. Bell Laboratories presented a working model of the spectrum analyzer with an analysis band of 1-1/2 Hz, operating in real time. Schemes were described for hydrophones, cables, delay lines and networks for simultaneously presenting multiple beams to achieve wide azimuth coverage. The first brass board model of a lofar was delivered in May 1951.
In July 1951, negotiations were completed with the British to acquire a seashore site at Eleuthera in the Bahamas. Six hydrophones were installed – three in 40 feet of water, two at 960 feet, and one at 1,000 feet. The first deep-water array was also installed off Eleuthera. It was a 40-hydrophone linear array, 1000 feet long, installed in 240 fathoms of water.
Early in 1952, two important events occurred. In January Captain Joseph P. Kelly (then Lieutenant Kelly) became project manager of Jezebel. And on the 29th of April, a group of flag officers visited Eleuthera. An U. S. submarine maneuvering offshore was given instructions to change course, speed, and depth. Final instructions called for the submarine to open range and make a box maneuver every 25 miles to give checkpoints. The admirals didn’t wait. They had seen the lofargrams and were convinced that the detections were real. They headed back to Washington to make Project Caesar happen. Besides, the National Research Council had declared lofar a breakthrough.
The initial Caesar contract directed Bell Laboratories to undertake a program aimed at the manufacture and installation of equipment for long-range detection and classification. The development was to be carried on concurrently with the research program. A few months later, in June of 1952, CNO directed the Bureau of Ships to procure six stations. The brakes were off and Caesar was on its way.
The CNO letter suggested the following sites: Sable Island, Cape Hatteras, Bermuda (two arrays), Eleuthera, and Culebra, Puerto Rico. One week later CINCPACFLT wrote a letter to CNO saying they wanted to be kept advised of progress and offering a plan for wiring up the Pacific. At the end of June three major contracts had been put into effect – one for equipment, one for installation, and a third for the construction or expansion of a cable plant. And, for the first time, the low-frequency passive detection system was called SOSUS, for SOund SUrveillance System.
Events followed in rapid succession thereafter. Wartime rules for procurement were still in effect, and, action followed in short order. The Simplex Cable Company was expanded to manufacture Caesar cables. The U. S. Navy Hydrographic Office set up a survey group and assigned three ships to undertake bathymetric surveys. The Maritime Administration released the cable ship Bullard to the Navy, who rechristened her the Neptune. New cable drums 15 feet in diameter and bow sheaves 12 feet across were installed, the largest in existence. The Albert J. Meyer was added to the fleet. Two lofar units were sent to England to analyze submarine signatures obtained by the British.
In September of 1952, CNO increased the number of stations from six to nine, and changed the locations of several. The new plan called for sites at Sable Island, Nantucket, Cape May, Cape Hatteras, Bermuda, San Salvador, Grand Turk, and Ramey Field, Puerto Rico. Three more stations were added at Barbuda, Barbados, and Newfoundland in January 1954. Pacific expansion came in May 1954, when ten more stations were planned, six on the West Coast. Not everything went without a hitch. An array and cable were installed in the summer of 1954 off Grand Turk. Because of the low resolving power of fathometers in use at that time, the array was laid in a crack on the surface of a seamount and to be abandoned for later relocation. When the problem was reported, an officer asked Joe Kelly from CNO if the cable ship had "used a lead line." Joe quietly replied that the ship had only been working in a thousand fathoms of water. Much was new and strange in those days, even to Navy personnel.
Target IOC dates were set for the NavFacs, one a month beginning in the fall of 1954. Ramey was the first to come on the air, in November, roughly one month late. The time between the Hartwell report and the first operational system was a little under four years.
Research and development work continued as other stations came into being. Major changes were made in bringing signals back to shore – first with multi-pair cable, later with coaxial transmission systems.
In reflecting on the early years of SOSUS, what is most striking is how much was accomplished in remarkably short time. Certainly a major factor was serendipitous confluence of events – the discovery that low-frequency sounds could travel great distances in the ocean, the realization that submarines radiate identifiable low-frequency energy, and the pioneering work at Bell Laboratories on visual speech analysis. Ease of contracting was also an important element. The Navy’s resolve to conduct undersea surveillance was crucial. The commitment of WECo and Bell Laboratories and their decision to assign some of their best people to the project were of considerable consequence.
[Data certified UNCLASSIFIED by DoD/DoN and IUSS Authorities]