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Methods using sound in the sea as a tool for underwater detection as a navigational aid and enemy submarine finder expanded considerably throughout the 20th Century. History shows the Boston based Submarine Signal Company as a pioneer equipment developer manufacturer and implementer of what later became to be known by 1943 as sonar. It should not be over-looked that Submarine Signal during the 1930s and ’40s also had involvement in the developing field of radar and during WW II with the manufacture of thousands of marine radar sets and radar fire control apparatus as well as continuing extensive sonar development and manufacturing. In 1946, Raytheon purchased the Company. As a division of Raytheon, today it is now known as the Naval and Maritime Integrated Systems. In its second century, this part of Raytheon continues to design, develop and build sonar equipment for surface ships, submarines and ASW equipment for helicopters. This essay recalls some of the first half century of the story.

A New Century

As the first days of the 20lh Century unfolded, two ongoing important maritime pursuits were moving along separate paths that merged into one by 1920. Toward the end of the 1800s, an interest began in developing commercial undersea sound devices to enhance the safety of merchant shipping by alerting ships to the presence of rocky coasts. With the draft of steel ships increasing, warning of natural hazards and the presence of shipwrecks along coasts became important. Knowledge of the ocean bottom related to laying underwater cables, telegraph, telephone, and power, was an additional need. Because of the vagaries of sound in air, sirens and foghorns as warning devices for shipping were limited. Ocean depth determination methods at that time were ponderous and time consuming. Interest in sound as a way to determine depth also began to receive new attention.

The other maritime interest that became predominant came from the April 1900, United States Navy purchase of John P. Holland’s HOLLAND VI, the first practical submarine. By 1914 there were 400 submarines in the world’s navies; by 1982, 1000. The innovative submarine required a way to navigate underwater and to find its targets; its opponents wanted to find the submarine and destroy it. This essay is an abridged version of how the Submarine Signal Company contributed to solving navigation and detection requirements during the first part of the 20 •h century. The Company’s engineers’ commitment to continued progress during the remainder of the century is another essay.

For several years starting in 1898, Arthur J. Mundy, Elisha Gray (telephone inventor and one of the founders of the Western Electric Company), and Joshua B. Millet conducted experiments concerned with the use of a sea buoy with an underwater bell and a receiving microphone located on a ship to warn of hazards. Mundy’s home on Cape Ann, Massachusetts, on the north shore was the site of the initial work. The project benefitted from Gray’s technique for waterproofing telephone transmitters in developing the underwater equipment. Gray called the underwater micro-phone a “hydrophone.” It consisted of a metal case with a thick metal diaphragm, which was attached to a carbon button micro-phone. Prior to Gray’s microphone and telephone headsets, a stethoscope-like receiver was used.

Submarine Signal Company Begins

In 1901, Mundy, Gray, Millet, E. C. Wood and others established the Submarine Signal Company to pursue the development, sale and installation of underwater bell systems. Working with these systems added new knowledge of the behavior of sound in the sea and how to have equipment meet the demands of that environment. It was observed that microphones on the ship’s hull picked up the ships own noise and prevented good reception. In the years 1898-1902, it has been estimated that about $80,000 was invested to come up with a way to dispense with a microphone on the outside of the ship’s hull for reception of the underwater bell signals.

Aiding at-sea navigation, ocean depth determination and underwater cable laying led to using sound underwater in new ways to achieve these goals. As in the development of most technologies, there was no straight-line path from need to implementation.

Underwater Bells

Lightships were the first to be instrumented with underwater bells. Some bells were operated with steam others with compressed air. In 1903, the first of the Submarine Signal Company’s bells was installed in Boston Harbor on Lightship 54. On sea buoys, wave action coupled with a spring mechanism activated some underwater bells later. Ranges were typically about eight to ten miles. Electrical bell operation with cables from the shore provided further location flexibility where it was not feasible to locate a lightship or a buoy. In some instances, the signal from the bell was coded for identification.

By the end of 1903, four lightships were equipped with underwater bells. The bells automatically struck the code number (dots) to identify the lightship to the ship equipped with Company’s receiving apparatus. Several years later, the United States and British Admiralty were cognizant of the reliability of the pneumatic submarine bell. The British Submarine Signal Company covered the European equipment sales and service. Underwater receivers were not sold to commercial shipping. They were leased, and the Submarine Signal Company provided servicing and modernization of the equipment.

In April 1905 at a meeting of the Institute of Naval Architects, J. B. Millet of the Submarine Signal Company presented a paper that discussed the successful operation and wide use of submarine bells. At the meeting, Captain Reginald Bacon RN, first Inspecting Captain of Submarines and head of the embryonic British Submarine Service, spoke of the possibility of detecting submarines by the noise of their engines and observed that with electrical propulsion underwater, the noise was very slight.


As mentioned above, experimental work indicated that micro-phones located on the hulls of ships picked up the ship’s machinery noise as well as the signal from the bell. In the case of weak signals, this was unacceptable. It was learned that this could be avoided by streaming the microphone away from the ship’s noise on a towed platform. Although workable, this method was awkward for commercial use, and other methods were pursued.

Submarine Signal Company founders Joshua B. Millet and Arthur J. Mundy developed a practical method for eliminating the ships self noise. Most of the ship’s noises were reduced by hanging a waterproofed microphone in each of two tanks filled with a chemical solution denser than water. The tanks were about 16 inches square and 18 inches deep. With the tank secured against the side of the ship in the port and starboard fore peak, it was not necessary to cut a hole in the side of the ship.’ The tanks were bolted to the ship’s framework and sealed firmly to the ship’s side by rubber facing. Signals coming from outside the hull passed through to the microphones while the own ship’s noise also coupled to the microphone was reduced. The submerged warning bells were designed to resonate at 1215 Hz submerged.

Outputs from the microphones were fed to a pair of telephone receivers mounted on the bridge. A switch allowed the listener to use either the port or starboard microphone. A complete second set of receiving equipment was installed to provide reliability. A bearing of the sound waves from the bell could be found by balancing the level of the signals picked up by the port and starboard microphones through adjusting the ship’s course.


Three Big German Ships Fitted with New Apparatus.


New York Times June S, 1905

On June 5, 1905, the New York Times reported about submarine signaling with generous praise. The systems advantages were extolled by the officers of the North German Lloyd liner WILHELM DE GROSSE, recently arrived from Germany in New York. In addition, other German Lloyd Ocean liners KAISER WILHELM II and KRONPRINZ WILHELM were similarly equipped.

When under the conditions of fog and mist and approaching land, the liner’s watch officers placed high value on the system. With each underwater bell having an identifying numerical code, accurate information about location in addition to providing a warning was provided to a ship proceeding under conditions of poor visibility. En route to New York from Germany, as the liner WILHELM DE GROSSE neared the coast a signal of six rings followed by an additional six. identified the presence of the NANTUCKET lightship. In a like manner, other lightships along the coast were identified: FIRE ISLAND with 6-8 bells and SANDY HOOK with 5-1. On departure from Germany, four miles from the mouth of the River Weser the local lightship provided a signal.

The Times also pointed out “Great Britain, Germany, and Italy have taken up the system, which they are installing along their coasts, while in Canada the St. Lawrence is guarded with the bells from the Atlantic to Quebec.”

In 1906, Submarine Signal Company bells received United States Lighthouse Service approval and steam-operated bells were placed aboard several lightships in Massachusetts’s waters. Circa 1918, 52 United States lightships and 9 buoys were equipped with the bells. After improvements, ranges of the order of 10 miles were typical. A quote by George R. Putnam, Commissioner of US Lighthouse Service (1910-1935) is of interest: “Sound from submarine bells is transmitted through the water more uniformly and effectively than it is through the air from aerial signal.”

Acceptance of Submarine Signal’s systems using underwater bells was initially difficult but was fully established by 1912 in America and Europe. At that time, worldwide 135 of the alerting system bells were installed. More than 900 ships were equipped with the receiving equipment. Further encouragement came from the U.S. Shipping Board directive that all steel ships constructed by the Board be equipped with Submarine Signal Receiving Apparatus. It should be noted that strides made in radio transmission and reception (radio direction finding) pointed to other methods warning vessels of danger which competed with the underwater bell systems.

Submarine Signal Company

Submarine Bell Systems World Wide 1912

Australia Argentina Belgium Brazil Canada
Chile China Denmark France Germany
Great Britain Greece Holland Italy Japan
New Zealand Norway Portugal Romania Russia
Spain Sweden United States

Industrial interest in the evolving technology should not be overlooked as a factor in seeking and improving detection of sounds in the sea. In parallel, the vested interest of the world’s navies to seek solutions to enemy submarine detection provided a developing and long-term partnership with industry in this pursuit. In addition, the sea itself, an obstinate medium, became the source of a myriad of related questions and problems demanding answers.

With the arrival, rapid growth, and improvement of practical submarines during the 20th century, sound in the sea gradually became entwined with the world’s navies of surface ships and submarines. The April 12,1912 Titanic iceberg disaster stimulated renewed strong interest in underwater sound techniques for obstacle avoidance. Growing naval interest in submarine detection and commercial shipping concerns about improving safety at sea by the use of underwater sound shared a common goal. During World War I (1914-1918), there was little progress in increasing the number of submarine signal stations. After the Armistice in 1918, the demand from shipping for more submarine signal stations increased, with international support from the lighthouse services worldwide.

Successful use of underwater sound by surface ships hunting submarines became an elusive goal. It was not until the extensive and well-timed use by Germany’s U-boats of a cours de guerre tactic starting in 1914 and continuing throughout World War I that increased attention was paid to the importance of underwater acoustics as a tool for antisubmarine warfare (ASW). At the same time, sound detection developed as a pro-submarine tool when submarines were submerged and operating blind in the opaque ocean.

Although the emphasis for the development of these systems was heavily practical, overall knowledge of the sea and the transmission of sound grew. In 1919, more than 150 bells were in operation. The 1920 count of Submarine Signal Company installations included 2,161 merchant ships and 1,026 naval vessels. Besides merchant ships and navies, fast passenger ferries operating from England to the coast of Europe used the submarine bells to check the boat’s positions and as late as 1930 found the navigation method in daily use.

Origins of Echo Ranging

In the new century, echo ranging with rudimentary detection and distance finding features for underwater detection of objects using sound waves began with the research of two men, one working in England and the other in the United States.

Lewis F. Richardson

Five days after the tragic sinking of TITANIC, British physicist and meteorologist Lewis F. Richardson filed a patent for echo ranging with airborne sound. “An ingenious feature of his scheme was suggestion for discriminating between the transmitted signal and the echo by using a frequency-selective receiver detuned from the transmitting frequency by just the amount required to compen-sate for the Doppler shift arising from motion of the echo-ranging vessel. “7 He followed a month later with a second British patent application for the underwater equivalent,” … detecting the presence of large objectives underwater by means of the echo of compressional waves … ” He specified the frequency of the source should be about 5000 Hz or higher.

Reginald A. Fessenden

From 1910 to 1921, Fessenden a well-known engineer, inventor and successful radio pioneer with a lifetime accumulation of 300 patents, was a consultant to the Submarine Signal Company. Fessenden’s objective at Submarine Signal was to develop a more efficient underwater sound source that could be modulated into the dots and dashes of the Morse Code. 8 This further refinement of underwater signaling would broaden the Submarine Signal Company’s product line. As a young researcher, he worked with Thomas Edison. The widely-used amplitude modulation used in radiotelephony and broadcasting was one of Fessenden’s accom-plishments. He is probably best remembered for his 1906 radio voice broadcasts.

During his first year with the Company, Fessenden developed an oscillator that created high-energy sound waves in the water at 540 Hz. The oscillator, in addition to sending sound waves, was capable of receiving and could be used in place of a microphone to change the received sound waves into electrical impulses. The oscillator could be keyed with a telegraph key, and Morse code could be sent at increased speed and at five times the distance of the equivalent underwater bell system.

Fessenden filed for a United States patent in 1913 related to the detection of underwater objects using echo ranging. This included a moving-coil transducer operating at low frequencies and planned for signaling and echo ranging. In some instances it was used as transmitter in conjunction with a hydrophone receiver. Other features of the oscillator were noted “Later analysis showed this device to be very efficient-that is, between forty and fifty percent-with a power in the water of about two kilowatts. “9 The electroacoustic device, capable of transmitting and receiving acoustic energy in the water was referred to as the Fessenden Oscillator and sometimes identified as the first true underwater transducer. The patent was granted in 1916.

When testing the oscillator for transmitting and receiving code, it was observed that reflected waves (echoes) interfered with signal reception. Initially, it was not initially recognized that echoes horizontal (from the target) and vertical (from the ocean bottom) could be used for ranging. Fessenden’ s patent aimed at the distance between the oscillator and the reflecting surface.

The concepts conveyed in his patents and the at-sea successful demonstration at sea of detection by echo ranging by Fessenden on April 27, 1914, provided stimulus for this detection method. Both Fessenden and Richardson were interested in underwater obstacle avoidance.

Fessenden’s first sound oscillator was an air-backed electro-dynamic driven clamped-edge circular plate a half inch thick. Weighing about 1200 pounds with a 30″ diameter 1/2” thick diaphragm it was designed to operate at 540 Hz () .. =8.9 feet). The motor generator delivered 4-1/2 kilowatts at 180 volts. The one way range was typically 4-5 miles, with maximum ranges of 30 miles reported. These oscillators found use in World War I. “By June 1927, all U.S. submarines had 540-Hz oscillators … ” 11 Modified versions of the oscillators continued as research low frequency (500, 1000 Hz) sound projectors until the mid-201h century.

A test of the oscillator was made in January 1914 aboard two ocean going tugs. Tug SUSIE D with the oscillator aboard anchored at the Boston lightship and towered the oscillator into the sea. Fessenden and Submarine Signal engineers aboard the tug NEPONSET received the signals out to a distance of 31 miles in the vicinity of Cape Race at the tip of Cape Cod. Inclement weather in the form of a snowstorm terminated the demonstration. In another January test in the Boston Harbor, underwater communication was first shown by using a Morse code carrier to modulate the oscillator, thus demonstrating a means of ship-submarine acoustic communication.

Royal Navy and Fessenden’s Oscillators

As a result of the success of the sea tests of Fessenden’s apparatus, built by Submarine Signal Company described above, the Consul in Boston advised the Admiralty of the results. Later, trials of the equipment were successfully held in England in Portsmouth Harbor. Next, equipment was procured for installation on ten H class submarines and 24 others under construction. Shore installations were made at Dover and Horse Sands Fort, Ports-mouth to control the submarines in the area. The oscitlator output was modulated with a Morse key. On the British submarines it was noted that the steel deck would vibrate when transmitting and produce a tickling sensation in the feet. The normal range achieved for passing signals between submerged submarines was about 3 miles, this was sometimes exceeded (93 miles was once recorded off the North China Coast).

The article referenced in footnote 12 describes how the distance between two submarines could be determined. “The distance between two submerged submarines could be measured by stop watch, the originator transmitting F and starting the watch on the last dot, the receiving boat then transmitting when it heard the last dot, and originator making a final F on the last dot of the other boat’s transmission. Each could then work out the distance apart from a ready reckoner equating time with distance. The result either pleased the officer of the watch, or frightened him to death!!”

Echoes from an Iceberg

For a further demonstration, in March 1914 at Halifax, Nova Scotia, Fessenden’s equipment was installed on board the United States Revenue Cutter MIAMI. At that time, the Cutter was assigned to the first International Iceberg Patrol. In 1912 follow-ing the loss of the liner TITANIC after it collided with an iceberg, there was considerable interest in determining the presence of icebergs in or near the steamer lanes. The equipment consisted of Fessenden’ s oscillator suspended in the water from the side of the 190-foot MIAMI. The oscillator was capable of performing as both a sending and receiving device. Reception was also sup-ported by a Submarine Signal Company hydrophone.

An iceberg 450 foot long and 130 foot high was sighted on April 27, 1914 on the Grand Banks, off Newfoundland, Canada. Fessenden’s oscillator was directed at the iceberg and for 3 hours horizontal echoes were received from the iceberg at ranges of 112 mile, 1 mile out to 2-112 miles. The distance traveled was determined by sending oscillator signals and timing their return by means of a stopwatch. Some echoes came from other icebergs. Additional echoes arriving at constant intervals were found to be from the ocean bottom and provided depth readings.

After the test, a radio telegram was sent to the Submarine Signal Company’s Boston Office:

“First test today, bottom one mile. Berg two miles. Results good. Heard in wardroom also. Test stopped by bad weather.”

In 1915, the oscillator was even tested at 100 kHz. The Fessenden oscillator models (ca. 500, 1000, and 3000 Hz) were so successful that they were even used until, and during, World War II for sonar and mine detection purposes. Despite these landmark achievements, at present no oscillators are known to exist, and no modern acoustic measurements have ever been made to establish the acoustical performance.

Time for the signal to reach the target and return was measured on a stopwatch and the distance to the iceberg determined. Echoes were received out to a distance of two miles. Direction of the underwater object could not be determined with the equipment. It was also noted that with the icebergs salinity equal to that of the seawater, a portion of the sound directed at the berg was absorbed. The same year the Marine Journal reported that it is possible with Fessenden’s device to use the Morse code in telegraphy and also to telephone through the water. At the beginning of 1915, International Marine Engineering reported that the oscillator had been heard at a distance of 30 miles.

Using the oscillator and the echo, Fessenden also made ocean depth determinations. He referred to his sound system as Iceberg Detector and Echo Depth Sounder. In April 1914, Fessenden applied for a related patent called “Method for measuring distance” granted in February 1917. It appears that by 1922, Fessenden while at Submarine Signal progressed to using the cathode ray tube and developed submarine detection devices based on pulsed acoustic waves.

Bells and the Submarine

Submarine Signal Company bells were installed on both United States and British submarines. A comment in the Naval Institute in 1915 stated that many submarines were fitted with both subma-rine bells and receiving microphone.

“In the case of submarine boats. however. owing to the fact that the bell is hung in the peiforated superstructure, and its sound is transmitted directly to the open sea. it is entirely practical to signal from one to the other. ”

Journal of American Society of Naval Engineers, Vol. XXI, No. 2, May 1909, “Submarine Signaling”, p. 453-457.

“Before ascent is made, it is practice to listen in on the submarine bell receivers for the noises made by the propel-lers of passing vessels.”

“GRAYLING directed maneuvering of NARWHAL, communicating by means of submarine bell apparatus. ” Scientific American, “The Modern Submarine”, LT D.C. Bing-ham, Dec. 9, 1911.

“All modem submarines are.fitted with devices which enable the commanders of submarines to communicate with each other when running under water. One of these outfits consists of a signal bell and a powerful receiver with which sounds may be transmitted and heard. ”

Simon Lake, The Submarine in War and Peace , Philadelphia, Lippincott, 118, pg. 27

In the following years, Fessenden’s submarine oscillators found wide applications in both the military and commercial area. Data on a Fessenden submarine oscillator placed in operation on the Nantucket Lightship in 1923 produced the data in the following table.

Analysis of Ship’s Reports of Distance Observations of Submarine Signals from Nantucket Lightship October 1923-January 1, 1929 (846 reports

Signals Heard Least Distance (miles) Number of Reports % of Total Re-ports
5 765 89.4
10 488 57.0
15 285 33.33
20 178 20.8
25 107 12.5

Under adverse conditions, average distance for foghorn reception is about 4 miles and under favorable conditions 8 miles.

Later in the 1920s, a Fathometer based on Fessenden’s investigations became a Submarine Signal Company product. In 1929, practically all U.S. Hydrographic Office ships engaged in deep-sea soundings used sound depth apparatus of the Fessenden type, developed by the Submarine Signal Corporation.” Scientific American’s Gold Medal for 1929 was awarded to Fessenden for the fathometer, which could determine the depth of water under a ship’s hull.

An Observation and a Need

A July/August 1915 Naval Institute Proceedings commentary .. Submarine Signaling” points out the dilemma of the submarine captain. Fog confounds the surface ship captain. The submarine captain, submerged and with limited opportunity to use the periscope, operates in an environment equivalent to perpetual dense fog. Further discussion relates the pros and cons of underwater bell signaling. A comment is made that proper exploitation of the Fessenden underwater oscillator could offer solutions to underwater navigation.

World War I Technology

In the United States, almost two years before it entered the War, the sinking of LUSITANIA by a submarine torpedo in 1915 stimulated members of the scientific community to offer their services in the pursuit of antisubmarine warfare methods and techniques. This coming together of the scientific community and the military for joint war effort did not stop at the end of World War I. Civilian scientists and military personnel working together occasionally presented difficult situations. As the war went on, in addition to Fessenden’ s oscillator, other approaches for detecting acoustic waves came almost directly from the laboratory to sea test.

U.S. Navy forces, submarines and destroyers, operating off Pensacola, Florida, during January, February, and March 1917 conducted tests and investigations of all prewar-available Jistening devices, which were those of the Submarine Signalling Company. The object of the tests was to determine the detection range of these devices under different service conditions. Submerged submarines listened to surface vessels of different types as well as to other submarines. Tests included the detection of submarines by surface craft. Results of the operations pointed out that the submarine was a better listening platform than the surface craft and that with the existing equipment, the probability of successfully detecting submerged submarines was remote. Specifying the location of the submarine was an additional problem.

Great Britain started submarine detection efforts in 1915. At that time, initial British investigations included equipping surface ships with prewar Submarine Signal Company hull mounted port and starboard hydrophones}9 By April 1917, Nobel Laureate Sir Ernest Rutherford, and others had two years of research and developing submarine detection devices using sound and meeting with some success. Eventually in Great Britain there were 31 British anti-submarine research centers, with 27 of the centers dedicated to some aspect of developing and implementing equipment to detect submarines using acoustics. Development of equipment that could pick up propeller noises and detect and locate enemy submarines and surface craft was of the highest priority in England.

Soon after the United States declared war against Germany, Rutherford came to United States with a contingent of ASW scientists and engineers from England and France. Meetings and technical exchanges were held in eastern cities and at university and industrial laboratories during the period from May 19 to July 9, 1917. In May a one-week conference was held in Washington, DC with 50 scientists.

Information exchanged included the British detection devices. Discussions also involved the results of the distinguished French scientist Paul Langevin’s successful investigations of the piezoelec-tric properties of quartz as an ultrasonic (150 kHz) transducer. At the ten primary United States ASW research centers established in 1917 and 1918 during WW I, investigations focused on piezoelectricity (quartz, Rochelle salt) and ultrasonics at seven of the centers. In the Post WWI period and beyond, piezoelectric transducers predominated. By the late 1950s, barium titanate, a synthetic material with piezoelectric propenies replaced natural materials in many designs.

The vacuum tube amplifier invented in 1907 gradually became an imponant tool in acoustics. Previous to the war, all vacuum tubes were strictly a laboratory proposition impossible to produce in quantity and of an almost prohibitive cost. By 1917, with a vigorous wanime effon, vacuum tubes became available and at a more reasonable cost. However, immediate solutions through the war years frequently made use of the human ear augmented with horns and tubes able to compete successfully with the available mechanical devices for detecting sounds such as the recording galvanometer.

Submarine Signal Company at Nahant, Massachusetts

As relations with Germany deteriorated, the Naval Consulting Board (NCB) established in 1915 held a meeting to discuss defense measures on February 10, 1917 at the Engineering Societies Building in New York. At this meeting the NCB, headed by Thomas Alva Edison, created a Special Problems Committee with a Subcommittee on Submarine Detection by Sound. The following day the New York Times reported an offer to the NCB made by meeting attendee H. J. W. Fay. Second Vice President of the Submarine Signal Company: ” … Company is ready to place its laboratories and all of its facilities at the command of the board in the event they are needed.” At this time, the U.S. Navy had no equipment to even detect the presence of an enemy submarine, let alone its location.

A week later, the NCB invited H. J. W. Fay to discuss submarine signaling and detection. This was followed later in Boston by a demonstration of the Company’s sound detection equipment. By letter on February 28, Fay requested authorization from the Chairman of NCB to obtain land to build a test station for submarine detection investigations near Boston. The NCB endorsed Fay’s letter, and Secretary of the Navy Daniels acknowl-edged Fay’s request. A site was found at Nahant, Massachusetts, on private land at East Point bordering on the Atlantic. Submarine Signal Company, General Electric Company and Western Electric Company pooled their resources and at their own expense constructed the test station. At the time, General Electric was already engaged in some research for the Navy in communications and submarine detection. Presently, engineers from the American Telephone and Telegraph Company were also at Nahant. 18 Submarine Signal Company furnished the buildings, the power plant and the oscillators. 19 The Nahant Experimental Station on April 6, the day before the declaration of war against Germany, conducted underwater sound experiments. The Station remained in operation for 20 months, disbanding in the beginning of 1919.

Nahant, a few miles nonh and east of Boston, is on a narrow peninsula consisting of several causeways jutting out into the Atlantic. The test station at the most eastern point provided an efficient location for researching and conducting experiments in the offshore waters. At Nahant, the first problem planned by the Western Electric Company was to determine the nature of the sounds produced by vessels and the distances at which they could be heard. Available apparatus for this work included using the Fessenden Oscillator for sending and receiving sound signals. Incorporating a pilotron tube (an early vacuum tube amplifier) recently invented by General Electric scientist Irving Langmuir, it was possible for the first time to detect movements of ships at distances of many miles. Langmuir became a Nobel Laureate in 1932.

Nahant Experimental Station Submarine Detectors

With the scientific and technological talents of the companies plus manufacturing capability, a series of detection devices were created, tested, installed and used during the twenty months of test station operation. Early investigations included consideration of Fessenden’s system for submarine detection. This concept did not meet with acceptance and was dropped. Research moved in the direction of passive detection and some of the various best effort detectors continued in use until the 1930s.


By the fall of 1917, the Nahant group developed the listening device known as the C-tube. Earlier on 21 August, in less than four months from the start of the investigations, an experimental system was ready for test. An accounting of this test demonstrates the early success as well as a practical approach to a complex requirement, ” … a very interesting practical demonstration of the use of the C-tube was given in Boston Harbor. The test was arranged to duplicate as nearly as possible an actual offensive attack upon an enemy submarine: with three (submarine) chasers equipped with C-tubes and various signaling apparatus to intercommunicate the bearings obtained on the submarine. Miniature depth bombs, consisting of electric light bulbs designed to explode 50 feet below the surface, were dropped near the submarine to indicate that it had been located and could actually have been destroyed.

The initial low frequency acoustic sound detector consisted of an inverted T shaped arrangement for surface ships. The sensor at the bonom of the T was a hollow pipe with a 3″ diameter and 5 foot long and fined with rubber spheres at each end. The spacing of the sensors accommodated a frequency of 500 Hz. Frequencies in the acoustic range of 500-1500 Hz were typical. Rubber spheres transmitted the changes in pressure through the vertical pipe to a stethoscope. On surface craft, the tube hung over the side or from the keel. On submarines, it was mounted upright on the deck. The vertical shaft fitted with a wheel could be rotated until the sound was equal in both ears. At this relative bearing, the target was located on a line at right angles to the rubber spheres. This detector was the first use of a binaural method of direction finding. Improved performance was achieved in later models by increasing the number of rubber spheres to 12 and equidistant spacing along the 5 foot section of pipe. Variants of the C-tube concept found application on seaplanes. By June 1918, General Electric Submarine Signal Company delivered 900 C-tubes out of an order of 1000 sets.

C-tube operators achieved ranges of 1000-8000 yards based on 90-second listening and target bearings within 5 degrees.21 According to Friedman, “By June 1927 all U.S. Submarines had 540 Hz oscillators (Fessenden) and SC tubes. “22 The forty-five S-class submarines included C-tube installations from 1917 through the 1930s.

By 1927, all U.S. submarines were equipped with C-tube systems. With new detection equipment introduced in 1934-35, the C-tube that persisted as an instrument of choice on many submarines saw its last removal in 1936.

Some limitations of this new detection equipment were noted. AU .S. Navy officer’s remembrance of hunting submarines aboard a submarine chaser in the English Channel in 1918 concluded that in listening there were 36 good hours for every 100 spent.23 As a rule, in order to listen a United States small combatant was required to be silenced, stop engines and heave to. If the boat rolled, the hydrophone performance was impaired. Submarine chasers stopped every ten minutes. Operation of the detector required the submarine searching ship to be quiet, slow moving, or stationary to detect as the rubber spheres responded to the locally generated noise.

In the Royal Navy’s history of sonar a comment about Nahant’s C-tube is notable. .. … the American listening apparatus was of great benefit to the British war effort both tactically and techni-cally. The C or SC-tube was particularly popular, and more than 500 were in use by the end of the war … the K-tube influenced British hydrophone design during the last years of the war. The binaural compensator, too, was largely an American development.”

K-Tube Drifter Sets

C-tube detectors mounted on the observing platform were hampered by local noise. Further, the limited sensitivity of the rubber spheres led to the development of the K-tube, an off-hull (over the side) drifter detector system using microphones as sensors. In 1917, General Electric and Submarine Signal Company designed an improved small, sensitive, non-resonant, non-direc-tional microphone mounted in a watertight rubber enclosure. is This off-hull drifter detector system could be towed behind the ship or attached to buoys and set to a depth of 40 feet.

The K-tube design consisted of three microphones rigidly mounted at the vertices of an equilateral triangle made of wood. The microphone sensors connected to the receiving platform by cable at distances of 100 feet or more. Aboard ship the output from two of the microphones connected to two telephone receivers and to the operator via flexible air tubes. Detection and bearing determinations were made using a calibrated compensation device.

In some instances, bearings were resolved using the third micro-phone. K-tube systems were widely used during WWI and required the ship to be at rest and all machinery shut down during reception. K-tube torpedo detection with the test ship dead in the water was made at 1000-1500 yards. K-tube detectors located enemy submarines but did not lend themselves to hunting. The detector achieved acoustic ranges of more than 30 miles.

K-tube Under Combat Conditions

In late November 1917, a group of scientists with ties to Nahant sailed to England on USS DELAWARE under the leadership of a U.S. Navy captain to test sample sets of the all of the latest apparatus on British vessels and American destroyers abroad. The equipment to be tested under combat conditions included several K-tubes and the New London Experimental Station’s MF-tubes. 26 As a result of the demonstration of the newly-developed detectors, “The Admiralty was so impressed that by January of 1918 it had organized history’s first sub-hunting expedition.”

Three ten-knot British fishing trawlers were equipped with sound detectors and radiotelephones. On the second day of the New Year on a test in the English Channel aided by an airship U-boat sighting, detection was made from a trawler. An accompany-ing destroyer depth charge panern resulted in a large amount of oil and debris rising to the surface. 28 “As a result of these demonstra-tions, a large number of K-tubes and MF-tubes were requested by the British Admiralty and supplied by this country; and later other forms of detection devices, including tripod listening equipments, were supplied to it.”

K-tube Towed Detectors

Three towed configurations were developed to provide towing at high speed, constant depth, and maintaining its relative base line with the towing vessel or platform. All three configurations used compensation to determination direction. Submarine Signal Company engineered a detector (OV) meeting these requirements. For use with dirigibles, the Nahant engineers devised a system (OK) with the microphones encased in a long rubber tube that could be lowered and towed underwater. During June 1918, towing tests for the (OK) took place by towing from the masthead of the test vessel to simulate dirigible performance.

In April 1918, a towed detector (OS) made with the three microphones mounted on a four foot equilateral triangle and the submarine chaser’s engine shut down could detect a submarine moving at 4 or 5 knots in ranges of 1 to 5 nautical miles. Surface ships detected at 8-15 nautical miles. The direction accuracy was generally better than 10°. In total, 210 detectors were manufactured.

K-tube on Board Detectors

The K-tube mounted on a streamlined frame on the deck or keel of a submarine was called a Y-tube. Deck mountings for sub-merged listening were well forward of the sail or fin and the keel installation for surface operations. Initial tests took place in March 1918, and approval followed the next month. General Electric in Lynn, Massachusetts manufactured 80 complete sets for keel installation and 25 for deck.31 Detectors attached beneath a light-ship were identified as X-tube. Those mounted within a tank inside a ship’s skin were identified as Delta-tube. One hundred were produced for destroyers.

Destroyer System

A destroyer submarine detection system using Fessenden’ s oscillators was developed in the fall of 1917. The oscillators were constructed at the Boston factory of the Submarine Signal Com-pany. The system allowed the observing vessel to follow the movements of a submarine. Four oscillators were located in the forward water tank and shielded from each other by sound screens. The object was detection and pursuit with the destroyer at high speed. With adjacent oscillators connected to a pair of telephone receivers, direction was determined by sound level and compensa-tors provided the angle to the target.

For purposes of conducting tests, Navy permission was obtained to install the detection system on board USS AL YWIN at Submarine Signal’s own expense. On November 14 and 15, intricate testing with a submarine target was successful. With the Fessenden equipment partially dismantled, AL YWIN was ordered to the war zone in Europe. Admiralty tests aboard AL YWIN were successful with the destroyer operating at speeds of up to15 knots. Due to damage to a C-tube installation, AL YWIN was placed in dry dock. At this juncture, presumably the destroyer USS CALD-WELL was outfitted with the Fessenden gear again at Submarine Signal expense. After the Armistice, on board CALDWELL a competitive test was held between the Fessenden equipment and the latest equipment developed by the Submarine Board. The pre-war Fessenden designed equipment prevailed. 32 A comment about Fessenden’s contribution to submarine detection appeared in The History of Engineering During the World War. “The original research and experimental work conducted by Professor Fessenden in connection with the methods and apparatus which he proposed resulted in making available to other investigators knowledge and data the value of which should be fully recognized in the history of submarine detection. ”

In the post-war period, the Nahant SC and Y tube passive detectors were broadly installed aboard U.S. submarines. The Bureau of Engineering focusing on the need for an improved trainable device worked on “supersonics” and “In January 1925 CinC U.S. Fleet drew up a standard sound outfit.”

Research Centers

In November 1918, there were ten main American ASW research centers, including Nahant. Sound, heat, light, and electricity were all given consideration as detection techniques. Most centers were in operation by mid-1917. Seven were supported by The National Academy of Sciences’ arm The National Research Council (NRC) and were located at universities, industrial laboratories, and the Navy Yard in Key West, Florida. One of the largest centers was the Navy Experimental Station located at Fort Trumbull in New London, Connecticut.

Primary U.S. ASW Research Centers During World War I

Sponsorship Location Research
NCB* Nahant, MA hydrophones preliminary sea trials
NRC** Ft. Trumbull New London, CT hydrophones ultrasonics preliminary sea trials
NRC Columbia University New York, NY ultrasonics amplifiers
NRC San Pedro Submarine Committee quarts Rochelle salt magnetostriction
NRC (assistance) General Electric Co. Schenectady, NY Rochelle salt high-freq. oscillators Pliotron (vac. tubes)
NRC Wesleyan University Middletown, CT Rochelle salt
NRC Pasadena, CA Palo Alto, CA (Part of San Pedro Committee) power measuring instruments, cements echo-ranging
NRC Western Electric Co. New York, NY telephonic use of piezoelectricity
USN Navy Yard Key West, FL sea trials
U.S. Goverrunent Bureau of Standards Washington, DC quartz inspection and cutting

* Navy Consulting Board
** National Research Council

With the end of the War, all the research centers were closed. A small wartime group of the personnel at the Fort Trumbull Naval Experimental Station under the leadership of Physicist Harvey C. Hayes moved to the Naval Engineering Station at Annapolis, Maryland. Audio sound problems initiated at New London were continued there as well as further investigation of binaural listening to improve submarine detection by aural meant.


By the end of 1918, 3000 vessels were equipped with detection systems and the human ear was the primary instrument for detection and classification. The United States’ 18-month extensive effort to develop and enhance underwater detection of submarines essentially stopped with the end of hostilities. However, WWI brought a number of transitions in the fighting of wars that continued throughout the rest of the 20th century. One was that government, military, industry, and academic relationships were essential to the development of new technologies to balance the measure versus countenneasure needs of wars. For the first time, WWI saw United States Anny and Navy projects on over 40 campuses. The mix of civilian and military personnel to address the problems related to sound in the sea brought two somewhat different approaches to the search for solutions. Jn some instances the military looked for using available devices for quick answers while the civilian scientists looked for answers from more basic and theoretical research. Later during WWII, some remembered this disparity of viewpoint.

WWI underwater detection efforts in the United States, Great Britain and France provided the basis for a number of detection devices in the years following the War. In the closing days of the War, the United States Scientific Attaches at Rome and Paris witnessed (August 1918}, documented, and commented on an ultrasonic echo-ranging experiment. This was Langevin’s successful sea test near Toulon involving the detection of a submarine with an ultrasonic echo-ranging system using piezo-electric transducers. Jn retrospect, this sea test and the four day four power conference (Italy, U.S., Great Britain, and France) held from October 19-22, 1918 38 discussing underwater echo ranging, ultrasonics, and Langevin’s piezoelectric results provided a starting point for research and developments in the 1920s and beyond.

Beam tilting or steering likewise provided impetus resulting from the wartime effort. Quartz, Rochelle salt, and the magnetostrictive properties of ferrous materials all investigated during the war were available for consideration in transducer use in post war systems. Fessenden’s oscillator, as mentioned previously, found applications until the 1950s. Awareness of science as a tool to fight wars was highlighted by the successful detection devices developed by the team of industrial scientists at Nahant. The United States Navy faced sorting out the various detection devices and making decisions regarding the appropriate detection and other ASW equipment for surface craft and submarines.

In the years immediately following the Armistice, many of the various detecting equipments developed during the war years saw continued and broadened use for the next decade. Devices included the previously discussed SC-tubes, Y-tubes, Fessenden 510 Hz oscillators, and the MV-tube. The MV was one of the better multiple carbon button type microphone receiver listening devices developed at the New London Experimental Station. Proposed by Max Mason 3 July 1917, this set permitted the reception of sound waves from a distant source and essentially eliminated the need of using towed devices. By 1929, detectors with improved performance developed by the Sound Division of the Navy Research Laboratory were replacing the SC-tubes with improved performance.

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