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History of Communications-Electronics in the United States Navy, Captain Linwood S. Howeth, USN (Retired), 1963, pages 471-478:
It has been stated so often as to become axiomatic that new wars are begun using the equipment developed by the end of the last one. Fortunately for us this was not true insofar as underwater detection and location equipment was concerned. As related in part II, much was done during World War I to develop underwater detection equipment, but that which was put into service was not capable of coping with the submarine problem of that war and would have been entirely useless in combating this menace in World War II. Credit for the continued research following World War I and during the depression of the thirties, when practically all research was discontinued, belongs to the several heads of the Radio and Sound Division of the Bureau of Engineering, to Capt. J. T. Tompkins, USN, Commander Control Force, U.S. Fleet, during a part of that period and to the small group of scientists under the indefatigable leadership of Dr. Harvey C. Hayes, the Navy's senior underwater sound physicist.
It is not the writer's intention to imply that the successful development of satisfactory equipment was in itself sufficient to defeat the German submarine threat of World War II. This would be far from the truth, for improvements in equipments, offensive tactics, studies of oceanography, and concentrated studies of both successes and failures in making kills were necessary. It is, however, only fair that it should be pointed out that sonar was the backbone of all that lead to the checking of submarine operations and winning the victory in the Battle of the Atlantic.
At the beginning of World War II the Germans had approximately 20 500-ton and 10 750-ton submarines. The British had fitted 165 destroyers, 34 small patrol craft and 20 trawlers with asdic, their development of underwater detection equipment. During the first year of the war the number of submarines of the Axis Powers was increased by 60 belonging to Italy. By December 1940 these submarines had sunk 1,201 vessels, an average of 80 per month and Allied shipping had suffered a reduction of 4½ million gross tons. In accomplishing this the Axis lost 47 submarines, an average of 3 per month. During 1941 the German submarines commenced "wolf pack" attacks and extended their operations to the coasts of Greenland and Newfoundland, increased the number of their submarines to approximately 200, and sank 1,118 ships for an average of 93 per month. Asdic-sonar equipped Allied vessels, totalling approximately 800, of which 500 were ocean-going, managed to sink 45 submarines for an average of 4 per month.1
When the United States entered the war, in December 1941, our 170 destroyers were the only United States surface craft fitted with sonar. Seventy-five percent of these were engaged in Atlantic convoying and the remainder were employed in the Pacific. Our Atlantic seaboard shipping was slaughtered at the rate of 75 ships per month by an operating group of approximately 38 submarines, which suffered casualties amounting to only 3 per month. Prior to March 1942, we began convoying our coastal shipping with a woefully inadequate number of vessels and land-based aircraft. Our success in sinking submarines, despite successful detection, was less than 5 percent. We were losing the Battle of the Atlantic.2
In a desperate attempt to find a solution, the Navy Department assigned the National Defense Research Committee of the Office of Scientific Research and Development, a project to provide statistical analysis of past operations, theoretical studies of tactical doctrines, operational analysis of sonar attacks, and of equipment and weapons in order to determine their best methods of use and to improve their design. The committee established the Antisubmarine Warfare Operational Research Group under the direction of Dr. P. M. Morse, with representatives from practically all Offices of the Fleet Headquarters and a group from the British Admiralty which furnished statistics of the Royal Navy's 30 months of war experience. Our ships began to report attack details to this group which quickly developed improved methods of convoying, screening, searching and attack.3
2. THE DEVELOPMENT OF SONAR
Although research in acoustical sound systems was continued after World War I, it was given low priority because of the high losses encountered during the transfer of propeller noises from water to air. High priority was given to the development of an electrical sonic system since little signal strength is lost by transfer from water to microphones connected electrically to telephone headsets. The greatest emphasis was placed on the development of a supersonic (15,000 or more cycles per second) echo-ranging system, because such a system eliminates much of the inherent ocean noises, utilizes a narrower beam, and the received signal is more easily amplified electronically.4
The first experimental sets of this supersonic echo-ranging apparatus were completed prior to 1927 and installed in several naval vessels during that year. They contained a combined transmitting and receiving device called the transducer which consisted of quartz slabs sandwiched between steel discs about 16 inches in diameter. This 4-inch thick assembly protruded through the bottom of the ship. When energized it pinged out pulses of energy of one-quarter second duration, at a frequency between 20,000 and 40,000 cycles per second, which travelled through the water in a sharp cone-shaped beam. Upon striking a solid object a minute portion of the energy was reflected back to the transducer in the same manner as the radiofrequency energy is reflected in radar. From the transducer this reflected energy was transferred through an electronic amplifier and thence to the headset and a range indicator. The bearing of the reflecting object was indicated by the direction the transducer was trained. Only a small amount of energy was transferred to the water and echoes were obtainable up to several hundred feet provided the vessel in which it was installed was slowed to 3 or 4 knots. The development of this equipment was an important forward step but obviously the limitations of speed and distance were a serious handicap.5
At this time the Submarine Signal Co. began producing the Fathometer for sounding. The transmitter of this equipment consisted of an electromagnet which, when energized, caused a piston to hit against a diaphragm, located in the bottom of a hull and exposed to the sea, which emitted a 1,000-cycle-per-second sound wave. The indicator consisted of a motor-driven disc revolving at constant speed behind a fixed dial containing a circular slot through which a neon bulb fixed to the rotating disc was visible. The dial was calibrated in fathoms based on its angular travel and the speed of sound in water. The zero mark was at 12 o'clock and at this position the impact oscillator was energized and the single signal of short duration was transmitted and at the same instant caused the neon bulb to flash. When the echo of this signal was received by a carbon button-type microphone, also electrically connected to the neon bulb, it caused it to flash again. Meanwhile the disc had travelled a specific angular distance, depending upon the depth of the water which was read directly from the calibrated dial at the instant of its flashing. The impact oscillator signal permitted sound measurement of shallow waters. The fathometer became the standard sounding equipment for naval vessels.6
The next important development was by the Hayes group at the Naval Research Laboratory when, in 1929, they produced a listening sonar which replaced the acoustic SC tubes in submarines. This was, in effect, the receiving portion of the echo-ranging sonar and was given the designation JK. Instead of the quartz crystals employed in the echo-ranging apparatus, the JK utilized newly developed rochelle salt crystals which had been found to be more sensitive. The JK transducers were mounted on the top side of all our submarines and increased the listening range to about 5 miles and gave bearings which were accurate within a few degrees. Because of its location this apparatus could be used only when the submarine was submerged. A little later it was modified by the addition of a small transmitter which provided a "ping," similar to that in the echo-ranging apparatus. This was used for underwater communications. A few of the sets were also modified to provide underwater voice communications.7
By 1931 the Laboratory had developed the QB echo-ranging sonar for submarines. It was almost identical to the surface vessel sonar except that it also utilized rochelle salt crystals instead of quartz. This equipment was installed in newly constructed submarines in addition to the JK apparatus. It protruded through the bottom of the hull, thus enabling it to be used when the submarine was surfaced.8
The Washington Navy Yard was the manufacturer of the quartz-steel echo-ranging equipment and had produced about 20 sets by 1933. At that time it also had approximately 60 of the JK devices under construction. In that year the Submarine Signal Co. was given a contract to provide 30 QB equipments.9
At speeds in excess of 5 knots the water noises drowned out target noises and echoes. To reduce the turbulence caused by the movement of the flat-faced transducers, the laboratory, in collaboration with the Goodrich Tire & Rubber Co., produced a spherical cover, of sound transmitting rubber, about 19 inches in diameter. This permitted increasing the speed to about 10 knots before water noises became excessive. Since the speeds of submerged submarines at that time was less than 10 knots, a satisfactory underwater detection system for their use had been developed.10
The invention of a transducer utilizing magnetostriction tubes resulted in the elimination of the quartz and salt crystals commencing in 1934. The magnetostriction tubes are basically small electromagnets inches long and three-eighths of an inch in diameter of hollow nickel alloy tubing, around which is wound a coil of wire. When the magnetic flux is changed the tubes elongate or contact causing a vibration of the attached diaphragm which results in the emission of "pings." Likewise when a sound hits the diaphragm the resultant vibrations cause a change in the magnetic flux of the magnetostriction tubes which in turn causes the generation of an electric current which produces sounds in the phones corresponding to those of the source. The Navy equipment was designed by the Bureau of Ships and the Research Laboratory and was manufactured by the Submarine Signal Co. at an approximate annual rate of 14.11 Following the invention of the magnetostriction transducer, the Submarine Signal Co. adopted it for use in their Fathometers and ceased using the impact oscillator.12
3. OCEANOGRAPHY AND UNDERWATER SOUND
The next several years were devoted to minor improvements of sonar apparatus, developing tactical doctrines and, most important, in the study of the sound-carrying medium, seawater. Shortly after the magnetostriction transducer was incorporated in the sonar equipment, Hayes, the Navy's underwater sound physicist, started a study of the medium. In a cruise from the Chesapeake Bay to Guantanamo Bay, Cuba, the equipment worked perfectly until the ship reached tropical waters. In these waters it picked up strange noises and sometimes failed to receive those which it should. To find the solution to this perplexing situation the Navy contacted the Wood's Hole Oceanographic Institution which dispatched its oceanography vessel, the Atlantis, to Guantanamo. The Atlantis, commanded by Harvard Prof. C. O. Iselin II, and staffed by trained oceanographers, quickly discovered that the difficulty was caused by varying temperatures of different layers of the ocean's waters. This discovery opened an entire new field for the use of underwater sound and necessitated training submariners in the use of oceanography for concealment and for trailing submarines through the ocean's varied conditions.13 To provide this training, the Fleet Sonar School was established at San Diego, Calif., and the Radio and Sound School at the Naval Research Laboratory was also expanded to provide this training.14
4. RESUMPTION OF BRITISH-AMERICAN EXCHANGE OF UNDERWATER SOUND RESEARCH
With the outbreak of World War II, contracts were made with the Submarine Signal Co. and the Radio Corp. of America to produce echo-ranging sonar to equip all of the U.S. Navy destroyers within 6 months.15
When it became evident that we would probably be drawn into the conflict and with our provision of 50 World War I destroyers to the British in payment for leases of bases in their Western Hemisphere territories, there was a resumption of the exchange of scientific knowledge which had been terminated at the close of World War I. It was then discovered that the underwater sound developments in the two countries had been almost parallel. The British had continued the use of quartz-steel transducers in their asdic but had streamlined the dome which housed it. The asdic had the additional advantage over sonar of making a permanent recording of the ranges.16
Since the range recorders provide a valuable aid in conducting attacks the Sangamo Electric Co. was provided information concerning the British device and that company quickly developed an American equivalent. The streamlined dome was adopted permitting speeds to be increased to 15 knots.17
5. INCREASED SCIENTIFIC EFFORT IN DEVELOPMENT AND USE OF UNDERWATER SOUND EQUIPMENT
Despite the excellent detecting capabilities of the equipment the Nazi submariners, well trained in evasive tactics, were being successful in escaping destruction 95 percent of the time.18 Studies of the courses lead to the belief that lack of basic scientific knowledge was handicapping the effective use of sound equipment and that, also, there might be some basic error in design. The National Defense Research Committee formed Division VI, under the leadership of Dr. J. T. Tate in April 1941. A laboratory was established at San Diego, Calif., under the University of California Division of War Research. Research groups were established under Columbia University Division of War Research which included a Theoretical Analysis Group, the Underwater Sound Reference Laboratories, and a Sonar Laboratory at New London, Conn. Sponsorship of the oceanographic work of the Wood's Hole Oceanographic Institution was taken over and the assistance of the Scripps Institution of Oceanography was enlisted. Contracts for services of scientists at numerous universities and colleges were made. All possible unused means of underwater detection were investigated without success and the effort was then concentrated on further development of existing sonar techniques. The Royal Navy contributed its entire experience with antisubmarine warfare and its history of scientific investigations of underwater sound.19
In September 1941, the U.S. Navy began escorting vessels carrying lend-lease equipment. The Nazis retaliated by torpedoing the U.S.S. Kearny and Rueben James. Following these sinkings an undeclared war against Nazi submarines began.20
Upon our formal entry into the war, 170 destroyers were the only vessels the U.S. Navy had fitted with echo-ranging sonar. The Bureau of Ships began equipping torpedo patrol boats, submarine chasers, motorboats, and yachts with lightweight sonar equipments. Production facilities of the Submarine Signal Co. and the Radio Corp. of America were greatly expanded. Other companies such as the Bell Laboratories, the Western Electric Co., and the Bludworth Co., established additional facilities and began supplying sonar's equipments and accessories.21
The Research groups submitted confirmation of the previous supposition that sound is deflected when it passes through regions where a variance of water temperature exists. Bathythermographs were procured and issued both offensive and defensive forces for the purpose of locating thermoclines. The hunter-killer and escort groups used them for the determination of spacing between searching vessels while the submarines used them to assist in evasive tactics.
The Engineering Research Group enlisted the aid of numerous manufacturers and developed three devices which enhanced the utilization of sonar equipment: a "Maintenance of True Bearing" instrument, which keeps the sonar beam on its target during the contacting vessel's maneuvers; an electronic "Bearing Deviation Indicator," which visually indicates when the sonar beam tends to lose contact by being moved away from its target; and a "Reverberation Gain Control," which reduces the heavy reverberations caused by the transmission of pings by the transducer and also reduces undesired echoes from sea growths, shallow water bottoms, tidal. currents, wakes and the noises of marine life.22
The Theoretical Analysis Group developed improved search and tactical doctrines which were immediately placed into use.23
Increased training facilities were established with complete training and coordinating facilities.24
6. SONAR OPERATIONS IN THE ATLANTIC
The effectiveness of the improved Allied antisubmarine measures was demonstrated in November 1942, when 1,065 assorted Allied vessels made passage from United States and United Kingdom ports to wage the north African invasion, with the loss of only 23 ships to a very determined enemy submarine campaign. Elsewhere however, the measures had not yet begun to show results.
Early in 1943 the German submarines were detected utilizing high-frequency radio for the purpose of concentrating for wolf-pack operations. Information regarding operating areas was provided by shore-based direction finders and these areas were searched by shore based aircraft and by hunter-killer groups augmented by escort carriers. When the submarines submerged they were detected by sonobuoys which had been developed for parachuting from planes. Upon contact the echoes activated small transmitters in the sonobuoy which relayed the sounds to the aircraft which would then guide surface vessels to the locale. By summer 1945 planes from escort carriers, provided accurate information as to enemy submarine operating areas and were guiding the hunter-killer groups to these areas. Although the submarines frequently outnumbered the escorts two to one their effectiveness was being reduced. Improved ordnance was also helping to increase the number destroyed.25
In the summer of 1943, Fleet Adm. Ernest J. King, USN, formed the 10th U.S. Fleet with himself as its commander. The nucleus of this fleet was the Antisubmarine Warfare Unit of the Atlantic Fleet. Its assigned tasks consisted of tracking enemy submarines, routing convoys, assigning escorts, and improving uses of weapons and methods of attack. Other activities, with experienced civilian and naval personnel, contributed to the expansion of this fleet. Reports were constantly received by radio and were fed into electronic recording and calculating machines. From the enormous amount of statistical information compiled, improved tactics, doctrines, training, and weapons were evolved. The effectiveness of hunter-killer groups and escorts increased. Towed underwater noise transmitters attracted acoustic homing torpedoes and reduced the number of surface vessels lost. Faster sinking depth charges were developed to reduce the ability of submarines in taking evasive action. Hedgehogs and mousetraps were developed which projected patterns of 30-pound charges, which exploded only by contacting the metal hulls, thereby getting closer to the targets. Additional instruments appended to sonar made it capable of detecting minefields, determining a submarine's depth, providing indication of oncoming torpedoes, of giving more accurate ranges and bearings and to indicate the exact time to fire or launch weapons. Unescorted fast ships were rapidly being fitted with effective hydrophone torpedo detectors which gave them ample time to maneuver, to avoid, and in some instances to attack.26
Admiral Doenitz, the German submarine commander, stated that in the fall of 1943
The boats were ordered to remain on the surface when attacked by aircraft and to cooperate in fighting off the attack. They were then to attack and break up the destroyer screen with acoustic torpedoes, and in the third phase of the battle, attack the convoy now deprived of its protection.
This directive was disastrous to his submarines, for this exposure resulted in a 50-percent loss in effectiveness. In December 1943, he was forced to direct continuous submerged operations. At that time he stated:
It is essential to victory that we make good our scientific disparity and thereby restore to the U-boat its fighting qualities.
At this time German scientists, who had been drafted into military service, were released and aided in the creation of the German Naval Scientific Directional Staff.27
During 1943 the tide reached low-water slack. The Allies lost 598 ships, the Axis 263 submarines. During the winter of 1944 the measures instituted by the 10th Fleet combined with Doenitz's directive for submerged operations resulted in the Allies sinking more submarines than the Axis sank ships. Low-water slack was over and the tide had commenced to flood.28
When the Allies landed in Normandy, the invasion craft were led by scout boats equipped with small echo-ranging equipment equipped with a recorder which traced the outlines of the beaches and located underwater obstacles which were cleared by demolition teams. The invading forces were provided such intense air cover and such tight radar and sonar screens that not a single vessel was lost to submarines for over 3 weeks. The 7 ships lost following that period cost the Germans 21 submarines.29
Just as it appeared that the Allies were winning the Battle of the Atlantic, the Germans developed and equipped their submarines with snorkels which permitted them to recharge their batteries at periscope depth and allowed them to cruise at higher speeds at that depth. Additionally, the exposed portion of the snorkels were covered with a material which reduced the reflection of radar waves. Their new submarines were being constructed with stronger pressure hulls which permitted deeper submergence and offered more resistance to underwater explosions. These actions materially reduced the effectiveness of our air and surface antisubmarine offensive. The Germans took up stalking positions at focal points on convoy routes, lay on the bottom and attacked the convoys with acoustic and looping torpedoes. Radio direction finding ceased to be of assistance since the new strategy eliminated radio transmissions. However, these actions came too late to change the course of events. Their strategy reduced their effectiveness and our improved sonar equipment and operating techniques and countermeasures against homing torpedoes kept the tide flooding.30
The crucial test came during the Battle of the Bulge, during the winter of 1944-45. An operating average of 40 submarines, plus scores of midget submarines, concentrated in the Channel areas in an endeavor to destroy the shipping which was so essential to our hard-pressed land forces. They could not compete with our hunter-killer groups which in the last 4 months of the war sank 88 submarines and approximately 100 midgets while for the same period Allied losses were 56 vessels.31
However, it is generally conceded that continued and constant effort on the part of the Allies would have been required to cope with German improvements. It was Allied opinion that the Germans were constructing submarines which could cruise at submerged speeds which would permit them to outdistance World War II escorts. Only by superiority in science can we hope to keep the peace of the Atlantic.32 "A military research program may be the price of survival."33
7. SONAR OPERATIONS IN THE PACIFIC
Submarine operations in the Pacific were quite the opposite of those in the Atlantic. The Japanese entered the war with 75 seagoing submarines and a few one-man midgets. In the early days they averaged sinking 10 ships per month in the Far East but this rate soon dropped. On the other hand our submarines commenced ranging the Pacific with great success. Japanese escorts were initially equipped with hydrophones incapable of tracking our submarines. In 1943 they commenced equipping them with crude echo-ranging equipment with which they had far less success than we had with the same type at the beginning of the war. Additionally, our submariners were, by this time, well versed in evasive tactics and in the use of bathythermographs to find the thermoclines under which they hid, secure from the Japanese detection equipment. Charts were provided of areas in which intense shrimp noises could be utilized to blanket the sounds generated by the submarine. Our submarine echo-ranging sonar had been augmented with an above-hull 3-foot-long, 2-inch-diameter magnetostriction hydrophone which gave excellent directional accuracy on sounds within 10 miles distance in average water conditions. Listening trainers were provided as a sonar attachment to increase proficiency in estimating target speeds by propeller rhythm. Special mine detecting sonar was provided submarines which made submerged excursions into the Yellow Sea and even into Tokyo Harbor.
By the beginning of 1943, the Japanese Army had overextended its operations in the southwest Pacific and was being cut off from its supplies by a rapidly expanding Pacific Fleet. This necessitated the use of their few remaining submarines for supplying isolated outposts and reconnoitering. Thereafter Japanese submarine attacks were purely those made on targets of opportunity. These were usually thwarted by escorts with fatal results to the Japanese who had gained little experience in evading our improved sonar techniques. During 1943 22 enemy submarines were destroyed in the Pacific. In 1944 they possessed 70 seagoing submarines with operational characteristics comparable with those of other countries but which lacked adequate underwater detection equipment. These submarines were pursued relentlessly by our combined surface and air hunter-killer groups and by our own submarines. How unsafe the Pacific was for enemy submarines is indicated by the fact that three U.S. destroyer escorts, in 11 days at the end of May 1943, utilizing sonar and its ancillaries, sank 6 Japanese submarines.
On the other hand, our submarines were annihilating Japanese shipping with some degree of immunity. So terrific were the Japanese losses on the convoy route between Singapore and Tokyo, that they were wont to say that it was possible to walk between the two ports on the periscopes of American submarines. Actually, only a few of our submarines operated in that particular area at any one time.
During the 6 months of the war in 1945 26 Japanese submarines were sunk, and at the time of the surrender only 43 were left and they were largely being held in port. So ineffective were their operations that we were somewhat lulled into a false security. A few days before the end of the war, the U.S.S. Indianapolis, steaming southward without using evasive tactics, was torpedoed and lost.
The success of our undersea operations and the lack of success of those of the enemy was the measure of our technological advances against their meager improvements. The disparity was so great that oft-times a submarine was destroyed before it appeared to have knowledge that it was opposed.
1 Sonar Press Release, Office of the Chief of Naval Operations, dated 6 April 1946, pp. 5-6.
2 Ibid., pp. 6-8.
3 Ibid., pp. 7-8.
4 Ibid., p. 2.
5 Ibid., pp. 2-3.
6 H. J. Fay, "The Submarine Signal Company" (Soundings, December 1945), p. 8.
7 "Sonar Press Release," op. cit., pp. 2-3.
11 "Sonar," op. cit., p. 3.
13 "Ocean Frontier," Time, vol. LXXIV, no. 1, 6 July 1959; Time Inc., Chicago, Ill., p. 44.
14 "Sonar," op. cit., p. 4.
16 Ibid., pp. 4-5.
17 Ibid., p. 5.
18 Ibid., p. 7.
19 Ibid., p. 6.
21 Ibid., p. 8.
23 Ibid., p. 6.
24 Ibid., p. 7.
25 Ibid., p. 9.
26 Ibid., p. 10.
27 Ibid., p. 4.
30 Ibid., pp. 11-12.
31 Ibid., p. 12.
32 Ibid., p. 14.
33 Statement of Secretary of Defense James E. Forrestal.
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