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History of Communications-Electronics in the United States Navy, Captain Linwood S. Howeth, USN (Retired), 1963, pages 261-265:
The Radio Direction Finder
1. EARLY INVESTIGATIONS
The directive properties of propagated radio waves were discovered soon after they became used for communication purposes. Numerous persons, including Sir Oliver Lodge, of England; Andre Blondel, of France; De Forest, Pickard; and Stone, of the United States; and Bellini and Tosi, of Italy, had endeavored to develop equipment utilizing these properties.
2. EARLY U.S. NAVY INTERESTS
Navy interest in the radio direction finder, then called the radiocompass in an effort to stimulate navigational interest, began almost at the time of the initial fleet radio installations. In 1906 the Stone Radio & Telegraph Co., installed a direction-indicating device in the naval collier Lebanon, at their expense, for test purposes.1 The Chief of the Bureau of Equipment addressed a letter to the Secretary of the Navy concerning these tests which stated:
The Bureau has recently been making experiments with a wireless telegraph direction finder on board the collier Lebanon. The results thereon obtained indicate that a development of the system will have a far reaching effect on the safety of vessels at sea, and will possibly play an important part in naval warfare by making it feasible to locate the direction of an enemy's fleet. Indeed the subject is of such importance, in the opinion of the Bureau, that it is deemed advisable, without delay, to thoroughly test out the system on large vessels under sea conditions.2
This equipment did not meet the expectations of the Bureau's personnel due to a multiplicity of reasons. Chief among these was that an antenna, fixed in azimuth, was used. This necessitated the swinging of the ship to obtain the maximum signal and the bearing. The absence of an amplifier to increase the intensity of the signal made it difficult to determine the exact time the ship swung through the point of maximum intensity. Little was known of the radio deviation caused by the closed-looped circuits inherent in ship construction, and these deviations were not compensated for and caused large errors in the bearings obtained.
3. LATER NAVY INTEREST
No further attempt was made to procure direction-finder equipment until 1913. In the fall exercises of that year Hooper endeavored to predict the movements of the opposing exercise force by the simple expedient of comparing signal strengths, and was quite successful in his prediction of the attack hour.3 Following this, he wrote Hepburn of the results obtained during the exercise and recommended that the Bureau investigate the possibility of obtaining direction finders.
By this time both Bellini-Tosi and Telefunken had patented devices for this purpose, and, pursuant to the fleet recommendation, the Bureau purchased one each of these. The Bellini-Tosi apparatus with its large umbrella-type antenna of radial wires about 100 feet in length was installed in the U.S.S. Wyoming for tests. The results were most disappointing. Because of the deviation set up by the many closed loops on the ship and the lack of amplification of the extremely weak signals, all transmissions appeared to be generated from the direction of the ship's heading. To the bitter disappointment of the Fleet Radio Officer, and to the great satisfaction of exponents of the trim-appearing ship, the cumbersome equipment was removed and installed at Cape Cod, Mass., for further tests ashore.4
The Telefunken equipment was not, in the true sense, a direction finder but an early version of the radiobeacon or homer. It consisted of a mast, approximately 100 feet high with antennas radiating from it spaced 200 apart. Each antenna was connected to the transmitter through a rotating device that shorted out all but one in such a manner that the code for a letter assigned to each aerial would be transmitted sequentially on its assigned aerial. The operator of a receiver picking up the signal determined the particular letter which came in the strongest and by reference to a table of letter assignments could determine roughly the reciprocal of the bearing of the transmitter. Obviously, the closer the receiver to the transmitter the smaller the error. This apparatus was usable for rough navigational purposes but was of no military value since it could not provide bearings of enemy transmissions.5 It was installed at Fire Island, N.Y., where it provided bearings with errors of about 5° to 10°.
At the end of 1915 bids were advertised for two shipboard direction finders one each for installation in a battleship and a cruiser. The specifications were very definite and difficult to meet. Proposals were received from the National Electric Signaling Co., the Sperry Instrument Co., and the Marconi Wireless Telegraph Co., of America. The guaranteed bid of the latter firm was accepted and the contract was signed on 28 March 1916. The equipment proved to be an improved Bellini-Tosi equipment. In order to comply with the contract provisions, they were installed in the U.S.S. Pennsylvania and U.S.S. Birmingham, where tests again proved them unsatisfactory. Following this the contract was canceled and the Marconi interests forfeited their bond.6
4. DEVELOPMENT OF A SATISFACTORY METHOD
Dr. Frederick A. Kolster, of the Bureau of Standards, had been earlier employed by the Stone Radio & Telegraph Co., where he became interested in radio direction finding. In 1915 he discovered that a coil of wire wound on a rectangular frame mounted in such a manner that it could be rotated could be used to determine the direction of propagation of radio waves. Using a collector of this type, he found that when the coil was in a plane normal to the incoming waves no current was induced, but when in a plane parallel to them, maximum current was induced. By connecting this loop to a receiver, tuned to the desired frequency, and then rotating it until maximum or minimum signal was received, the direction of the transmitter could be determined by reading the number of degree displacement from the north and south line on a properly installed dial attached to the shaft supporting the coil.7
5. PURCHASE OF RIGHTS UNDER KOLSTER PATENT
Hooper, as Head of the Radio Division, inspected the device and quickly decided that it was exactly what was needed. Kolster was requested to keep it secret, but he advised that he had already discussed it with some of the commercial companies and that one of them had offered him $100,000 in company stock for the instrument. After considerable bargaining he accepted $20,000, retaining the commercial rights upon future release by the Navy. With the agreement of Dr. W. S. Stratton, Chief of the Bureau of Standards, he was employed as a consultant to assist in the adaptation of the apparatus for use aboard ship.8 After World War I the commercial rights were released to him and were sold to the Federal Telegraph Co., for an undisclosed amount.9 The Philadelphia Navy Yard was assigned the responsibility for adapting the Kolster direction finder for ship's installations and for further development.10 Expert Radio Aid E. D. Forbes was placed in charge of the project with Kolster as consultant.
The first equipment constructed was installed there for experimental purposes. Such success was obtained with it that, in November 1926, the Director of Naval Communications requested it remain there as a permanent installation for use in the location of unneutral stations.11 It was decided to locate additional stations along the Atlantic coast for the same purpose and for the detection of enemy signals should we become embroiled in the war. No consideration was given at the time of the establishment of coordinated groups of three around the major Atlantic ports to provide the accurate fixes required to navigate vessels in restricted waters during periods of low visibility.
6. EARLY SHIP INSTALLATIONS
The first adaptation of the Kolster device for ships' installations was for battleships and cruisers. Twenty of these devices were built and installed before the end of 1916. They consisted of a modified version of the Kolster coil, designated SE 74, and a compensating condenser, SE 75, designed by Radio Aid Stuart Ballantine. This condenser, connected between one of the binding posts connecting the coil to the receiver and the ground, made possible the use of the null (minimum signal) method instead of the maximum signal method and increased the accuracy. After installation, the equipment was calibrated to determine the deviation on each target bearing. Prior to the calibration all closed loops had to be bonded to the ship's structure, guns placed in their normal position of train and other movable equipment stored in the usual position. Thereafter, when the direction finder was used, all apparatus had to be returned to the calibration position. In practice, this was uncontrollable, and errors in bearings varied considerably. Compared with present-day equipment it was crude and difficult to use. For example, the reverse bearing could only be eliminated by the inexact and slow process of determining signal intensity.
7. USAGE PROBLEMS WITH EARLY SHIP INSTALLATIONS
The direction finding equipment did not meet with universal acclaim. Many of our senior officers were more devoted to the "hits-per-gun-per-minute dogma," the "big? payoff" for the individual ship commander, than to any innovation which would assist in the detection of the enemy and facilitate in concentrating the greatest possible number of ships at the scene of action in the shortest period of time. To worsen the matter, there was a tendency on the part of all officers to be diffident about things they did not understand. Misnaming this equipment "radiocompass," which it was not, added to their lack of comprehension of its importance, and caused them to label it a "new-fangled device" to replace old and proven methods of navigation. The sole purpose of a radio direction finder installation is to provide the means of determining the bearings of a radio transmitter emitting signals. Whether these bearings be used to determine the position of a distressed ship, an enemy, or an aid in the navigation of ships and aircraft is not a function of the equipment. Bullard, in command of the U.S.S. Arkansas during 1917, wrote Hooper concerning the attitude of the officers. He stated that he found little enthusiasm concerning the compass and that he believed they did not recognize its possibilities and, until they were educated concerning such possibilities, their natural conservatism would militate against its use.12
8. DESTROYER DIRECTION FINDERS
After this country entered the war, our naval officers adapted themselves to innovation more quickly than had been their wont. Allied shipping was being depleted by the German submarine campaign and this method of warfare required ingenuity in the offense.
While the equipment was being installed on the battleships and cruisers, design of sets with smaller coils for destroyers was proceeding. In May 1917, Austin, of the Navy Radio Research Laboratory, advised that the addition of a single vertical wire to the direction finder antenna system would eliminate one of the two nulls, thereby giving positive direction of the transmitting target. This was incorporated in the SE 995 destroyer direction finder. This equipment utilized a 20-inch coil of two windings and the vertical antenna connected to an SE 998 receiver and a SE 1000, two-stage audiofrequency amplifier. This was ready for installation by the summer of 1917 and was greatly superior to the earlier equipment. It was fitted in all destroyers available in continental navy yards and shipped to Brest for installation in those operating from that base.
The young destroyer commanders developed plans utilizing this equipment for locating enemy submarines; effecting concentrations for hunter-killer operations; and for assembling and escorting of convoys in thick weather. They were so successful that by early 1918 the German Submarine Service was completely demoralized and ineffective.
9. THE RADIO DIRECTION FINDER IN THE WAR ZONE
The European belligerents made no endeavor to equip their men-of-war with direction finders, but both England and France established shore systems. England was using its system to track German ships and submarines to great advantage, particularly since the German naval authorities had not been properly indoctrinated in communications security.
Upon our entry into the war, the Navy established an operating base at Brest, France, and most of the logistic supplies from this country entered that port. The Germans concentrated submarines in the Bay of Biscay in an effort to cut this line of supply. Adm. H. B. Wilson, USN, who commanded the U.S. Naval Forces in that area, directed the establishment of three direction-finder stations to cover the Bay of Biscay. These stations were connected with wire communications to the flagship at Brest. German submarine commanders, unaware of the use of direction finders, continued the unrestricted use of radio and allowed themselves to be constantly tracked. Convoys were easily diverted to avoid them. Moreover, in the foggy weather that abounds in the Bay of Biscay the convoys were tracked and directed in or out of port without delay.13
10. IMPROVEMENT OF RADIO DIRECTION-FINDER EQUIPMENT
Late in 1918, the SE 1440 receiver became available. It was especially designed by the Washington Navy Yard for use with direction finders and integrally contained three stages of audiofrequency amplification. It was fitted with a "compass receiver" switch that permitted instant connection to the compass coil or to an ordinary antenna. Together with a 515A coil system and an SE 1762 compensating condenser, it became the model DA shore direction finder. The shipboard installations SE 74 and SE 995 were basically improved by refitting them with the SE 1440 receiver and a newly designed coil, SE 1512. These equipments were much simpler in operation and maintenance and were more accurate.
11. ESTABLISHMENT OF NAVY SHORE DIRECTION-FINDER SYSTEM
Despite the enormous merchant ship program of the United States, the submarine campaign had so depleted Allied shipping that every hour lost by a convoy at sea due to poor visibility or to delay in port was of great seriousness. Additionally, every day they kept at sea because of their inability to enter fogbound ports rendered them that much more vulnerable to the submarine menace.
In early 1918 the Chief of Naval Operations, concerned with the delays of transports by weather conditions, directed his Planning Committee to study the subject and endeavor to eliminate these delays. The Committee recommended the establishment of direction-finder stations in groups of three around the approaches to the harbors of Boston, New York, and Charleston, and the entrances to the Delaware River and the Chesapeake Bay. One station of each group would operate as the master or controlling station and control a transmitter at a distant station by landline. The two "slave" stations would telegraph their bearings to the master, where the plotting would be done and fixes or bearings transmitted to the convoy commander. This was approved, and in June 1918 the sites for these stations were selected.14 Urgent requirements for new ship installations and improvement to existent ones delayed the completion of these shore stations. At the date of the armistice not one of them was in operation. On 26 December the New York group was placed in operation in time to be used by our battleships returning from their duty with the British Fleet. The remaining groups were commissioned rapidly thereafter and hastened the operations of the troopships returning our soldiers from overseas. Their successful operation resulted in the establishment of groups at all important ports in the United States, on the Great Lakes, and at dangerous navigational points along our coasts.
1 S. C. Hooper, "Navy History--Radio, Radar, and Sonar," Recordings, Office of Naval History, Washington, D.C., 31R76.
2 Letter, dated 17 Oct. 1906, from Chief of the Bureau of Equipment to the Secretary of the Navy, files, Bureau of Equipment, National Archives, Washington, D.C.
3 Hooper, op. cit., 17R42.
4 Ibid., 17R43.
5 Ibid., 31R76.
6 Ibid., 31R77.
7 "History of the Bureau of Engineering, Navy Department. During the World War" (Washington, Government Printing Office, 1922), p. 96.
9 Letter, dated 31 Oct. 1922, from the Bureau of Ships to commander in chief, US. Pacific Fleet.
10 These direction finders are described in app. M.
11 "History of the Bureau of Engineering, Navy Department, During the World War," op. cit., p. 97.
12 Hooper, op. cit., recording 32R78.
13 Hooper, op. cit., recording 32R78.
14 Hooper, op. cit., recording 32R79.
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