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History of Communications-Electronics in the United States Navy, Captain Linwood S. Howeth, USN (Retired), 1963, pages 443-469:


CHAPTER  XXXVIII


Radar


1.  PROLOG1

It is doubtful that the development of any electronic system is as confused by as many unsubstantiated claims and conflicting and confusing reports as that of radar. Volumes have been written, some fanciful, some more or less factual, yet colored by pride of discovery or development. Some, written at the instigation of a company or laboratory which had a part in the development, tend to overemphasize particular contributions. In the U.S. Navy the story of its development is further complicated by the divided responsibilities which existed within the Navy Department. The Chief of Naval Operations was charged with providing the military characteristics of equipment. The Chief of the Bureau of Engineering was legally responsible for the development, procurement, and maintenance of electronic equipment. The Chief of the Bureau of Construction and Repair entered the picture to the extent that he was responsible for ship stability. The Chief of the Bureau of Ordnance was responsible for fire-control applications and configurations of equipments for installation in fire control spaces in ships and aircraft. The Chief of the Bureau of Aeronautics was responsible for air search applications and the configuration of installations in aircraft. The Chief of the Bureau of Supplies and Accounts was responsible for contractual procedures. A further complication was the attempt of the joint Communications Board to cope with the chaotic conditions which existed in the electronics industry caused by military requirements far exceeding manufacturing capabilities, by establishing an electronics precedence list which set up a priority system within the priority system which governed all war production. This situation was alleviated to some extent by the consolidation of the Bureau of Engineering and the Bureau of Construction and Repair into the Bureau of Ships on 1 July 1940. Further improvement was brought about by cognizance agreements made between the several bureaus as the war progressed.2
    Radar is a word coined from a contraction of "radio detection and ranging." Its coinage is attributed to two U.S. naval officers, E. F. Furth3 and S. P. Tucker,4 both now retired as rear admirals. On 18 November 1940, the Chief of Naval Operations directed the use of the word as non-classified for reference to the then secret project.5 Prior to 1913 the British called it "radiolocation" and "RDF." The U.S. Army used the term "radio position finding." During that year, by common consent, the term "radar" was adopted by all English-speaking countries.6 It is a method of locating objects by combining the bearings obtained in one or more planes and the range, determined by the time interval between transmission of a radio pulse from the equipment and the receipt of the echo of that pulse by the same equipment after reflection by objects whose positions are desired.

2.  RADAR  PRINCIPLES

In radar systems the transmitter and receiver are normally collocated and utilize a common scanning antenna. The dual use of the antenna is desirable for conservation of space, to assure coalinement of transmitter and receiver antenna patterns, and to simplify the movement of radar beam in azimuth and elevation. Radio energy is transmitted in pulses of about a millionth of a second in duration, the transmitter is then disconnected from the antenna for a few thousandths of a second, then reconnected for transmission of the next pulse, ad infinitum, as long as the set is operated. During the interval the transmitter is disconnected, the receiver is connected to the common antenna, receives the echoes of the preceding pulse from objects in the beam path, and is then disconnected, also ad infinitum. Nearest objects echo signals first and the measure of distance is the elapsed time from pulse to echo multiplied by one-half the speed of light. Bearings of objects are obtained by use of a directional antenna emitting pulses in a sharp beam and upon which the echoed signals impinge. The bearing of the antenna at the time of these dual operations is the relative bearing of the object reflecting the radio waves. For any radar system the beam is narrowed and the gain is increased with an increase in transmitter frequency. For installations where size and weight limitations are controlling factors, higher frequencies are utilized to provide lighter and more compact equipment. Broad beams are generally desirable for search and detection purposes while narrow beams are essential for fire-control purposes. Figure 38-1
    The transmitters of most radar systems use a radiofrequency oscillator containing one or more vacuum tubes which will oscillate at the prescribed frequency and transmit the necessary bursts of instantaneous, relatively high-power radiofrequency energy to the antenna. The modulator takes power from a primary source and provides the suitable voltage pulses to turn on and drive the oscillator violently for an infinitesimal part of a second, turn it off sharply, and keep it quiet during the receiving interval.
    The receiver, although quite small, is an ingenious and complicated piece of equipment. Normally, the superheterodyne principle is used to provide an intermediate frequency which is then highly amplified. The pulse signals require the utilization of receivers of instantaneous response. This necessitates the use of highly specialized, short time-constant circuits. The final stages of the receiver must modulate the signals for suitable presentation to the indicator.
    Radar antennas must be extremely directional, highly efficient, and must leak off none of the power into side lobes since these lobes might produce confusing signals. They must be capable of being directed both vertically and horizontally.
    In many radar systems a low-voltage cathode ray tube is used as the indicator which presents the information in several different forms. This tube became commercially available following its development by the Bell Telephone Laboratories in 1923. In the simplest type of tube the electron beam is given a deflection proportional to time in one direction and to the strength of the echo signal in the other. The position plan indicator tube, with a residual glow screen, measures time from the center of the tube and outward radially in the direction in which the antenna is trained. This type of indicator was developed by Dr. R. N. Page, of the Naval Research Laboratory, during 1941.

3.  EARLY  KNOWLEDGE  OF  RADIO  WAVE  ECHOES

The only difference in radio, heat, and light waves is that of frequency. In 1886, Heinrich Hertz, who discovered the existence of radio waves, demonstrated that these waves were reflected by solid objects. In 1904, patents were granted in several countries on a proposed method of utilizing this property as an obstacle detector and as a navigational aid for ships. Suitable equipment was not developed for these purposes, and the idea remained dormant for almost two decades. In June 1922, Marconi revived it with the suggestion that high frequencies might be used for the radio detection of objects.7

4.  MILITARY  INTEREST  IN  RADIO  DETECTION

Military interest in radio detection was awakened in the fall of 1922 when Dr. A. Hoyt Taylor, who has been given the appellation "Father of Radar," and Mr. Leo Young, both of the Naval Aircraft Radio Laboratory, noted distortion in received signals caused by their reflection from the S.S. Dorchester, a wooden steamer plying the Potomac River. This discovery was reported to the Navy Department with the suggestion that--
destroyers located on a line a number of miles apart could be immediately aware of the passage of an enemy vessel between any two destroyers of the line, irrespective of fog, darkness, or smoke screen.
Figure 38-2 No action was taken on this suggestion at that time.8
    Since a pulse-transmission system had not been developed at the time, there was no possible way of receiving the echoed signals except by use of a receiver located some distance from the transmitter. The presence of moving objects was detectable by the out-of-phase reception of the transmitted groundwave and the reflection of the wave from the object back to the same receiver.
    In June 1930, Mr. L. A. Hyland, an engineer of the Naval Research Laboratory, which had absorbed the Naval Aircraft Laboratory in 1923, was testing a high-frequency direction finder in an airplane on the ground. The Laboratory was emitting radio signals on 32.8 mc. from a horizontally polarized antenna. The plane was equipped with a 15-foot horizontal antenna with the connection to the receiver at about the midpoint. By swinging the plane he was able to obtain a very sharp minimum on the transmissions. While conducting these tests Hyland noted that whenever an airplane appeared in the air nearby, the minimum was disturbed by reflected signals.9 He reported this to Dr. Taylor, who was then Superintendent of the Radio Division of the Laboratory. Further tests confirmed Hyland's report. In November 1930, the Director, Naval Research Laboratory, submitted the Bureau of Engineering a detailed report on "Radio-Echo Signals From Moving Objects."10 Shortly after receipt of this report, the Bureau directed the Laboratory to "investigate the use of radio to detect the presence of enemy vessels and aircraft."11
    Following the Bureau's directive, further experiments with radio wave echoes from aircraft were carried out, utilizing the personnel of the Aircraft Section of the Radio Division of the Laboratory under Mr. C. B. Mirick. This experimentation was expanded to cover frequencies up to about 100 mc. by utilizing portable equipment operated in various locations within 30 miles of Washington. A complete system was devised for the protection of an area of 30 miles in diameter prior to 1932. The protection of this area required the installation of a set of transmitters of moderate power, coupled to directional antennas, operating on frequencies near 100 mc. located around the periphery of a circle enclosing the area. Each transmitter emitted a fan beam directed away from the protected area. Within a few miles these beams gradually overlapped each other. Receivers were located on another circle miles farther out along the beams with their outputs connected by landlines to a central station. Enough of the components of the system were constructed and installed to prove that the presence of aircraft could be detected and their approximate location given when they were within 50 miles of the center of the area to be protected. In the system, detection was afforded by the interferences to the groundwaves traveling directly to the receiver by the radio waves reflected from the aircraft and thence to the receiver, the latter traveling the longer distance, thus establishing an out-of-phase relationship.12
    Since this system was not adaptable to shipboard usage, the Secretary of the Navy, in late 1932, suggested that it might meet the requirements of the Army. That service evinced interest and considered awarding a development contract to the General Electric Co., but before negotiations were completed more effective developments occurred.13
    Pulse transmissions, soon found essential for the successful application of radar principles, were first experimented with for measuring distances in 1925 by Drs. Breit and Tuve, of the Carnegie Institution of Washington, aided by Mr. Leo Young, of the Naval Research Laboratory. These experiments proved successful, and the method soon came into use by other countries for determining ionospheric changes. This resulted in rapid improvements in techniques. Radar really came into existence when it occurred to Young, in March 1934, that pulse transmission might provide a solution to the problems arising from collocating the transmitter and receiver. A year later the same idea occurred to Watson-Webb, who was conducting the British effort in this field.14 Following this, secret work was conducted in many countries involving research in problems of increased power, short pulses, and highly directional antenna systems.15
    Meanwhile, personnel of some industrial laboratories in this country had noted reflection phenomenon. Engineers of the Bell Telephone Laboratories had discussed the subject in an open meeting of the Washington Chapter of the Institute of Radio Engineers on 12 January 1933.16

5.  RADAR  COMPONENT  DEVELOPMENT  NECESSARY  FOR  UTILIZATION  OF  HIGHER  FREQUENCIES

Experimentation with the use of higher frequencies for communication purposes was being conducted at commercial and military laboratories. This involved problems in the development of vacuum tubes which would provide sufficient power at the higher frequencies and a means of transferring high-frequency energy from the transmitter to the antenna. At frequencies up to about 200 mc. conventional, available tubes could be driven to provide adequate power for pulse transmissions. This was sufficient to provide long-range surveillance against aircraft, but the use of higher frequencies was necessary to insure the precision necessary for gunfire control. The losses in normal types of conductors at frequencies above 100 mc. prohibited their use and were a definite hazard in shipboard installations. Figure 38-3
    Several laboratories in this country were of the opinion that they possessed the requisite talent to produce a satisfactory tube for use at the higher frequencies. This was especially true of the Bell Telephone Laboratories. Development projects were established. Despite intense effort, no success had been obtained by October 1940 and no apparent solution was envisaged. Meanwhile, war had commenced in Europe. The British, with their island fortress subject to German bomber attacks, required a longrange surveillance system for protection. The old adage, "Necessity is the mother of invention," proved true in this case. British scientists took an American invention, the cavity magnetron, and improved it to where it was capable of generating enormous surges of radio energy at ultrahigh frequencies.17 This device was invented by Dr. A. W. Hull, of the General Electric Co., in 1921. No practical use was found for it at that time. Scientists of several nations improved it, but failed to appreciate its power potential. In this country Mr. W. F. Curtis, of the Naval Research Laboratory, did important work with magnetrons at about 750 mc. in 1934. Two years later, Messrs. Philpott, Cleeton, and Hagen, of that Laboratory, were using the tube to produce oscillations at 3,000 mc., but did not achieve sufficient reliability to make its operational use feasible.18
    The problem of satisfactory high-frequency conductors was temporarily solved by the radio industry. Their interest in assisting the military in this field was intensified by their desire to utilize higher frequencies for communications and by the advent of television. The Bell Telephone Laboratories developed a semiflexible copper coaxial tubing, and other companies were soon producing similar types of transmission lines of an even more flexible type.19 These coaxial lines solved the immediate problem, but as the frequency and power of radar equipment increased the losses in this type of conductor became too excessive. Waveguides which had been developed by Mr. G. C. Southworth, of the Bell Telephone Laboratories, for communications purposes were then adapted to radar.20

6.  NAVY  RESEARCH  AND  DEVELOPMENT  OF  PULSE  RADAR  SYSTEMS

At the time Young came forward with the suggestion of using pulse transmissions in radar, a special Research Section was organized under him to actively push forward in this and other high-frequency problems. Dr. R. M. Page was immediately placed in charge of the radar project and later was assigned Messrs. L. R. Philpott, R. C. Guthrie, and A. A. Varela as assistants. The selection of Page to head this group was fortunate, for he possesses great ability and has an inventive mind. Taylor credits him with contributing more new ideas in the radar field than any other single individual.21
    Shortly before this, the Director, Naval Research Laboratory, had advised the Chief of the Bureau of Ordnance by letter about the possibilities of controlling gunfire by microwave radio.22 This letter was referred to the Special Board of Ordnance for study. One of the conclusions of this board set forth in a memorandum, dated 20 March 1934, stated that--
--if the development of the application of radio microwaves was to be accelerated, which in view of its military importance appears to be highly desirable incentive must be supplied or the work must be done by the Army and Navy.
    During 1934, Page designed and constructed the first pulse radar transmitter operating at 60 mc.23 During tests conducted in December with improvised receiving apparatus, saturation signals were received from a small airplane at 1 mile. The following year was spent solving the problems peculiar to reception of microsecond pulses with an extremely high gain receiver in the immediate proximity of a transmitter radiating many kilowatts in pulses on the same frequency. New equipment was constructed to operate of 28.6 mc. to utilize an existing large beam antenna built to that frequency. At the suggestion of Philpott a self-keying transmitter was utilized. This transmitter and auxiliary components were built by Guthrie, who assisted Page in the system assembly and trials.24
    Trials of this newly constructed radar equipment were commenced in late April 1936 and were continued throughout May with great success. Aircraft were detected and located at ranges up to 25 miles, the limit of the range scale used. The equipment was shown and its operation demonstrated to high Navy Department officials on 10 June 1936.25 A team of electronic engineers of the Navy, consisting of Page, Philpott, and Guthrie under the direction of Young, demonstrated a more sophisticated system, the success of which was nothing short of spectacular. However, additional development was necessary before it could be adapted to shipboard installation. On 2 June, Rear Adm. H. G. Bowen, USN, Chief of the Bureau of Engineering, classified the project as secret and directed that it be given the highest possible priority.26
    Shipboard installation necessitated the use of a much smaller antenna. This was accomplished by two major developments; 200-mc. radar and common use of one antenna for both transmitting and receiving. In 1 month Varela developed this transmitter and made it suitable for trials. Following a suggestion by Young, Page developed a duplexer for common antenna use at 200 mc. This ingenious device, which connects the transmitter and disconnects the receiver and vice versa for the infinitesimal periods of time necessary to prevent paralyzation of the receiver during transmission and yet allow it to be connected for the reception of the reflected radio waves, was successfully incorporated in the equipment. It later became common to all radar equipments.27 In 1954, Young and Page were granted a U.S. patent on this component. Figure 38-4
    By August 1936, 200-mc. radar with one antenna for transmitting and receiving was a reality in the laboratory. It required 18 months to raise this embryonic equipment to the stature of power, sensitivity, and reliability that justified design for service use, and another year to perfect it into a piece of finished service equipment.
    On 18 January 1937, the Naval Research Laboratory was directed to demonstrate and make complete disclosures of its radar development to representatives from the U.S. Army Signal Corps Laboratory, Fort Monmouth, N.J.28 At that time the Signal Corps Laboratory had not succeeded in developing a satisfactory pulse transmission system. Later, on 30 July 1937, the Signal Corps demonstrated a pulse-type radar based upon development work accomplished after the demonstration of the Navy equipment.
    In April 1937, the Honorable Charles Edison, Assistant Secretary of the Navy, and Adm. William D. Leahy, USN, Chief of Naval Operations, witnessed a demonstration of radar equipment at the Naval Research Laboratory, became convinced of its capabilities, and thereafter ardently supported the project.29 The U.S.S. Leary, an old four-stack destroyer, was concurrently made available for testing the equipment at sea. The 200-mc. radar set constructed the previous year was temporarily installed with the antenna affixed to a 5-inch gun mount in order that it might be trained in azimuth and elevation.30
    This radar located planes at ranges of 18 miles during the seaborne tests. Ranges were limited because of the small amount of power which could be generated by available triodes at the frequency necessitated by the size of the antenna. Taylor later stated that he was much encouraged at this time because it was shown that radar would work under seagoing conditions, without seriously interfering with other equipment, and that he was aware of numerous improvements which could be made to greatly increase its range and reliability.31
    On 13 July 1937, at the direction of the Chief of the Bureau of Engineering, complete disclosure of all technical details of radar development were made to engineers of the Bell Telephone Laboratories in the hope that their affiliate, the Western Electric Co., might accept a contract for the development of an engineered equipment for shipboard test.32 These engineers stated that the Naval Research Laboratory had "very beautifully" laid research foundations and demonstrated ultimate feasibility, but that an enormous amount of practical development was necessary. They agreed upon the importance of having special tubes designed for the work, and considered that their Laboratory "had the talent to design such tubes."33 After this conference, the Western Electric Co. officials decided to withhold bidding on an engineered model of the Research Laboratory equipment and, in lieu thereof, to make a proposal for the development of a 700-mc. equipment.34
    Meanwhile, the Laboratory continued its development of 200-mc. radar. The most pressing need was an oscillator capable of generating the required power at that frequency. In November 1937, Page suggested the use of a "multiple-tube, ring-mounted transmitting oscillator."35 This suggestion was developed by him with the assistance of Guthrie and Varela and resulted in the construction of a series of multiple-tube oscillators at very high frequency, in which efficiency was not degraded by adding up to 12 tubes in each oscillator. The 100TH tube developed by Eitel-McCullough, Inc., for use in amateur radio transmitters was selected for use in the multiple-tube oscillator. At their rated plate voltage of 3-kv. they could scarcely be made to oscillate at a frequency of 200 mc., but in a six-tube ring, pulsed at 15 kv., they generated over 1 kw. per tube pulse power.36 This new oscillator was incorporated in a "breadboard" model of 200 mc. equipment, and placed under test at the Laboratory early in 1938 where it was successful in detecting planes up to ranges of 100 miles.37

7.  NAVY  SERVICE  TESTS  OF  SHIPBORNE  RADAR

A conference, attended by representatives of the Chief of Naval Operations, the Naval Research Laboratory, and interested bureaus, was held on 24 February 1938. At this time representatives of the Chief of Naval Operations demanded that a model of the Laboratory equipment be placed in the fleet for detection purposes. The Chief of the Bureau of Ordnance concurred, but asked that the development of radar for fire-control purposes be continued.38 The Laboratory was to complete the construction of a 200-mc. radar for installation in a ship, prior to the end of the year, for service tests. The U.S.S. New York was selected for the experimental installation of this equipment, which was given the designation "XAF." The top of the conning tower, located just forward of the foremast, was selected for the antenna installation which, because of its size, about 17 feet square, and appearance, was dubbed the "flying mattress." Installation was completed during December 1938. During March 1938 the Bureau of Engineering disclosed the basic principles of radar to designated engineers of the Radio Corp. of America and contracted with that company for the development of an experimental set in the 400-mc. band. The contract required that this be ready for installation and test by the end of 1938. This was a difficult requirement because of the limited experience of these engineers in the radar field. Nevertheless, the equipment, designated CXZ, although not satisfactorily developed, was installed in the U.S.S. Texas during December 1938.39 It is of interest to note that the cost of the XAF was less than $17,000 as compared with the $60,000 paid for the CXZ.40 Figure 38-5
    The huge rotating antenna for the XAF, which had to be built as light as possible consistent with strength necessary to withstand high wind pressures, was constructed by the Brewster Aeronautical Corp. This company was experienced in duralumin construction.41
    Both equipments were given exhaustive tests during winter maneuvers and battle practices in the Caribbean. As a result of the too-short period allowed the Radio Corp. engineers to develop the CXZ, the XAF was better engineered. The higher frequency of the CXZ permitted use of a much smaller antenna.
    The Naval Research Laboratory equipment proved ever more satisfactory and reliable than was expected. It operated for nearly 3 months on an average of almost 20 hours a day. There were only two breakdowns in the entire period, both of which were due to tube failures and were corrected immediately by replacement of the faulty tubes. It was used for navigational purposes, for surface and air detection, for spotting the fall of shot, and, to the surprise of all, for tracking projectiles in flight.42
    Unfortunately, the hastily designed and constructed CXZ was unable to produce good results, but the Radio Corp. engineers learned enough to insure that their next model would be more practical.43
    The unsatisfactory state of development of the CXZ radar resulted in the Chief of the Bureau of Engineering recommending to the Chief of Naval Operations that a full exchange of technical information be permitted between the radar groups of the Naval Research Laboratory and the Radio Corp. of America. He considered this a necessary educational program for the commercial companies which would have to do much of the final development and engineering prior to quantity production.44
    Upon the completion of tests Capt. R. M. Griffin, USN, commanding the U.S.S. New York, recommended the XAF be installed immediately on all Navy aircraft carriers. Rear Adm. A. W. Johnson, USN, Commander, Atlantic Squadron, in forwarding the New York report, stated, "The XAF equipment is one of the most important military developments since the advent of radio itself. The development of the equipment is such as to make it now a permanent installation in cruisers and carriers."45 The Commanding Officer, U.S.S. Texas, considered the CXZ, as installed, of little value, but recommended that the Navy Department continue to encourage and assist the Radio Corp. in its development.46

8.  INITIAL  NAVY  PROCUREMENT  OF  COMMERCIALLY  ENGINEERED  RADARS

On 1 May 1939, the Chief of Naval Operations held a policy conference to reach decisions concerning manufacture and installations of radar equipments. Based upon Page's report and the glowing reports from the Fleet, officers of the Office of the Chief of Naval Operations desired that 20 exact copies of the XAF be procured. The Bureau of Engineering demurred on the ground that further improvement was desirable. A compromise agreement was reached that 10 equipments would be placed under contract.47
    On 18 May 1939, the details of the XAF radar were disclosed to engineers of the Western Electric Co. Laboratories and on the following day to engineers of the Radio Corp. of America. Prior to June, complete specifications for "radio range equipment" were ready for the prospective bids of the two companies. However, in lieu of contracting for 20 sets as recommended by Operations, the Bureau decided to purchase only 6 sets on the first contract and to later contract for others of an improved version based on knowledge gained under the initial contract.48
    The contract was awarded the Radio Corp. of America in October 1939, with the understanding that the Naval Research Laboratory would assist in every possible manner. The XAF was delivered to the contractor the following month and the first production models, designated CXAM, were delivered in May 1940. These equipments were fitted in the U.S.S. California, Yorktown, Chicago, Pensacola, and Northampton.49
    The Research Laboratory had succeeded in developing a detection system which would, in the near future, revolutionize naval warfare. Despite this, there was difficulty in procuring sufficient funds to press the project with the necessary rapidity. This stemmed from the natural conservatism of our naval officers and from an economy imposed upon them during the depression of the thirties. Incredible as it may seem, the Bureau of Engineering, in 1939, requested and obtained only $25,000, exclusive of the salaries of its engineers, for electronics research.50

9.  INCREASED  RADAR  DEVELOPMENT  BY  THE  NAVY

Late in 1939, Page submitted a report to Rear Adm. H. G. Bowen, USN, who, upon finishing his term as Chief of the Bureau of Engineering, had become Director, Naval Research Laboratory. This report emphasized that antenna size could be greatly reduced by the utilization of higher frequencies, but that this necessitated awaiting the development of a new type of tube. The report stated that the 500-mc. equipment then under development functioned well up to 20,000 feet; that development was continuing along two lines, one for longer-range detection at about 200 mc. and the second for the use of higher frequencies for altimeter, fire-control, and bombing equipments; and that it was hoped that the Navy would shortly be in a position to use radar on bombing planes. This report was forwarded the Secretary of the Navy on 8 December.51
    Another Laboratory report, addressed to the Bureau of Engineering, dated 26 February 1940, again emphasized the developments of equipments using higher frequencies and stated the importance of integrating recognition equipment with radar. It further emphasized the necessity of integrating radar in the fire-control system and the development of repeater units and the plan position indicator.52
    On 30 April 1940, seven important phases of radar which should be developed were listed. Because of lack of personnel and facilities, work was proceeding on only basic development, detection of surface vessels and aircraft from both surface and airborne craft, and aircraft detection from submarines. In a letter dated 7 May 1940, the Bureau stated that--
the inherent possibilities of radar offer compelling reasons for the development of all its phases insofar as consistent with reasonable economy.
Figure 38-6 In replying to this the Laboratory requested that it be allocated over twice as much money for radar development during the coming fiscal year as had been granted them for the one which was drawing to a close. On 28 May 1940, the Chief of the Bureau of Engineering cautioned against proceeding too rapidly with the program, stating that, unless care were exercised, with rapid changes in this new field, unlimited funds could be expended and that reasonable economy dictated the awaiting of developments.53
    On 1 June 1940, the Chief of Naval Operations directed a letter to the Chief of the Bureau of Engineering which stated in part:
In view of the present international situation it is desired that every effort be made to expedite the completion of the development of the project in all its phases and to commence procurement at the earliest possible date that is justified by the success obtained in every subdivision of the project. Accordingly it is suggested that expansion of facilities and personnel be undertaken as soon as funds are in hand.54
    On 1 July 1940, the Bureau of Engineering and the Bureau of Construction and Repair were consolidated in the newly created Bureau of Ships. The urgings of the Chief of Naval Operations were heeded by the Chief of the new Bureau, Rear Adm. (later vice admiral) S. M. Robinson, USN. A contract for 14 CXAM-1 radar equipments was negotiated with the Radio Corp. of America. The specifications for this new version called for an improved antenna and for amplidyne instead of thyratron, control.55 On 23 July 1940, the Western Electric Co. was awarded the contract for surface fire-control radar equipment operating on 500 mc. At this time a memorandum by the Chief of the new Bureau stated that the radar program initiated by the Chief of Naval Operations would require $10 million in 1941 and $20 million in 1942. Immediate steps were taken to increase the personnel and to provide facilities necessary to insure that the equipment purchased with these funds would meet naval requirements.56
    It was becoming apparent to many that there was a strong likelihood of our being drawn into the war. With this feeling, there began in the United States an era of enormous scientific development. Inventive imagination exceeded design and development which, in turn, far outstripped engineering and manufacturing capabilities. The problems requiring solution greatly exceeded the personnel and laboratory facilities provided by our Government, commercial, private, and educational institutions.
    The electronic engineers of the Naval Research Laboratory were doing all they could with what they had. To them, and to those who provided them with encouragement, must go the credit for the superior electronics installations which existed on our combatant vessels during World War II. It was mostly with the equipment designed and developed during this period that the war at sea was fought. In addition to the development of the search radar and the guidance afforded the Bell Telephone Laboratories in their development of fire-control radars, there were other important requirements met by their scientific knowledge and long and arduous hours of labor. Many of these were in other fields of electronics and are covered in other chapters.
    Following the development of the CXAM radar, work was immediately commenced to design similar equipment for smaller vessels. This was a 200-mc. search radar of higher power using a much smaller antenna. The Laboratory's model was designated XAR. The contract for engineering and producing this equipment was awarded the General Electric Co. The preproduction models of this equipment were delivered before they were able to equal the performance of the pilot model provided by the Laboratory. These were purchased in large quantities and bore the designation SC. Similar equipment produced a little later by the Radio Corp. of America carried the designation SA. Although these equipments were rendered obsolete by later microwave developments they were used extensively in all theaters.57 Figure 38-7
    Another development, which has been previously mentioned, was the plan position indicator. This oscilloscope greatly simplified the radar presentation of the target, by placing the radar transmitter in the center of the screen and target presentation on lines of bearing, either relative or true against range scales emanating from the center of the screen. Development was completed and the indicator placed in production just prior to our entry in the war. It was welcomed by Americans and British alike. After the war, Page was granted a U.S. patent on this invention.58
    With the increased operational ability of aircraft, there became a serious threat to submarines, and it was realized that some method of aircraft warning was essential. The use of radar for this purpose was difficult because a large directive antenna would offer too much water resistance to a submerged submarine and would be difficult to house. The Research Laboratory was directed to proceed with the development of a warning radar, using a periscope antenna. Target bearing was not made a requirement since the submarine defense against aircraft is in crashdiving. Mr. R. C. Guthrie was assigned the project in March 1940. It was decided to use the 114-mc. band. Later it was taken over and completed by Mr. A. A. Varela. The first production units of the equipment, designated SD, were constructed by the Radio Corp. of America. During the latter years of the war, the Japanese developed an aircraft receiver covering this frequency band and used the radar transmissions for homing, resulting in the loss of a few of our submarines. As with the SA and SC, development of microwave radar equipment rendered the SD obsolete, and these equipments were replaced by others which could not be utilized offensively by the enemy.59
    One of the earliest requirements for aircraft safety was an altimeter which would indicate relative rather than absolute altitude. At the time pulse transmission was adapted to radar, it was realized that a radio pulse altimeter might become a possibility. With the development of the Young-Page duplexing system it became a reality. Its development, using a 500-mc. transmitter, was completed by the Laboratory and it was placed into production.
    In the fall of 1940 the British supplied the Laboratory complete information on their 175 mc. airborne search radar. The Bureau of Ships purchased a quantity of these ASV equipments for installation in patrol planes. The ASV, because of its low frequency and because the British had not developed a duplexing system, required a number of large antennas. These sets were modified by adding a duplexing system. The Laboratory considered that an airborne search radar would be more efficient, smaller, and lighter if a higher frequency could be utilized. In January 1941, they commenced converting the radio pulse altimeter into an airborne search radar. By October 1941, sufficient information had been provided the Westinghouse Electric & Manufacturing Co. for them to start preproduction models. A month later the Radio Corp. was provided all information on this development and they started work on preproduction models. This American airborne search radar, designated ASB, went into full production in the spring of 1942 with the first equipments being delivered in May. Over 26,000 were produced for American and British military services. Although it, too, became obsolete by the later development of a microwave airborne search radar, many were still being used at the war's end.60
    During the early months of the war, positive identification of distant aircraft was most difficult. Friendly planes were required to approach naval vessels within a specified variable sector. Even when within the correct sector, they were subject to challenge by searchlight, following which they had to immediately halt progress toward the challenging ship and identify themselves by a periodically varying maneuver and remain away until the challenge was removed. That this was a most unsatisfactory procedure had been earlier recognized. The Naval Research Laboratory personnel had this problem under consideration for several years and were successful in developing several systems integrated with radar, one of which became the basis of the Mark V system adopted by the Allies.61

10.  PREWAR  RESEARCH  AND  DEVELOPMENT  OF  RADAR  BY  THE  ARMY  SIGNAL  CORPS

The Army had conducted intermittent research on aircraft detection and location systems since the end of World War I. In 1930 the responsibility for research in this field was transferred from the Ordnance Department to the Signal Corps. The project was assigned the Signal Corps Laboratory at Fort Monmouth, N.J., which at the time was under the command of Col. William R. Blair, Signal Corps, USA. Research was instituted in both infrared and radio methods. For the latter the use of microwaves a few centimeters in length was directed. Experiments with these resulted in the obtainment of echoes from nearby objects, but the ranges were not sufficient to make equipment practical for operational use. This prompted Blair to state, in his annual report for fiscal year that "a new approach to the problem is essential."62 Figure 38-8
    When it was suggested by the Secretary of the Navy, in 1932, that the detection system developed by the Naval Research Laboratory might be of more value to the Army than to the Navy, the Laboratory informed the Signal Corps of the development and from that time on there was a complete exchange of information on radar projects by both services.63 The Signal Corps began negotiations with the General Electric Co. to develop this system. These negotiations were terminated because both the Naval Research Laboratory and the Signal Corps Laboratory began the development of pulse radar systems which appeared to offer greater promise.
    The 4 June 1936 demonstration of the Navy's 28-mc. pulse-type equipment was witnessed by Blair and his assistants. They were provided full information concerning the newly developed equipment and were shown the work accomplished on the 200-mc. equipment which was later tested in the U.S.S. Leary. During conversations held at that time, Taylor advised Blair to continue work in the 100-mc. band since Army usage was not too severely limited by antenna size. With the lower frequency a much higher peak pulse power could be obtained with available transmitting tubes.64
    The War Department, on 29 February 1936, directed the Chief Signal Officer to give the highest priority to the development of a detector system for antiaircraft battery use. This directive had been anticipated, and early in 1936 the Signal Corps Laboratory designed a complete radar system. The technique utilized failed to give the necessary instantaneous peak pulse power, but by the end of 1936 some echoes from pulses directed at commercial planes flying on a regular airway in New Jersey had been detected. On 18 January 1937, representatives of the Signal Corps Laboratory were shown the pulsing technique developed by the Naval Research Laboratory. Based upon this information they redesigned their equipment. On 30 July 1937, the pilot model of this redesigned system, later designated SCR 268, was successfully demonstrated against a flight of test bombers in the presence of the Secretary of War and several Members of Congress. It transmitted train and elevation information to a director which enabled searchlights to be pointed and trained so that they could be turned on a plane instantly when it came within range.65
    Following this the equipment was mounted on mobile antiaircraft artillery director trucks, where it replaced the sound locators previously used during periods of low visibility. In November 1938, this was demonstrated to the Army Coast Artillery Board which shortly thereafter requested the Chief Signal Officer to produce "a radio detection device which will provide accurate azimuth, accurate angular height, and accurate slant range for use as basic firing data for antiaircraft guns."66
    Acting upon this request, the SCR 268 was improved in accuracy and modified to feed its output to an automatic calculator, the output of which, in turn, was fed to the gun directors. While this equipment was not extremely accurate, it was used in all theaters of operation during World War II and was the backbone of the early warning system installed along our coasts and in our insular possessions.67
    The Signal Corps made no contribution to the development of airborne radar. The British ASV, the U.S. Navy's ASB, and the Radiation Laboratory's microwave ASV were utilized successively by the U.S. Army Air Force.68

11.  PREWAR  DEVELOPMENT  OF  FIRE-CONTROL  RADAR

Following the decision of Western Electric Co. officials to develop radar equipment using frequencies in the spectrum between 500 and 700 mc., its parent corporation, the American Telephone & Telegraph Co., agreed to underwrite a research project for the preliminary investigation of radio object locations systems in an amount not to exceed $50,000. Assured of financial support, the Bell Telephone Laboratories, corporate associate of Western Electric, prepared a "Preliminary Development Estimate for U.S. Navy Project No. 2," covering the work proposed to be carried out between 1 April 1938 and 15 December 1939. This consisted of the following problems: (1) The determination of minimum sizes and types of projectors required to obtain the requisite directivity utilizing frequencies in the 300-700 mc. band; (2) the determination of the required instantaneous power in the transmitted pulse to obtain desired ranges from transmitters operating in the 300-700 mc. band; and (3) the determination of the required duration of the transmitted pulse and the degree of precision necessary in measuring the elapsed time between transmission and reception. During October 1937, Dr. F. B. Jewett, Director of the Laboratories, discussed this developmental program with naval officials, and an informal agreement was reached. The American Telephone & Telegraph Co. subsidiaries started work on their project to determine for themselves the requirements, capabilities, and limitations of this new technique. At this time selected engineers from their laboratories were given complete information on the Naval Research Laboratory's work and were thereafter kept advised of Navy progress in the field.69
    The Bell Telephone Laboratories established a field laboratory near Whippany, N.J., and on 1 May 1938 assigned Messrs. W. C. Tinus, W. M. Kellogg, and A. G. Fox to make the required determinations. Other divisions of the Laboratories were assigned projects to develop satisfactory components. By May 1939, an equipment operating at 500 mc. had been designed, assembled, and tested. These tests indicated that the precision obtainable with existing techniques was sufficient to make the device useful for certain military and commercial applications but not for the control of gunfire. The $50,000 made available in 1937 was expended by July 1939. The American Telephone & Telegraph Co. authorized the expenditure of an additional $20,000 for continued investigation and improvement of the system. Following improvement which resulted from this, the Western Electric Co., on 15 August 1939, submitted the Bureau of Engineering a proposal with descriptive specifications for the construction of a fire-control radar operating at 500 mc. In April 1940, the Western Electric Co. was issued a development contract for one fire-control radar, designated CXAS, with a delivery date of 15 October of the same year.70
    A series of exchanges of information between engineers of the Naval Research Laboratory and Bell Laboratories during the first months of 1940 resulted in improvement in techniques and components and necessitated a revision of the specifications. The revisions were submitted and accepted by the Navy on 19 August 1940. Incorporating the improvements resulted in an acceptable delay in delivery of about 2 months.71
    The development model of the CXAS was tested during December at Atlantic Highlands, the scene of earlier naval radio experimentation. On 30 December, the equipment was delivered to the Navy. The oscillator, consisting of two triodes in push-pull, produced instantaneous peak pulse power of 2 kw. The Young-Page duplexer was utilized.72
    When, on 2 December 1940, it appeared that the CXAS equipment would meet the specification, an additional contract was issued the Western Electric Co. for 10 model CXAS-1 equipments. They were purchased for installation in the main battery fire-control systems of one heavy and nine light cruisers. This designation of the CXAS-1 was subsequently changed to Model FA.73
    Production of Model FA radars commenced in June 1941. Serial No. 1 was delivered at the end of that month and installed during the following month in the U.S.S. Wichita. An excerpt from this ship's report on the first 525 hours of operation of this equipment is quoted:
Though the Model FA equipment is intended primarily as an ordnance range finder its greatest value at present lies in its ability to detect and the security furnished thereby. With this in mind it was decided to operate the radar continuously while cruising outside United States territorial waters. Continuous operation was maintained successfully for about thirty-six hours, the only interruptions being those necessary for frequent oscillator tube renewals. During this period the sea was calm and several targets were located. It is interesting to note that two expected transports (high free board) were located at 55,000 yards and became distinguishable as two vessels at 44,000 yards. Several detections were made between 20,000 and 30,000 yards but poor visibility prevented identification of targets. In general the operators were seamen with some training but little operational experience, nevertheless the results obtained were satisfactory and demonstrated the practicability of shipboard use.74
Figure 38-9     The FA radar performed satisfactorily when operating at peak performance, but this performance was difficult to maintain because of the relatively short life (about 75 hours) of the oscillator tubes. The operator was required to swing the antenna back and forth manually while watching the oscilloscope, during which time he estimated the range. Continuous target tracking could be accomplished if a more sensitive means of detecting target movement with respect to beam axis could be developed,75 and this was eventually achieved.
    The Bureau of Ships radar personnel conferred with those of the Bureau of Ordnance and Bell Telephone Laboratories on 14 February 1941. The purpose of this meeting was to determine whether a further modification of the Model FA radar could be accomplished to satisfy the requirements of the Bureau of Ordnance for a continuous tracking radar for each main battery and each antiaircraft gun director. The Bureau of Ordnance representatives suggested separating the console of the Model FA and locating the controls of the equipment and the indicator in the gun director. The Bell Telephone Laboratories representatives accomplished this prior to June 1941. By this time the Bell Telephone Laboratories had incorporated "lobing," a means of remotely and rapidly moving the beam of a highly directive antenna back and forth from its normal axis. A method of incorporating this, along with other essential controls and an indicator for the range operator and another for the azimuth trainer, was evolved. An anticipated requirement for rapidly shifting back and forth between radar and optical controls indicated the desirability that each control operator should handle data from both sources. The radar antenna and the optical rangefinder were interconnected so that both were always trained on the same bearing. This permitted the use of the existing data transmission system and eliminated any break in data transmission when shifting from one method of control to the other. While this desirable development was underway it became obvious that the long-searched-for tube which would provide satisfactory instantaneous peak pulse power might become available.76
    Following the arrival of the British technical mission in this country in September 1940, mutual disclosures of great value to both countries were made of developments in the radar field. The United States was advised of the British improvement to the cavity magnetron which made it capable of supplying oscillator power in the microwave band. In exchange, British scientists received much needed information concerning the details of the Young-Page duplexing system.77
    On 3 October, a magnetron of British manufacture was delivered to the Bell Telephone Laboratories. This tube was successfully operated in hastily assembled equipment and in great secrecy on Sunday, 6 October. It produced not less than 6.4-kw. peak power pulses at a frequency of 3000 mc. The best velocity variation tubes existing in this country at that time produced peak power pulse of about 75 watts at that frequency. This tube did, however, generate several additional confusing frequencies. In order to gain further knowledge of its operation and to evaluate its variable elements additional tubes were required. The first multicavity resonator magnetron constructed in this country was completed on 10 October at the Bell Telephone Laboratories electronics laboratory using an X-ray photograph of the British tube in conjunction with some supplementary information provided by the British scientists. On 15 November, five facsimiles were delivered to the Radiation Laboratory, Cambridge, Mass., which had been recently established by the National Defense Research Council for the purpose of conducting microwave research.78
    Intensified research was conducted at the Bell Telephone Laboratories and the Radiation Laboratory. Attempts were made to apply the same principles to the design of tubes generating both higher and lower frequencies and of higher power and efficiency at all frequencies. Concurrently, Dr. M. J. Kelly, Bell Telephone Laboratories, instituted the development of a 700-mc. magnetron for use in fire-control radars. This tube was completed on 23 December. Just prior to its being tested it was accidentally dropped by the engineer who had been working around the clock to complete it.
    It was broken beyond repair. A second 700-mc. tube was completed on 14 February 1941 and tested. It produced peak power pulses of 30 kw. Following this, additional improvements were incorporated. A satisfactorily redesigned tube was completed in May and placed in production. The production models produced an output of 40 kw. with an efficiency of approximately 40 percent.79
    Concurrently with the development of an American 700-mc. magnetron, other Bell engineers were working upon one for utilization at 10,000 mc. This was completed on 18 January 1941. It produced only 9-kw. peak pulse power at less than 10-percent efficiency. In an endeavor to save weight and reduce power requirements they commenced the development of a permanent magnet to replace the electromagnet used in their first 10,000-mc. tube. It was completed and tested on 11 June, at which time it furnished an output of 15 kw. at 20-percent efficiency. Plans were made to place this tube in production but before this could be accomplished the British came forward with still another development.80
    In November 1941 the Bell Telephone Laboratories were informed that the British group at the Birmingham University had designed and developed a strapped magnetron of improved stability and increased efficiency. About 1 week later the Bell engineers produced their first magnetron of this type. It had an efficiency of 35 percent and a peak pulse power output of 105 kw. Additional tubes were produced, several of which were sent the Radiation Laboratory for testing and experimental purposes. Following this, good high-power 3000- and 10,000-mc. magnetrons were produced in quantity by the Western Electric and other manufacturing companies.81
    Following the development of strapped magnetrons, a new transmitter, using the 700-mc. magnetron and two improved triode modulator tubes, was developed and produced. This transmitter provided a peak power output of about 40 kw. with a pulse of about 2 microseconds duration. It resulted in material increase in reliable range with greatly reduced maintenance. It was interchangeable with the one used in Model FA and was applied retroactively to those equipments. Work on the Model FB fire-control radar was discontinued, and the development of two new models designated FC and FD was instituted.82
    The Model FC was projected for use with fire-control systems against surface targets while the Model FD was for use with 5-inch antiaircraft fire-control systems. As had been planned for in the Model FB, the control console and indicators were remotely located in the directors. Except for the slightly differing requirements of the two fire-control systems and different antennas, both models were identical.83
    A "breadboard model" of the FC was constructed in June 1941 and put on test at Atlantic Highlands with an antenna modified to permit lobe switching in two planes. Its performance was superior to that of Model FA in every detail.84
    The first Model FC equipments were delivered in October 1941 and were installed in the forward and after main battery directors of the U.S.S. Philadelphia during that month. Prior to 7 December 1941, 10 of these equipments had been delivered and were either installed or in process of being installed.85
    The first Model FD equipment was completed during August 1941 and assembled for test at Atlantic Highlands. On 28 August, an aircraft was tracked out to a distance of 24 miles. On this date it was decided that this equipment would be installed in the U.S.S. Roe in conjunction with the first installation of gun director, Mark 37. This installation was completed prior to 22 September and on that date the U.S.S. Roe put to sea. Since this was the first antiaircraft fire-control radar installed in a combatant vessel, much interest was evinced and many high-ranking officers and scientists were embarked.86
    The performance of the equipment was good in range and train. Position angle data was poor at long ranges but improved as the targets approached. It was not realized until later that the water reflection caused this rather than malfunction of the equipment.87
    The only Model FD installed prior to our entry into the war was the one installed in the U.S.S. Roe. Delivery of production equipment did not begin until December 1941.88

12.  WARTIME  DEVELOPMENT  OF  RADAR  UNDER  DIRECTION  OF  OFFICE  OF  SCIENTIFIC  RESEARCH  AND  DEVELOPMENT

The deterioration of the world political situation in 1940 brought about a tremendous expansion of our defense forces. The war in Europe had increased in tempo on the ground, at sea, and in the air. British and German scientists were engaged in a total war, each endeavoring to produce more deadly weapons and to perfect better systems of defense. In the United States the military services were busily engaged in expanding their forces and in training inexperienced personnel. Neither service possessed sufficient scientific personnel to conduct the research essential to keep our defense systems and techniques at the level of those of the major belligerents.
    Scientists became deeply concerned because of this. At the suggestion of Dr. F. B. Jewett, President of the American Academy of Sciences, Franklin D. Roosevelt, by Executive order signed 27 June 1940, established the National Defense Research Committee. The mission of this committee was
to correlate and support scientific research on the mechanisms and devises of warfare.89
About one year later this Committee was integrated into and became the operating body of a larger and independent organization, the Office of Scientific Research and Development, under the leadership of Dr. Vannevar Bush.
    The Army and Navy were enabled to turn over to scientists, mobilized by the Committee, many problems of a long-range nature as well as a large number of those of uncertain possibilities requiring considerable basic research. One of those, involving radar and radio communications, was that of utilizing the microwave portion of the radiofrequency spectrum. One of the first acts of the Committee was to establish, in July 1940, a Microwave Committee under Dr. Alfred L. Loomis, who had been, for several years, experimenting with the use of this portion of the frequency spectrum at his private laboratory.90
    At about this time an agreement was reached between the United States and Great Britain for the exchange of scientific information of military nature. As previously mentioned, in September 1940, the British technical mission arrived in Washington for the purpose of effecting such exchanges.
    On 12 October, the British technical mission suggested that the United States undertake the development of two urgently required radar systems, a microwave aircraft interception equipment and a microwave antiaircraft fire-control equipment. The suggestion was approved by the Microwave Committee. The Radiation Laboratory, under the administration of the Massachusetts Institute of Technology and staffed by physicists from various universities, was established to develop these systems. It commenced operations in Cambridge, Mass., early in November 1940, under the direction of Dr. Lee A. DuBridge. All available information on the radar developments of the British and American military services, the British scientific effort, and of the Bell Telephone Laboratories was made available to this Laboratory. With basic research completed and the magnetron available, the assigned task was not an impossible one. The Laboratory quickly assumed the leadership in the development of microwave radar equipment.
    In order to speed up the development of the airborne interceptor equipment, the National Defense Research Committee contracted with several manufacturers to assist in the development of components. Military hangar facilities were provided at the East Boston Municipal Airport with both military services contributing aircraft for experimental purposes. In January 1941, the Radiation Laboratory obtained echoes from its first microwave equipment using magnetrons provided by the Bell Telephone Laboratories. On 18 March, a laboratory model was tested in a B-18 airplane where it was discovered that the equipment was very effective in locating ships at sea. Prior to the end of May it appeared sufficiently promising to warrant turning it over to the Radio Corp. of America to be engineered for production. By the end of 1941 an airborne microwave set (ASV) for detection of surface vessels had been satisfactorily developed and was ready for production.91
    A microwave surface search radar was developed concurrently with the ASV. In the late spring of 1941 a "breadboard model" of this equipment, equipped with the Naval Research Laboratory plan position indicator, was installed and successfully tested in the U.S.S. Semmes, an old four-stack destroyer. The results obtained led the Navy to award its first production contract for microwave equipment on 30 June 1941. This was the SG radar.
    Prior to the end of May 1941 the completely automatic tracking of aircraft had been accomplished by a prototype of the microwave aircraft interception equipment and it appeared to be sufficiently promising to warrant its being engineered for production. By December 1941 a prototype model of Laboratory-designed harbor-defense radar equipment was in operation at the harbor entrance control post at Boston.92
    By the beginning of 1942 an enormous program of microwave radar development was underway in which the laboratories of commercial companies, universities, the Armed Forces of both the United States and Great Britain, and the Office of Scientific Research and Invention all played a cooperative and vital part. By the end of 1943 this new equipment was in large-scale production and was replacing the 500-700 mc. equipments which earlier were installed on our ships for fire control.

___________________
    1 In narrating the history of radar it was first thought best to divide it into chapters on search radar, fire-control radar, and airborne radar. As the writing progressed it was found that this approach was confusing. The history of radar is therefore contained in this chapter and an attempt is made to provide a chronological narrative. With the excellent records of the naval bureaus, the assistance of Dr. R. M. Page, of the Naval Research Laboratory, the report of the Joint Board on Scientific Information Policy, and the published reports of the companies available, the author endeavors to credit the contributions of individuals, companies, and laboratories whenever they can be substantiated.
    2 Infra, Chap. XXXVI.
    3 Bown, "Ships, Machinery and Mossbacks," p. 138.
    4 A. Hoyt Taylor, "Radio Reminiscences: A Half Century," Naval Research Laboratory report, p. 363.
    5 Chief of Naval Operations multiple-address letter, dated 18 Nov. 1940, serial 069120.
    6 Joint Board on Scientific Information Policy, "Radar, a Report on Science at War," Washington, Government Printing Office, 1945, p. 9.
    7 Ibid., p. 4.
    8 Memorandum, dated 27 Sept. 1922, commanding officer, Naval Air Station, Anacostia, D.C., to Chief of the Bureau of Engineering.
    9 A. Hoyt Taylor, op. cit., p. 267.
    10 Letter, dated 5 Nov. 1930, Naval Research Laboratory, file C-F42-1/67 (E4222).
    11 Bureau of Engineering Problem Specification No. Bl-1, dated 25 Nov. 1930.
    12 A. Hoyt Taylor, op. cit., pp. 268, 269.
    13 Ibid., pp. 269, 270.
    14 Statement of Dr. R. N. Page, Naval Research Laboratory, to the author on 15 Apr. 1959.
    15 Joint Board on Scientific Information Policy, op. cit., p. 5.
    16 Letter, dated 19 Jan. 1933, Director, Naval Research Laboratory to Chief of the Bureau of Engineering, file C-S67/43 (4972).
    17 Buford Rowland and William B. Boyd, "Navy Bureau of Ordnance in World War II," Washington, Government Printing Office, 1953, p. 418.
    18 A. Hoyt Taylor, op. cit., pp. 306, 307.
    19 Ibid., pp. 293, 294.
    20 "Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 1, p. 10.
    21 A. Hoyt Taylor, op. cit., pp. 270, 271, 295.
    22 Letter, dated 15 Sept. 1933, Naval Research Laboratory to the Chief of the Bureau of Ordnance.
    23 Letter, dated 9 Sept. 1935, Director, Naval Research Laboratory, to the Chief of the Bureau of Engineering, file C-49-4/ENO WF-2.
    24 Statement of Dr. R. M. Page, Naval Research Laboratory, 11 Sept. 1961.
    25 Letter, dated 29 May 1936, Director, Naval Research Laboratory, to Chief of the Bureau of Engineering, file C-49-4/E08 (W5-2S); statement of Dr. R. M. Page, Naval Research Laboratory, 11 Sept. 1961.
    26 Letter, dated 12 June 1936, Chief of the Bureau of Engineering to the Director, Naval Research Laboratory, file C-S/67/36 (6-10-W9).
    27 Joint Board on Scientific Information Policy, op. cit., pp. 5-6.
    28 Letter, dated 18 Jan. 1937, Chief of the Bureau of Engineering to Director, Naval Research Laboratory, file C-F42-1/69.
    29 Joint Board on Scientific Information Policy, op. cit., p. 6.
    30 A. Hoyt Taylor, op. cit., p. 300.
    31 Ibid., p. 303.
    32 Statement of Mr. J. W. Smith, of the Bell Telephone Laboratories.
    33 Conference Report, dated 16 July 1937, Director, Naval Research Laboratory, file C-S67/36.
    34 Statement of Mr. J. W. Smith, of the Bell Telephone Laboratories.
    35 Statement of Dr. R. N. Page to the author on 14 Apr. 1959.
    36 Naval Research Laboratory Records of Consultive Services, dated 27 Apr. 1938, 19 Sept. 1938, and 23 Sept. 1938.
    37 Letter, dated 18 Nov. 1944, Eitel-McCullough, Inc., to Radiation Laboratory, Massachusetts Institute of Technology.
    38 Record of conference held at Bureau of Engineering on 24 Feb. 1938 ("Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 2, p. 9).
    39 A. Hoyt Taylor, op. cit., pp. 324-328.
    40 "Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 2, p. 22.
    41 A. Hoyt Taylor, op. cit., pp. 324-328.
    42 Ibid., pp. 328-332.
    43 Ibid., p. 335.
    44 Letter, dated 19 Dec. 1938, Chief of the Bureau of Engineering to the Chief of Naval Operations, serial 292.
    45 Letter, dated 24 Mar. 1939, Commanding Officer, U.S.S. New York, to Commander, Atlantic Squadron, file BB34/S67/(71); "The First 25 Years of the Naval Research Laboratory," NavExos P-249, p. 47.
    46 Letter, dated 24 Mar. 1939, Commanding Officer, U.S.S. Texas, to commander, Atlantic Squadron, file BB35/S67/(296).
    47 Statement by Dr. R. N. Page to the author on 14 Apr. 1959; letter, dated 8 May 1939, Chief of Naval Operations, file S-S67/36 Op-20-E/AB.
    48 A. Hoyt Taylor, op. cit., p. 336.
    49 A. Hoyt Taylor, op. cit., p. 336; serial No. 1 was installed in the U.S.S. California on 7 Aug. 1940. Following the damage suffered by that vessel on 7 Dec. 1941, it was installed at the Army Base, Oahu, T.H.
    50 "An Administrative History of the Bureau of Ships During World War II," undated and unpublished manuscript, p. 252.
    51 A. Hoyt Taylor, op. cit., p. 347.
    52 Ibid.
    53 Ibid., p. 348.
    54 Ibid.
    55 Letter, dated 12 Oct. 1944, Bureau of Ships, Serial C-916-9229.
    56 A. Hoyt Taylor, op. cit., p. 349.
    57 Ibid., pp. 365-366.
    58 Ibid., p. 365.
    59 Ibid., pp. 367-369.
    60 Ibid., pp. 369-370.
    61 Ibid., p. 367. Statement of Dr. R. M. Page, Naval Research Laboratory, 11 Sept. 1961.
    62 Board on Scientific Information Policy, op. cit., p. 5.
    63 Ibid., pp. 4-5.
    64 A. Hoyt Taylor, op. cit., pp. 298, 299.
    65 Joint Board on Scientific Information Policy, op. cit., p. 6.
    66 Joint Board on Scientific Information Policy, op. cit., p. 17.
    67 Ibid.
    68 Ibid., p. 29.
    69 "Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 3, pp. 1-4.
    70 Ibid., pp. 4-7
    71 Ibid.
    72 Ibid.
    73 Ibid., p. 8.
    74 Letter, dated 20 Aug. 1941, Commanding Officer, U.S.S. Wichita, to the Chief of the Bureau of Ships.
    75 "Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 3, pp. 8-11.
    76 Ibid., ch. 5, pp. 1-4.
    77 Statement of Dr. R. N. Page to the author on 14 Apr. 1959.
    78 "Bureau of Ordnance Source Book on the History of Fire Control Radar," ch. 4, p. 8.
    79 Ibid., pp. 8-9.
    80 Ibid., pp. 9-10.
    81 Ibid., p. 10.
    82 Ibid., ch. 4, p. 9; ch. 6, p. 2.
    83 Ibid., ch. 6, p. 1.
    84 Ibid., p. 6.
    85 Ibid., p. 8.
    86 Ibid., p. 6-7.
    87 Ibid., p. 7.
    88 Ibid., p. 8.
    89 Joint Board on Scientific Information Policy, op. cit., p. 9.
    90 Ibid.
    91 Ibid., p. 10.
    92 Joint Board on Scientific Information Policy, op. cit., p. 11.
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