The long road followed by naval history is studded with innumerable milestones each of which marks some noteworthy advance in the technique of sea warfare. At longer intervals can be seen the comparatively few tall monuments to those fundamental developments which mark the beginning of new epochs—the cannon, the galleon, the steam engine, the torpedo, the submarine, and the aircraft. Amongst these must surely be the introduction of shipborne radar at the beginning of World War II.
The characteristic of radio waves upon which radar was founded, namely that such waves on striking a solid object—more specifically a metallic one—were reflected, was appreciated from the earliest days of radio development. In 1886, reflection was demonstrated by the German scientist Heinrich Hertz. In 1922, Guglielmo Marconi, addressing the American Institute of Radio Engineers, said, “In some of my tests I have noticed the effects of reflection and deflection of these [radio] waves by metallic objects miles away. It seems to me that it should be possible to design apparatus by means of which a ship could radiate . . . rays which, if coming across a metallic object such as another steamer or ship, would be reflected back to a receiver screened from the local transmitter on the sending ship and thereby immediately reveal the presence and bearing of [other] ships.”
Nevertheless, Marconi took no serious steps to put his theory into practice; nor was he really advocating radar, as he did not visualize measuring the target’s distance. Similarly, when two American research scientists, A. Hoyt Taylor and Leo C. Young of the Naval Research Laboratory, studying high frequency radio communication across the Potomac in the autumn of the same year, noticed that steamers passing up and down the river interfered with their signals, they drew the attention of the Navy Department to the possibilities of using the phenomenon for detection of ships passing through a patrol line in fog. The “beat” method of radio detection which resulted was still not radar.
Nearer to it were the experiments by a team working under E. V. Appleton in England and by Gregory Breit and Merle A. Tuve in the United States in 1924 and 1925 to calculate the height of the ionosphere by measuring the time taken for radio waves to return to earth after reflection.
These experiments were given no mundane application, however. One other discovery was necessary for this. It took place in 1930 when Leo Young, working with L. A. Hyland, noticed interference with radio waves whenever an airplane was flying in their vicinity. A report on this phenomenon from A. Hoyt Taylor resulted in orders from the Bureau of Engineering to the Laboratory to “investigate the use of radio to detect the presence of enemy vessels and aircraft.” This, of course, still was not radar (radio detection and ranging). But the first steps towards its development were thus taken in the United States.
Progress, however, was negligible during the next three years, at the end of which it was realized that, apart from the fact that neither the range nor the bearing of an aircraft could be determined, the “beat” method, using continuous transmissions, which entailed the transmitter and receiver being widely separated, was unsuitable for shipboard use Then, between 1933 and 1935, the means of overcoming these disabilities suggested themselves at about the same time to radio scientists in Great Britain, France, and Germany, as well as in the United States.
In the United States it was again Leo Young, in 1933, who first hit upon the idea of using extremely short pulse transmissions in the intervals between which the return signals could be received and the time taken to return measured by means of a cathode-ray tube. Success eluded Young and his assistant Robert M. Page, however, until April 1936. Then, with the help of a young engineer, R. C. Guthrie, who had been assigned to the project, experimental equipment was erected —working on a wave length of 10.6 meters —which succeeded in picking up an airplane target at two-and-one-half miles range. This performance was rapidly improved and by June a range of over 25 miles was achieved. It was demonstrated to the Chief of Naval Operations and to the Chief of the Bureau of Engineering, Rear Admiral Harold C. Bowen, at whose request the project was now given the highest priority.
By April 1937, an experimental radar set working on a wave length of one-and-a-half meters had been installed in the destroyer Leary for trials. Improvements to it resulted in the first really successful shipborne equipment with which planes were followed out to a range of 40 miles. These tests were made with separate transmitter and receiver aerials; but a “duplexer” to enable a single aerial to be used for both functions was perfected in February 1938 and the resultant radar set, known as XAF, was installed in the battleship New York in December of that year.
The secret of pulse radar was now released to industry and the Radio Corporation of America produced its first set (CXZ), working on 80 centimeters wave length, which was fitted in January 1939 in the Texas. When this proved not nearly as successful as XAF, R.C.A. then constructed six of the latter, designated CXAM, which were installed during 1940 in the battleship California, the carrier Yorktown and the cruisers Chester, Chicago, Northampton, and Pensacola. Further improvements resulted in the CXAM-1 which was fitted in all the other prewar carriers, in five battleships and the cruiser Augusta. The CXAM set had surface warning as well as plane detection capability and, as installed in the New York, was found to be able to follow the flight of 14-inch shells and record their splashes. It would seem to have been capricious in this function, but as an air warning set it was excellent, and in the Battle of the Coral Sea the Lexington’s set gave warning of the approach of enemy formations at 68 miles.
By this time, radar had been born in Europe, also. Its period of gestation had been shorter, particularly in Britain. In January 1931, two British scientists at the Signals Experimental Establishment,—W. A. S. Butement and P. E. Pollard at Woolwich—had succeeded in recording the first planned radar echoes at a range of about 100 yards, using pulsed radio transmissions. Yet, their ideas were rejected by both the War Office and the Admiralty and it was not until the beginning of 1935 that work on radar was first undertaken by Robert Watson-Watt, then Superintendent of the Radio Department of the National Physical Laboratory. This came about as a result of Watson-Watt being consulted by the Air Ministry with regard to what was popularly known as a “death-ray.” He quickly disabused his enquirers of the feasibility of such a device but, with his assistant, A. F. Wilkins, he at once turned to the study of “radio-detection as opposed to radio-destruction.”
Within one month they had rigged up an experimental receiver mounted on an automobile with which they successfully recorded the passage of an aircraft flying along the radio beam transmitted by the radio station at Daventry. The result was that £10,000 was allocated for further research and a research station was set up at Orfordness. By 24 July 1935, using a transmitter working on a wave length of 26 meters, aircraft were being detected and tracked at ranges up to 40 miles.
The immediate result of this was the decision by the Air Ministry to erect a coastal chain of radar stations. These used a wide beam transmission—a “flood-lighting” system—on a wave length of 12 to 13 meters, requiring very large antennae and masts 250 feet high, both of which were unsuitable for use on board a ship. Radar development, being under the auspices of the Air Ministry, was at first focused mainly on production of shore-based equipment for detection of aircraft. In the division of tasks in the field of radio research, however, the naval establishment, H.M. Signal School (later re-named Admiralty Signal Establishment) was responsible for the development of radio tubes. The Royal Navy thus became drawn into the research taking place, and in August 1935, the Signal School turned to exploration of shorter wave lengths of about one-and-one- half meters.
Considerable research work resulted in tubes giving greatly increased power. Nevertheless, it was not until towards the end of 1936 that a first experimental apparatus was installed on board the minesweeper Saltburn. Results were disappointing, partly owing to the difficulty of producing sufficient transmitting power at the shorter wave lengths. At the end of 1937, therefore, when C. E. Horton took charge of the Admiralty’s radar experimental work, it was decided to concentrate on a set transmitting on seven meters, the longest wave deemed practical for which a useful aerial system could be fitted to a masthead.
The result was the first operational British naval radar equipment—Type 79Y—which, with a transmitter output of 15 to 20 kw., was fitted in August 1938 in the cruiser Sheffield, a second set being later fitted in the battleship Rodney. With it, aircraft at 10,000 feet were detected at a range of 53 miles. An improved set—79Z—fitted in the AA cruiser Curlew a year later made use of the newly developed “thoriated” tubes—in which thorium was incorporated in the filament—to develop transmitter power of 70 kw. Orders for 40 similar sets for the Fleet were placed. When war broke out in September 1939, both the Rodney and the Sheffield reported successful plotting of enemy aircraft and when air attacks on Scapa Flow developed early in 1940, the Curlew was able to give warning of raids at a range of more than 60 miles.
The main effort in Great Britain had thus been concentrated up to this time on radar for plane detection, partly because research was under the auspices of the Air Force, but also because the air detection problem was more easily solved than that of surface detection which required the use of shorter wave technique. As a consequence, when war broke out, only four radar sets were shipborne, all of Type 79Z. Work was in hand, however, to produce a multipurpose set with surface-warning and ranging capabilities as well as air- detection. It was felt that a 50-cm. wave length was likely to give the best results; but its development depended on further improvements in tube technique; 1,000 kw. was available on three meters; time was pressing; so the next set to be produced to serve the triple function of long-range warning, anti-aircraft range-finding and main armament rangefinding was the 3-meter Type 281, the first of which was fitted in the cruiser Dido in September 1940, the next in the batdeship Prince of Wales in January 1941. Its performance against aircraft was good, medium and high aircraft being detected at 60 to 110 miles range. Surface warning performance was moderate, a battleship being detectable at 11 miles.
French scientists also had conceived the idea of radar. The basic theory of using the interference with radio transmissions to detect the passage of aircraft in the vicinity of a transmitter was first argued by M. Pierre David, Engineer of the Telegrafie Militaire and member of the National Radioelectric Laboratory. With no funds for experimentation at his disposal, however, he could arouse little interest in his theory, until the publication in March 1933 of the observations of A. Hoyt Taylor in America. During 1934, experiments at Le Bourget airfield confirmed the American experience and resulted in the setting up of a number of metric-wave, continuous-transmission radar stations or barrages electromagnetiques as part of the defenses of the major naval ports.
Meanwhile, M. Henri Gutton, in association with the Compagnie Generate de T. S. F., had been experimenting with a 16-cm. wavelength, primarily with the aim of producing an iceberg detector for use on board transatlantic liners. The first experimental set was installed in the liner Oregon in 1935 and another in the Normandie at the end of that year. They were able to detect small ships at a range of about two miles and their change of relative bearing could be followed. But with continuous transmission the actual range could not be measured and, furthermore, there was much interference from the ship’s superstructure.
During the next three years, search for a suitable generator of power at high frequency finally resulted in a 16-cm. pulse transmitter with a peak power of 10 watts and a receiver with a cathode ray tube display. In 1939, a magnetron with resonant segments and thoriated filament was developed which gave a peak power of 300 watts. From the experimental stations at Sainte Adresse, near Le Havre, and at Brest, detection of mediumsized ships up to six miles, with a range accuracy of 100 yards was achieved.
With the outbreak of war in September 1939, the more advanced techniques in use in Britain were learned and applied resulting in a 16-cm. magnetron giving half a kilowatt or more peak output. This was a considerable advance on anything achieved elsewhere on such a high frequency and, fortunately, an example was passed to the British General Electric Company before experiments were halted and all material destroyed on the German advance into France in 1940. The French technique thus shared proved of considerable value to G.E.C. in its development of the revolutionary 10-cm. magnetron described later.
The main French effort, however, continued to be directed to air-warning radar using metric waves and, in conjunction with British technique, manufacture was begun in 1939, of sets working on six-and-one-quarter meters which, installed in a number of shore stations, gave excellent results against aircraft.
In view of the virtual immobilization of the French Navy during the next three years, it is not surprising that little in the direction of development of shipborne radar took place. Nevertheless, in February 1941, a metric wave set was installed on board the Richelieu at Dakar. Compared with those by that time under development in Britain and the United States, it was primitive, employing separate transmitting and receiving antennae. However, it achieved detection of aircraft at 50 miles and of ships at six to 12 miles.
While in Britain, France, and the United States, radar had been primarily developed for plane detection with surface detection arriving as a bonus, the opposite had been the case in Germany. There, the first successful transmission and reception of a radar signal had been achieved in March 1934 when a 50-cm. set constructed by the firm of GEMA for the Naval Signals Experimental Establishment had obtained reflections from the liner Hessen in Kiel harbor at a range of about 100 meters.
From this humble beginning, by October of the same year, GEMA, with a 50-cm. set and a transmitter of 50-watt output mounted on a turntable at the top of a 40-foot tower, was able to detect a small target vessel at a range of six-and-one-half miles.
Ranging in these early sets was by means of tone-modulated continuous signals; but, as in the United States and Britain, the idea of pulsed transmissions was now conceived and in March 1935, the first radar detection by this method was obtained at a range of five-and-one-half miles. By the end of 1935, the range had increased to eight miles with a bearing accuracy of two degrees.
GEMA had in the meantime been experimenting on a wave length of 13 cms. with fairly high-powered pulsed transmitters and had obtained detection ranges of two-and- one-half miles. Whether these experiments would have resulted in the crucial discovery of the means of obtaining really high power transmissions in the 10-cm. band which was to revolutionize American and British radar will never be known. In October 1935, they were discontinued at the express wish of the Naval Signal School, against the protests of the firm, to concentrate on the apparently superior 80-cm. band. Thus it was that the first radar sets fitted for trials, on board the Admiral Graf Spee, the cruiser Konigsberg, and the torpedo boat G.10 in the summer of 1936 were 80-cm. sets.
In the following year, during maneuvers off Swinemtinde, these sets proved quite successful against surface targets, the liner Hessen being detected at 17 miles, the cruiser Konigsberg at five to eight miles and even torpedo boats at 11 miles. In the summer of 1938, equally good results were obtained from the same sets on AA mountings, ranges of 60 miles being obtained on formations and single aircraft.
Indeed, these results may be said to have been unfortunately good from the point of view of the German Navy. For they came to the ears of Reichsmarschal Hermann Goering who at once demanded 1,000 AA sets from GEMA for the Luftwaffe, with the results that the firm had to be vastly expanded; any efforts that might have gone to exploration of shorter wave lengths had to be concentrated on mass production of 80-cm. sets to which the German Navy was thereafter committed.
When war broke out, only the Graf Spee and the Konigsberg had been fitted, but 80-cm. sets were provided soon afterwards in the Scharnhorst and the Gneisenau, and these two battlecruisers made good use of them early on 9 April 1940 to avoid being surprised by HMS Renown off the north Norwegian coast in thick weather. Low clouds, rain and snow squalls were making visibility to the westward very poor when radar contact on a bearing of 220° was made at 0430 by the flagship Gneisenau. Action stations were ordered so that when the Renown, which had no radar but from which visibility towards the dawn was fairly good, opened fire, the German ships were not long in replying. Again on 8 June, when the carrier Glorious was encountered and was screened by smoke from her attendant destroyers, the Scharnhorst and the Gneisenau were still able to engage her, using radar ranges and bearings. It was not possible to detect shell splashes, but by ranging back and forth either side of the radar range, hits were obtained which crippled and eventually sank the carrier.
The same 80-cm. sets were soon fitted in most of the larger German ships as well as their destroyers. In the former, the apparatus was housed usually at the top of the foremast on rotating stands to the outside of which was fixed the antenna. In smaller units, special cabins were erected on the bridge above which the rotating antenna protruded. Increase in transmitter output, developed soon after the outbreak of war, raised detection range to 75 per cent of the optical range. The cruiser Hipper made good use of her radar to evade the British patrols in the 25-mile-wide Denmark Straits to the northwest of Iceland, when she broke out into the Atlantic in December 1940, as did the Scharnhorst and the Gneisenau following the same route in the next month.
German warships were thus much better equipped with regard to surface warning radar than the British during the first two years of war, though in air warning and air ranging the position was reversed.
In pursuit of a radar set for gun control, a group of British scientists in close co-operation with the General Electric Company had been working on a 50-cm. set since 1938. Trials with an experimental set rigged up aboard the destroyer Sardonyx in 1939 proved promising and early the next year an experimental set was installed in the Nelson with antennae on the main gun director. Such good results were obtained that 200 sets of this Type 284 were at once ordered and the first production model went to sea in September 1940, mounted in the Hunt-class destroyer Southdown.
Though results were not as good as expected —those recorded by the Nelson had been abnormally good owing to “anomalous propagation”— detection ranges of 18,000 yards on a cruiser and 12,000 yards on a destroyer were obtained. This set proved its value when it enabled the cruiser Suffolk to detect and shadow the Bismarck when the latter broke through the Denmark Straits into the Atlantic. Given an increased power of 50 kw. and modified to make use of a single antenna for transmitting and receiving, Type 284 continued to be used and developed during the war and achieved its most. notable success when, at 0450 on 26 December 1943, the battleship Duke off York opened fire in the black Arctic night on the Scharnhorst at 12,000 yards and obtained a hit with her first salvo. In the subsequent gun duel fought at ranges up to 20,000 yards using radar control, out of 52 salvoes fired by the Duke off York, 31 were straddles.
Nevertheless, a year after the outbreak of war only radar sets for air warning and rangefinding—AA and LA—were being fitted in British warships and these only in cruisers and above. Although in the background, under Admiralty auspices, research that was to result in the greatest breakthrough in the radar field was going on, no general surface warning set was being developed. The major production effort being an Air Ministry responsibility, it was concentrated largely upon production of airborne sets. It was with an adaptation of one of these, the one-and-one-half-meter air-to-surface set (ASV), that the Navy at first had to content itself.
In August 1940, when a naval Walrus amphibian airplane was testing its ASV set on the slipway at Lee-on-Solent, it was noticed that shipping offshore was being detected at a range of five miles. These results were brought to the notice of the Signal School with a proposal that the same set should be fitted in destroyers. The problem of devising an antenna system that would give sufficient gain while still being light enough for a destroyer’s mast, and of fitting both the receiving and the transmitting antennae on one mast, was tackled and a number of destroyers employed on East coast convoy protection were equipped.
Though the fixed “mattress” antenna gave a look-out capability only from fine on the bow to just abaft the beam on either side and only very rough bearings could be obtained without swinging the ship, useful results were obtained against German E-boats, and the Admiralty decided to fit a large number of destroyers both on the East coast and in the Western Approaches. It was not until mid- 1941 that these sets were being delivered in any quantity. Their performance cannot be described as satisfactory though it was with one of them that the first recorded detection of a German U-boat was made in March 1941 when the U-100, commanded by the “ace” captain, Joachim Schepke, was detected at a range of one mile by the destroyer Vanoc which jammed and sank the U-boat.
The need for a set with a revolving aerial was keenly felt and eventually a Type 291 on a one-and-one-quarter-meter wave length was produced with both surface and air warning capabilities. Nevertheless, it had been long appreciated that for surface warning radar, particularly on small targets such as a U-boat, a set operating on a much shorter wave length was likely to give the best results; furthermore, it would enable a very small antenna to be used.
Research with the aim of obtaining useful results in the region of 10 cms. had been begun by the naval Signal School Laboratory as early as 1938. The problem centered primarily on the production of suitable tubes, particularly a transmitter tube to generate sufficient power at such a high frequency. Fortunately, in view of the absorption with meter-wave technique by the Air Ministry scientists under Watson-Watt at this time, development of tubes was an Admiralty task. Thus, it was a team of scientists headed by Mark Oliphant of Birmingham University working under Admiralty auspices that, in February 1940, made the dramatic breakthrough that was to place the war-winning weapon of centimetric radar in the hands of the Allies.
The scientists directly responsible were H. T. Randall and H. A. H. Boot. In his The Pulse of Radar, Sir Robert Watson-Watt* has described how these two men hit upon the idea of the resonant cavity magnetron. In their search for “many watts on a few centimeters,” their thoughts had played on the “magnetron,” a well-known but not very effective form of transmitting tube invented by A. W. Hull of the American General Electric Company in which an electro-magnet was incorporated. They had also studied the characteristics of the resonant cavity or “rhumbatron” used in the “klystron,” another form of transmitting tube invented by the American scientists Hansen and Varian at Stanford University.
Randall’s and Boot’s stroke of genius was to conceive of bringing the magnetron and the rhumbatron together to combine in the resonant cavity magnetron. As Watson-Watt puts it, “Jets of thought played over resonant cavities in the mind, and then one day, Randall and Boot sat down quietly after luncheon—and arose for laboratory tea with a few sheets of paper in their hands. The work of a single afternoon had gathered into a single note, which I like to call the Magnetron Memorandum, the harvest of many sowings, from many sources, in the fertile ground of two acute minds. . . .
“Some three months of machining, of manufacture of the very considerable ancillary equipment, big electro-magnets, high- tension rectifiers and so on, and bench assembly, followed. . . . On 21 February 1940 the new device was successfully operated. The results were spectacular ... it was clear that the output power was not around the few watts of the past, not the previous world record of a few tens of watts, but very nearly half a kilowatt.”
The work of perfecting and redesigning this device for practical use was undertaken in co-operation with the G.E.C. research laboratory at Wembley. Within three months it was completed, delivering 50 kw. of peak power at a wave length of 9.1 cm. (In May 1941, the parts for a 10-cm. magnetron designed to deliver peak powers of 3 million watts were produced.)
Delivered to the Air Ministry Research Establishment at Swanage and operated in conjunction with another device specially developed under the supervision of Robert Sutton of the Admiralty Signal Establishment —the Velocity Modulated Tube for reception of 10 cm.—a radar set was assembled which when demonstrated to Admiralty scientists in November 1940, produced striking results on a submarine target.
The way was now open for production of the first effective surface warning set for fitting in convoy escorts and in March 1941 it was fitted in the Flower-class corvette Orchis. Results were so good—5,000 yards on a fully surfaced submarine, 2,800 yards on a trimmed- down submarine and 1,300 yards on eight feet of periscope—that 350 sets were at once ordered.
Several important developments further improved this set. The revolving antenna was gyro-stabilized; an improved magnetron and a reduced pulse length increased the output power to 100 kw., giving detection ranges of 8,000 yards against a U-boat. The problem of passing this increased power from the magnetron to the antenna led to the introduction of the wave guide, the transmission of the electro-magnetic waves through an empty metal tube with reflectors to guide them round any corners in the tube. The theory of the wave guide had been long known but it had only become a practical proposition with the introduction of the high frequencies of the 10-cm. band.
The tactical use of radar was at the same time greatly simplified by the introduction of the Plan Position Indicator (PPI). This device, which was first developed by British scientists in 1940 for use with airborne radar at the very time that a similar device for use with the naval CXAM set was being developed in the United States, consisted of a cathode ray tube with an after-glow characteristic, the trace of which radiated from the center and rotated synchronously with the antenna.
The plan picture of the area in the vicinity of a ship thus provided was of immense value in night operations. Warning was provided of the approach of an enemy or other unit, which, without an intricate plotting organization was about the limit of the information to be gained from the simple “A” scope of previous radar equipment. Moreover, when action was joined it was possible to keep track and distinguish friend from foe, to maintain an assigned station and to detect any newcomers on the scene, such as a surfacing submarine—a particularly valuable capability in convoy defense operations.
With the equipping during 1942 of the majority of escorts with the 10-cm. radar and the PPI, the way was open, in conjunction with the other newly developed device—the High Frequency Direction Finder—for the great showdown in mid-Atlantic with Admiral Doenitz’ “Wolf Packs.” The result was the U-boat massacre of May 1943 leading to Doenitz’ admission of defeat in the Battle of the Atlantic.
To complete the picture of radar development in Europe, the achievement of M. Gutton in France with his 16-cm. equipment must be noted. Experiment began again at Toulon in 1941 after the French capitulation, and a magnetron was produced giving a peak output of 4 kw. and a fairly good performance. None of these sets ever became shipborne, however, and all of them were destroyed on the German occupation of Toulon in November 1942.
Having rounded off the European end of the naval radar story, we must now return across the Atlantic where, since the autumn of 1940, the great resources, scientific and industrial, of the United States had been directed to massive exploitation of the breakthrough into the centimetric radar field.
In June of that year, at the instigation of Vannevar Bush, chairman of the National Advisory Committee for Aeronautics, the leading figures in American science had been gathered together to form a National Defense Research Committee of which Division D, headed by K. T. Compton, President of M.I.T., concerned itself with detection, controls and instruments. Sub-section D.1. which later became Division 14 of N.D.R.C., headed by Alfred L. Loomis, a New York lawyer and a pioneer in the field of micro- waves, was set up to study the application of microwaves (radio waves 10 cm. or less in length) to detection devices.
This Section, working at the Loomis Laboratories in Tuxedo Park, New York, soon came up against the apparently impenetrable barrier shielding the mystery of production of an equated transmission power at such frequencies. The best that they were able to achieve was a klystron delivering 10 watts at 10 cm., so that work on development of a surface warning radar for the U. S. Navy was being concentrated on a 50-cm. set which later became the S.C., the set used in the early stages of the Pacific War. With an air detection as well as a surface-warning capability, it was more effective in the former.
For surface detection it was temperamental as was demonstrated during the disastrous Battle of Savo Island, when the U. S. destroyers Blue and the Ralph Talbot, each equipped with an S.C. radar set, failed to detect the enemy’s cruiser and destroyer force passing at a range of a couple of miles.
In September 1940, a British scientific mission headed by Sir Henry Tizard arrived in the United States with the object of exchanging scientific information. Received with a welcome not untinged with suspicion, the British scientists discovered the “Open Sesame” to the confidence of their hosts when they produced on 29 September at Loomis Park the 9.1-cm. resonant cavity magnetron “the most valuable cargo ever brought to our shores” and “the most important item in reverse lend-lease” as James Phinney Baxter, III, has described it in his book, Scientists Against Time. American interest flared as the epoch-making nature of the magnetron was appreciated. Within a few days approval was obtained for the principle to be disclosed to industry and the Bell Telephone Laboratories were selected to manufacture the magnetron.
The barrier to progress in microwave research had been dramatically breached. It was decided to set up a central laboratory to follow up the break-through. Borrowing a leaf from British practice, it was to be staffed as much as possible by research physicists from colleges and universities. E. O. Lawrence of the University of California undertook the delicate task of recruiting members without being able to tell them in advance the nature of their job. His high reputation in the world of science, however, brought followers flocking to his standard and, on 15 October 1940, Lee A. DuBridge of the University of Rochester was appointed director of the National Radiation Laboratory at M.I.T.
Under the urging of the British Mission, pre-occupied at the time with the necessity to defeat the German air assault on England, it was decided that the Radiation Laboratory should give top priority to a 10-cm. airborne interception set. Given a flying start by the experience with microwave airborne interception of E. G. Bowen, the British Liaison Officer, who was able to draw a block diagram of the component parts needed, and by spreading the work over the leading electronic companies in the United States—Bell, General Electric, Westinghouse, R.C.A., and Sperry Gyroscope—progress was rapid.
By 4 January 1941, the first set was operating and by March it was airborne in a B-18 and performing admirably. In addition to its airborne interception capability, it was found to be very effective in an ASV role, strong echoes being received from a surfaced submarine at a range of three miles from a plane flying at between 500 and 1,000 feet.
It was now adapted for shipboard installation as a surface warning set. In conjunction with the first shipboard PPI it was fitted in the U. S. auxiliary Semmes in May 1941. It was immediately successful and when the U. S. Navy placed a production order with the Raytheon Manufacturing Company the famous S.G. set was born.
This set had its first important combat experience at the night battle of Cape Esperance on 11 October 1942 when the cruiser Helena detected the approach of the enemy at a range of 27,700 yards. Similar sets in the cruisers Salt Lake City and Boise made contact at 16,000 and 14,000 yards, respectively. Unfortunately, none of these ships was Rear Admiral Norman Scott’s flagship. Not for the last time radar by itself in subordinate ships proved to be less than a force commander required for control of a night action. Good communications and a display under the Admiral’s eye were also essential. None of these contacts was reported and in the meantime, unaware of an enemy force on his beam, closing at 20 knots, Scott ordered a counter-march by his force. As a consequence, when the Helena finally got a report through to him, his van destroyers were between his cruisers and the enemy. The confusion that inevitably resulted robbed Scott of what must otherwise have been an annihilating victory.
A similar failure, during the cruiser night action off Guadalcanal on 12 and 13 November 1942, to keep Rear Admiral Daniel J. Callaghan (whose flagship, once again, lacked S.G. radar) informed of the radar picture developing, led to a disastrous outcome to a battle in which the situation initially had been all in favor of the American force. Such bitterly learned lessons, as well as the failure to make the most of the information provided by air warning radar in the early carrier battles, forced the development of the Combat Information Center (CIC) fed by improved radio circuits. By July 1943, S.G. radar with PPI presentation and a CIC had become standard equipment for destroyers and above.
Target identification and gun control by radar had its most spectacular success on the night of 14 and 15 November 1942, when the battleship Washington achieved total surprise on the Kirishima and destroyed her in seven minutes with a storm of fire from radar controlled main and secondary armaments.
Other versions of the 10-cm. radar were developed during 1942 for specialized use, such as the S.J. for surface warning in submarines, all of which had been equipped by early 1943. With this set it was possible to make night torpedo attacks of deadly effectiveness and also to make use of wolfpack techniques.
Though the S.G. set continued to give good service as an air warning radar, it was supplemented by the S.K. 10-cm. set which incorporated the CXAM-1 antenna and a PPI, giving not only a greatly improved performance, but enabling a sophisticated fighter direction system to operate. Still another version of the 10-cm. radar was the S.F. set, intended originally to be a light, compact model for PT boats. Manufactured mainly by the Submarine Signal Company, the first experimental model was tested on board the Tacoma-class frigate Gallup in June 1942, and gave superlatively good results. During development of this set, however, changes in design resulted in a system too heavy and too bulky for the smallest craft as originally intended, and, though no less than 1,655 sets were produced which gave excellent results aboard larger ships, a fresh start had to be made with a set for PT boats. This resulted in the S.O. set, produced by the Raytheon Manufacturing Company, the first production model of which was tested in February 1943. The S.F. set was followed at the beginning of 1944 by the 3-cm. S.U. designed specially for the DE class of ship. Nearly 700 of this most successful set were delivered before the end of the war.
The initial success with 10-cm. sets had inspired scientists of the Radiation Laboratory to explore even shorter wave lengths. The result was the development of 3-cm. sets during 1942, initially for airborne employment in night fighters, which showed such remarkable improvement over 10-cm. equipment that development of a 3-cm. set for direction of night fighters from carriers was also put in hand. A prototype, the S.M., was installed in March 1943 in the Essex-class carrier Lexington. By August 1943, the production version of the S.R. was being installed in all carriers and, with the advent of the Battle of the Philippine Sea, enemy air formations were detected at ranges up to 150 miles.
It is impossible to exaggerate the part that microwave radar played in the achievement of Allied victory in World War II. In every branch of warfare it gave an enormous advantage over the enemy, who continued to be restricted to the far less effective meter wave radar equipment. It was not until a radar was recovered from a British plane shot down in 1943 that the secret of centimeter radar was revealed to the Germans. The German Navy at once recommended the development of it which they had so mistakenly abandoned in 1938. They eventually produced the “Berlin” and later the “Renner” equipments, but neither was ever used operationally.
Few naval officers still active can have had much experience in the days before-radar became as essential a piece of shipboard equipment as the compass. Perhaps only those who knew night action or convoy escort operations without benefit of the magic eye can appreciate the truth of the contention made at the beginning of this article that the introduction of radar comprised one of those outstanding developments that not merely advanced but revolutionized the technique of naval warfare.
* Sir Robert Watson-Watt, The Pulse of Radar (New York: The Dial Press, Inc.).