Chapter 15: Equipment: Elaborations and Developments to V-J Day
Throughout the last two years of World War II the laboratories of the Signal Corps remained large and busy with many tasks, despite the heavy reductions in men and projects effected in 1943 and the transfer of half of their domain to the Army Air Forces in 1944 and 1945. Although the bulk of laboratory effort went into the improvement and engineering support of equipment already in the field, all research and development were not eclipsed.
General Colton, to whom fell the task of accomplishing the 1943 reductions, fended well for Signal Corps research and development activities, so basic to success in modern warfare. His order to the laboratories in December 1943, restricting research in favor of invasion preparations, was required by higher authority and was necessarily the consequence of overriding military operational needs. General Colton well knew that at the center of the laboratories lay a hard core of effort bearing upon future combat needs as well as upon the requirements of the moment. That hard core must not be lost. He therefore forbade any reduction in certain categories of projects: 17 of them at the Monmouth laboratories, 9 at Wright Field—a small percentage of the total sum of projects, but a significant one. All RCM projects, for example, were continued without diminution. Further, in the New Jersey laboratories work continued unabated on radio relay equipment and on the SCR-694, the lightweight field radio intended to replace the SCR-284. General Colton also continued research on quartz crystals (efforts that would lead to synthetic quartz) ; new battery types, especially mercury batteries; and tool, test, and maintenance equipment. At the Aircraft Radio Laboratory nothing was to detract from research on the new, superlatively accurate BTO radars, the AN/APS-15 and APQ-7, or the test equipment under development for 10- and 3-centimeter microwave radars, or the radio-guided bombs. All these developments greatly affected the progress of the war during its last months.1
A Few Examples—From Wire Equipment to Electronic Fuzes
Besides the large variety of RCM equipment, the laboratories worked on many new developments from mid-1943 on—some large, such as the new radio relay AN/TRC-6 employing pulse modulation techniques and the packaged carrier bays used in multichannel wire and radio circuits; others small, but large in significance, forerunners of a future succession of items, ever smaller, but better. Examples were the lip microphone, T-45; the small switchboards such as the 12-pound SB-22/PT and the still smaller SB 18/GT (composed of six plastic adaptor plugs U-4/GT and known as a “vest pocket” board); new field wire WD-1/TT, plastic covered (polyethelene), much smaller and better than W-110-B; the improved and smaller sound-powered telephone TA-1/TT to replace the TP-3, which had proven so valuable in jungle fighting; new methods of winding wire in the high-speed dispenser coils (MX-301/G for W-130, MX-302/G for W-110, MX-306/G for WD-1/TT), which eliminated the use of heavy steel spools or reels and enabled such rapid unwinding, without kinks, that the wire could be run out from a speeding vehicle or even from a low-flying airplane.2
Of great significance too was the small mercury battery. Portable radio sets are no better than their batteries, which often fail. Dry batteries constituted a never-ending problem to the Signal Corps production and distribution services. Needed in the billions,3 yet shortlived, the batteries could not be stored for long whether on supply shelves or in unused equipment, least of all in tropical heat. The typical sal ammoniac paste dry cell remained a problem until 1943 brought relief with the appearance of the RM (Rubin Mallory) cell, whose virtue lay in a pellet of mercury oxide. Though known before, the type was first adapted for the military by the Signal Corps, which built up huge production facilities in order to manufacture the cells in quantity. One-fourth the size and weight of the older sal ammoniac type, with much longer shelf life and several times more electrical output, the RM mercury battery became a large Signal Corps contribution. Produced in the hundreds of millions over the last two years of the war, as BA-38-R, 49-R, 70-R, and 80-R, the batteries powered the universally used “handie-talkies” and walkie-talkies (SCR-536 and 300), as well as the guidon set SCR-511 and the new SCR-694.4
Proximity fuzes, small, fist-sized, expendable radar (or doppler radio) sets of the type used for unrotated missiles such as rockets, bombs, and mortar shells were a concern of the Signal Corps.5 The Aircraft Radio Laboratory developed for use in airborne rockets both a photoelectric fuse, MC-380, and a radar or radio fuze, MC-382. Work on the latter type adapted for bombs followed—AN/CPQ-1 and 2, designed to detonate above foxholes and exposed troops. The MC-382 and AN/CPQ fuzes contained miniature CW (doppler) radar sets, each complete with power supply, transmitter, receiver, amplifier, and an electric detonating circuit, all jammed into a package a few inches in size.6
Missile Controls
For decades, the rocket enthusiasts on both sides of the Atlantic had pored over their notions and hand-built models. Their conservative and conventional scientific brethren regarded the enthusiasts as hardly on the border of respectable science, if not beyond the pale altogether. Solid, sensible citizens ostracized them, but at least did not burn them for their black arts, as their ancestors would have done. But Adolf Hitler, who did almost no man a good turn, catapulted rocket enthusiasts to success and started a new era in the world of science when he gave state approval and, more especially, state funds, to the rocketeers’ dreams.
Before the guided rocket, seeking a target above, came the guided bomb, dropping with the pull of gravity to a target below. The Germans introduced the glide bomb, radio-controlled, with some success in 1943,7 whereupon the U.S. Signal Corps and the Navy undertook to develop similar weapons. Several modes of guidance were possible: (1) a radar in the bomb that would transmit signals and then detect echoes from a target and home on those echoes; (2) a television set in the bomb that would transmit a view of the target ahead to an operator in an airplane above, who in turn would steer the bomb by remote control; or (3) simply a radio control receiver in the bomb that would respond to guiding signals from an observer in an airplane above. The last method was the simplest and this the ARL quickly utilized in the Azon, a 1,000-pound bomb with movable fins that a receiver within could vary in response to signals radioed from the distant observer. Azon could be controlled in azimuth only but could be and was used very effectively against long narrow targets—against
railroad viaducts in Italy and bridges in Burma.8
Thus radio-guided bombs, introduced by the Germans, quickly proved practical. Next would come guided missiles, roaring up under their own power. The need for guided missiles was growing. The reach of antiaircraft guns had attained a maximum, the Army Ground Forces declared in February 1944, asserting that gun projectiles could not knock down stratospheric aircraft or high rockets such as the rumored German V’s. Antiaircraft rockets were needed. The rockets themselves would be an Ordnance responsibility. Guided, they would become missiles, and their guidance would be electronic and therefore a concern to the Signal Corps. General Colton, however, gently braked the AGF appeal. He preferred not to begin work on such controls until Ordnance determined the type of missile and its flight characteristics. Maj. John J. Slattery, formerly a civilian engineer at the laboratories and currently a technical officer in the Washington headquarters, agreed, adding the invariable lament of the laboratories since the 1943 cut—not enough manpower. “The project,” he wrote in April 1944. “appears ... to be desirable for a long range investigation, but one which the Signal Corps should not attempt at the present time due to the limitations of personnel.”9
It should be noted here that the Germans had developed a successful antiaircraft rocket, the Schmetterling 8-117. They expected three hundred in August 1945, production increasing to three thousand a month by December. This missile, SCEL scientists commented late in 1945, “would have profoundly altered the aspect of air warfare, had the war lasted another half year.” The consequences would have been “disastrous,” as Lt. Gen. James M. Gavin put it years later.10 The cavils against rockets and against government research in general were smothered by the eerie scream of Hitler’s first V-2, which struck London with unheard of speed and impact on 12 September 1944.
Meteorology
Meteorology, though it took some of the deepest cuts at the laboratories in 1943, necessarily remained significant. Increasing employment of military aircraft the world over required more and better weather reports. “In more and more complex ways are we committed
now to operations on a worldwide basis,” one authority would write soon after the war, “and more and more do all these techniques depend on precise knowledge of weather.”11 “Weather is a weapon,” commented another. “If left to chance, it may help you and the enemy, hurt both of you, or aid one of you and hinder the other. If it is properly used, the weather can be ... on your side most of the time.” Ill understood and unappreciated, the meteorologists at the end of World War II stood nonetheless, like their fellow scientists and technicians in the communication-electronic discipline, on the threshold of a new era.12
The laboratories of the Signal Corps throughout the last years of the war continued to pursue a variety of meteorological projects. Eatontown Signal Laboratory made improvements in hydrogen gas generators and in the neoprene plastic balloons that the gas lifted aloft to indicate by their drift the direction and speed of the wind or, carrying the radiosonde, to detect other weather factors. On the ground the weather station crews no longer tracked the balloons with the telescopic viewer called a theodolite, but with the meteorological balloon radio direction finder, a device on which the laboratory completed development in 1943 (service test models reached the field by early 1944). The tracker was the SCR-658—sometimes called Rawin for radio wind—a meteorological direction finder whose operator, hand-turning the antenna, could track up to 60,000 feet through darkness or cloud the signals of a radiosonde dangling beneath a soaring weather balloon. In addition to acquiring wind data, the SCR-658 garnered a variety of other weather information. The set included recording equipment, AN/FMQ-1. The recorder printed a continuous record of the weather data that the radiosonde perceived all along its upward course, and that a tiny battery-powered transmitter sent back to earth. The Signal Corps developed a variety of radiosondes. An improved FM version was the AN/AMT-2, able to measure continuously temperature, pressure, and humidity throughout the balloon’s long ascent.13
For Rawin purposes, radar could be used in place of the radio direction finder. In fact, radar measurements of the balloon’s wind drift were more accurate. The weather balloon itself did not return an echo, but metallized paper reflectors could be hung below the balloon. Folded so as to create angular pockets, these corner reflectors of aluminum foil returned very strong radar echoes. The Signal Corps developed not only such reflectors but also the SCR-525 and SCR-825, special meteorological radars, or direction finders, employing the pulse-echo principle of radar.14
SCR-658 trained on radiosonde AN/AMT-2 at launching
Actually, almost any radar could be utilized for Rawin purposes, and all types of sets in the field came to be so used, including even the patriarch SCR-268.15 Among the best, of course, were the SCR-584’s, which troops employed as readily at night or through clouds as during the daylight hours in order to track a corner reflector hung upon a drifting balloon. The oscilloscope operator read off continuously the range, azimuth, and elevation of the soaring target while a crewman plotted the data on the standard Signal Corps plotting board ML-122 in order to compute wind direction and speed. By 1945 the Army Air Forces had allocated more than thirty SCR-584’s to their weather service for Rawin use.16
Rawin would be the primary function of these SCR-584’s, the Air Forces stipulated, but added that the sets would also play a secondary meteorological role—storm detection. Since the earliest use of microwave radars—the SCR-582 and 615 used in Panama in 1943—radar crewmen had noticed how clearly their sets could “see” dense storm clouds at great distances, because the
lofty thunderheads returned clear echoes. The sets were valuable in tropical lands where storms suddenly spring up, and useful wherever weather stations were absent, as over large waters areas, over enemy territory, or over mountain wastes.17
Radar ranges were limited, however, to one or two hundred miles. Something better was at hand, able to detect thunderstorms a thousand or more miles away—the technique called Sferics, which makes use of lightning discharges. A flash of lightning is a very effective radio broadcast, as everyone knows who ever tried to listen to an AM radio program while a thunderstorm rumbled in the vicinity. Sferics (derived from atmospherics, or what the radio listener simply calls static) involves a system of two or more radio direction finders located some hundreds of miles apart but tightly linked by a communications net. The operators take delight in the crackles of static that the ordinary radio public abhors. The Sferics DF men take bearings on the sounds of lightning discharges, coordinate their data, plot the bearings on maps, and locate storms at vast distances. The British were the first to use the technique. Learning of it, the Army Air Forces asked the Signal Corps for Sferics equipment early in 1944. During that year the Eatontown Laboratory (later the Evans Signal Laboratory to which the project was transferred) developed a static or Sferics DF, the AN/GRD-1. The Signal Corps obtained the first development models in October 1944 and in December provided the first complete American Sferics system, four DF’s, plotting equipment, and necessary supplies, enabling the AAF to establish a badly needed installation in the Pacific.18
Besides all the paraphernalia associated with Rawin and Sferics, the Eatontown Signal Laboratory developed further a variety of meteorological sets, large assemblies of equipment mounted in trucks and trailers. The SCM-1 for the Army Air Forces became refined into the AN/TMQ-1; the SCM-9 and 10 for the field artillery became AN/TMQ-4. These complete weather stations, including radiosonde equipment able to determine weather conditions at all levels from the surface to the upper air, were for the benefit of aircraft operation and of artillerymen, who must know the conditions aloft through which large caliber shells pass in order to make ballistic allowances for wind and pressure. The complex sets required crews of several men each. But already the Air Forces was seeking automatic weather stations that could be placed in rigorous locations—on mountain peaks and icecaps, for example—and that could, without a human caretaker, ascertain weather data and transmit the information (radioing it at predetermined intervals for weeks and months on end) to the nearest inhabited post, perhaps hundreds of miles distant. Accordingly, the laboratory developed robot sets
SCM-17, 18, and 19, forerunners of the automatic weather stations of the future.19
In the immediate future, too, the meteorological specialists at the Signal Corps Engineering Laboratories realized, rocketry would require better recording of data and better transmitting of it from greater distances in the sky—telemetering would become the name for these techniques. Weather balloons and their radiosondes would have to strain upwards to greater elevations. Indeed, there would be no end, no ceiling, upon the partnership of meteorology and communications-electronics, as man’s curiosity continued to probe the upper atmosphere and beyond.20
Microwave Radars on the Ground, AN/CPS-1 and 6 and SCR-584
By the mid-course of the war radars were flooding out of the laboratories in an unbelievable variety of types and applications, not only aircraft sets (tail warning radars, airborne range finders, gun layers, Rebecca-Eurekas, and so on) but also ground sets. Among the latter were several versions of LW radars and height finders used to determine the elevation of aircraft.
The Chief Signal Officer strongly believed that there were too many types of ground radar. They had been engendered by extreme pressure and urgency early in the war, and by mid-1944 some of the sets constituted, General Ingles exclaimed, “outstanding examples of non-essential developments.” He specifically mentioned several: in the LW category, “the development of the AN/TPS-10 when we already have in production four light-weight early warning radar equipments to perform the same task”; and in height-finding applications “the development of V-Beam equipment when we already have seven pieces of equipment to give us the height of an airplane, five of which are in good production.”21
Microwave types of radar had replaced most long-wave radars in laboratory development by mid-1943, but microwave radar production by American industry had not yet offset the long lead enjoyed by the older long-wave sets. The latter therefore continued to outnumber microwave sets in the field, especially on the ground. Thus it was that the Army Air Forces, although they had decided by mid-1943 that they would need no more SCR-270’s or 271’s, nonetheless continued to operate the older radars in large numbers. In fact, the AAF estimated that through the fiscal year of 1945 it would keep 113 SCR-270’s in operation and 61 SCR-271’s. As late as
Base of SCR-270 radar, showing azimuth scale, Vanua Levu, Fiji Islands
October 1943 the Navy asked for 50 SCR-270’s.22
By 1944 the oldest and most numerous of American radars, the ancestral SCR-268, was far down its decline. As of the middle of the year, 600 sets (issued for GL, an application for which this radar had never been intended but for which it was better than no radar) had been replaced by SCR-584’s. Even so, some 1,200 SCR-268’s remained in use for searchlight control, the function
for which the sets had originally been designed. In this role the 268 served very well to the war’s end, since its microwave successor, the AN/TPL-1, did not come into production in time to replace it in the field. The old 268’s, even in discard, still had value, for in mid-1945 atomic researchers would ask for them in large numbers for postwar research in atomic energy.23
The old long-wave radars yielded to the new microwave types as fast as the latter reached the field. Allied researchers generally ignored the medium-wave types, in the 500-megacycle range wherein the Germans had very early attained their greatest success and wherein too they later bogged down (the Signal Corps produced one set in the medium range, the excellent SCR-602 type 8, or the AN/TPS-3, used late in the war as an LW radar).24
The microwave SCR-584 replaced the 268 in GL applications. The MEW, or AN/CPS-1, likewise began to replace the 270 and 271 in EW, but never reached the field in anything like enough sets to put the older types of long-wave radar out of business before the war’s end. This was especially true of the Pacific where priority for microwave radar equipment rated below that of the European theater and therefore was later arriving there. “The radar war in the Pacific was, as far as ground equipment went [except for SCR-584’s], largely fought with long wave sets.” The authority who made this statement also noted a greater lag of radar applications in the immense Pacific areas. This he attributed primarily to the difficult supply problems there, as well as to the fact that radar methods and equipment used effectively in Europe were impossible or impracticable in the Pacific. Finally he noted a lack of centralized control over Army operations in the Pacific as a whole.25
Foremost among new microwave ground radars was the microwave early warning pioneered by the Radiation Laboratory. Designed as the AN/CPS-1 to replace the old long-wave SCR’s-270, 271, 527, and 588, this radar took a new departure with its novel antenna array, a long horizontal half cylinder.26 The set at first impressed the Signal Corps variously. Some representatives viewed it apathetically because, for one thing, the radar in its prototype form could give only azimuth and range of a target and
Microwave early warning antenna, Okinawa
not its altitude.27 Others reacted with enthusiasm. Colonel Metcalf, chief of the Electronics Branch in OCSigO, asked the Air Forces to take action to determine the characteristics the AAF desired for the MEW. He urged conferences wherein representatives from the Office of Scientific Research and Development, the Air Forces, and the Signal Corps could coordinate MEW design, “so that procurement may be undertaken at the earliest possible date.” He foresaw that MEW “may prove to be a definite improvement over our present equipment (SCR-270, 271, and 588); particularly, in its probable freedom from enemy jamming and in its improved performance in mountainous terrain.”28
The Air Forces rushed the military characteristics. The Radiation Laboratory rushed a preproduction set for the Signal Corps to test at the AAF School of Applied Tactics, and General Colton
established a project for the AN/CPS-1 at the Camp Evans Signal Laboratory to supervise the activity.29 Although it would be summer of 1943 before even the preproduction set was ready for testing, the Air Forces, overly hopeful, asked for twenty-five sets to be produced that year and another seventy-five in 1944. The AN/CPS-1 was a super giant in the realm of giant radio sets, which radars were. Weighing over sixty tons and as complicated as it was ponderous, it could not be hurried.
Men and papers scurried among the several agencies involved in its development, which was beset by changes of plan, changes of design, and changes of military characteristics.30 Amid prolonged difficulties over the manufacture of the production set, the first laboratory-built MEW under test at AAFSAT in Florida proved itself to be far more than a mere long-range search radar.31 “Preliminary experiments ...” Colonel Rives stated in November 1943, “indicate that this set can be used for controlling friendly aircraft on bombing, photograph, and reconnaissance missions, as well as fighters on intercept missions.” Prophetic words. More and larger oscilloscopes were needed to present all the information which the long concave antenna gleaned, as it rotated, from the skies.32 Five laboratory-built models known simply as MEW’s went overseas in 1944, while production of the CPS-1 got under way at home, just as its successor, the prototype AN/CPS-6, began undergoing its tests at the AAF School of Applied Tactics. In this last set, microwave techniques would finally meet Air Forces’ long-standing demand for a GCI radar that could determine with accuracy target height as well as range and azimuth.33
Just as the MEW provided the best solution of radar problems in EW and GCI, so the SCR-584 proved to be the answer to the antiaircraft artilleryman’s prayer.34 Army’s SCR-584 became popular with the AAF, too, when it discovered that the set could alleviate problems
of air interception. The AAA batteries, under air control, could be so accurately pointed by the microwave GL radars that they could shoot down enemy planes at night, relieving to some extent the demand for airborne interception radars in night fighter airplanes. Early in 1943 an Air Forces officer had informed Brig. Gen. Gordon P. Saville, charged with air defense, that the new 10-centimeter radars, employed with 90-mm. gun batteries, would “materially reduce hostile night bombardment.” He therefore wished to secure the sets to supply to all 90-mm. gun batteries in the North African, South Pacific, and Southwest Pacific theaters, in order to “lessen the horrible scream for night fighters.”35 By mid-1943 the Signal Corps had completed the final design of the SCR-584 and was reducing the tremendous problems encountered in its production.36 At the year’s end microwave gun laying radar was ready to replace the long-wave SCR-268. At last the medium-wave German Wuerzburg, the best GL radar up to this time, would be outclassed.
A new factor that hastened the demise of the SCR-268 and promoted the SCR-584 was enemy RCM. After the raid on Hamburg in mid-1943, the Germans began retaliating very effectively against Allied long-wave radars. In November the Signal Corps informed the Air Forces that no amount of redesign could greatly improve the SCR-268 against jamming. All long-wave sets were susceptible “to the present form of enemy Window,” General Ingles wrote, urging that “considerable effort should be directed toward the replacement of SCR-268 by SCR-584 for gun laying applications.”37
Even as General Ingles wrote, the effort was beginning, with tryouts first in England and then in Italy. In England, the microwave SCR-584 immediately outperformed the British (Canadian-built) long-wave GL-3. Early in November came a report that the 584, feeding target data to a British predictor (or director, in U.S. terminology) that controlled the guns of an AA battery, had seen action against enemy raiders and had proved “very effective.” Another report, comparing the 584 with the GL-3, stated that the SCR-584 located 80 targets where the Canadian set detected only 20. This particular 584, with an American crew, had been operating for three weeks, the report added, “without breakdown of any kind,” under the British AA command on the Isle of Sheppey in the Thames River estuary.38
Generally used with the American computer M-9, the SCR-584 proved to be the best ground radar airplane killer of the war.39
In Italy the SCR-584 met the test of combat at Anzio, where older longwave British and American radars were being reduced to ineffectiveness by German jamming. On 24 February 1944 the first 584’s, together with an SCR-545, arrived on an LST from Naples.40 One of the 584’s was at once put to work supplementing a British 10-centimeter GCI radar, the Ames (Air Ministry experimental set) 14, which suffered from land echoes at ranges within twenty miles. The SCR-584, on the other hand, “gave automatic tracking on low flying aircraft out to 27 miles with an early warning range of 56 miles. Height accuracy up to 18 miles (away) was 200 feet and beyond this range the height readings were accurate within 1,000 feet. The two sets operating together gave an exceedingly effective GCI control, the SCR-584 taking care of interceptions from 0-20 miles and the British set from 20-60 miles.”41
“When I first arrived at the Beachhead,” wrote Maj. Harris T. Richards, a Signal Corps radar officer from the Allied Force Headquarters, “the enemy was doing formation bombing of the Anzio-Nettuno Port Area. The SCR-268 was so effectively jammed by ‘Window’ and land jamming stations that the enemy had no worries from AA fire.” But the 584’s changed all that (by April the 68th and 216th AAA Battalions were completely equipped with 584’s and the 108th AAA Battalion with 545’s). “After three SCR-584’s were put in action,” Richards reported, “and five E/A [enemy airplanes] out of a formation of twelve were shot down, the enemy did no more formation flying over the area.”42
Everyone wanted SCR-584’s. The commanding general of the AAF in the North African theater complained that his 268’s were being jammed and could not satisfactorily direct either searchlights or night fighter operations. He asked if better SLC radars would be furnished soon, or if 584’s could be had. He explained that microwave radars,
such as the SCR-584, performed very well despite enemy jamming. He soon learned, however, that he would have to continue using 268’s for searchlight control since the first production of a microwave SLC set, AN/TPL-1, was at least a year in the future. But the 584’s would fast become available for gun laying, chiefly for antiaircraft artillery batteries. Coast Artillery wanted the sets for sea targets, to direct their 155-mm. mobile guns, while awaiting production of new microwave CD (coast defense) radars, the AN/TPG-1 and the AN/MPG-1. For example, in the Pacific the Coast Artillery immediately demanded 28 SCR-584’s and 56 qualified Signal Corps maintenance men, specifying 7 sets for Oahu alone and the rest for various advance bases.43
Strong demands also came from the Army Air Forces. Here was a radar that had been developed with the simple thought that it would serve as a gun layer for ground force use with AA guns. It was toward this end that the Signal Corps had taken over the prototype, XT-1, from the Radiation Laboratory and had militarized it, produced it, and was now distributing it for use by the Army Ground Forces and by AAA battalions.44 But now, too, the set suddenly appeared to have special air applications, for example, for the control of aircraft in flight, a GCI radar, and so very much the Air Forces concern. In February 1944, General Ingles informed the Army Ground Forces that “the Army Air Forces will soon test a Radio Set SCR-584 to determine its suitability for use as an advanced stage GCI set,” and he asked the Ground Forces to “make available to the Army Air Forces an experienced SCR-584 operating crew. ... The Signal Corps,” he added, “will provide maintenance personnel.”45 In mid-April, commanders in the European Theater of Operations requested twenty SCR-584’s modified for use as emergency GCI radars. True, their relatively short range, designed for gun laying only, was a defect in GCI. The range could, however, be increased, and was.46
Within a month after the GCI request, AAF officers were contemplating using the set for another function, for directing fighter-bombers to ground targets. This radar could “see” both the planes above and targets on the ground below, miles away. When the bombers, coached by a controller using SCR-584 information, arrived over the target, their pilots could be told by
radiotelephone the exact instant at which to drop their bombs.47
This surprising use of a ground radar as a bombing aid would depend upon very accurate maps used in combination with precise plotting equipment at the radar site. Then the radar operator could track a friendly bomber in flight with such accuracy that he could precisely locate the plane in relation to the terrain below at any instant.48
Air Forces interest in the SCR-584 did not stop with this amazingly refined application of the radar. The AAF next wanted to employ the set for meteorological uses as well—to locate and track storm areas up to the maximum range, about forty-five miles. After allocating thirty-five sets for this special use, the AAF discovered that the British branch of the Radiation Laboratory had modified some of the 584’s in the European Theater of Operations, increasing their range. Accordingly, the Air Forces asked the Signal Corps to provide kits to increase similarly the range of the thirty-five meteorological 584’s, enabling them to detect storm clouds out to seventy-five miles.49
The SCR-584 thus became quite a versatile set. Conceived, developed, produced, and originally distributed solely as a gun layer, it became every kind of radar, from a basic GL to an SLC and CD, a GCI, a ground bomber controller and guide, and a meteorological set for Rawin and storm detection. Finally, when it was found possible to step up its range to 96,000 yards, the SCR-584 became a good medium-range warning radar as well. Such are the unpredictables that may arise in the research and development of military equipment.50
Equally unpredictable are the inclinations or disinclinations of men to employ the potentialities of such devices. The AAF generally tended to present an open mind to all possible uses. In general the AGF, swamped in
masses of men many of whom it was hard enough to train in the rudiments of warfare and simple equipment, was less perceptive. When radar specialists suggested in mid-1944 that the SCR-584 potentiality indicated possible uses by ground troops (to detect, for example, ground targets such as vehicular and tank traffic at night), certain ground force officers, headed by no less than General McNair, objected to such novel notions. These ideas, connoting more complex equipment, would complicate, they believed, the overwhelming training problem with which the Army was already confronted, the problem of how to teach the men to use with reasonable efficiency the equipment they already possessed.51
The SCR-584 Radar, VT Fuzes, and the Buzz Bomb
It was, of course, in its intended use as a gun layer that the SCR-584 stood unsurpassed, a fact abundantly attested from Anzio on. Its supremacy shone forth with high drama during June, July, and August 1944, during the defense against the invasion of England by pilotless buzz bombs. British intelligence had learned that such an attack would come. The situation seemed desperate. There had been a radar answer (CH) to the 1940 air raids by day; also a radar answer (GCI and AI) to subsequent air raids by night. But now the Germans were systematically and thoroughly flooding all the old British long-wave radars with jamming signals. For example, SLC radars were being so completely blinded that searchlight crews in England were falling back upon outmoded sound locators. Microwave gun layers, whose very short wave lengths and narrow beams of radiation rendered them much less susceptible to jamming, were now needed badly. Yet the British microwave GL radar program had not been pressed, in part because Professor Frederick L. Lindemann (Lord Cherwell), Churchill’s own scientific adviser, had taken a dim view of radar antiaircraft fire control. Confronted early in 1944 with the threat of the flying bomb, the British commander of the Antiaircraft Command, General Sir Frederick A. Pile, turned to the American SCR-584. “It seemed to us,” he wrote, “that the obvious answer to the robot target or the flying bomb (against which we were now being warned) was a robot defense, so I asked for an immediate supply of 134 of these amazing instruments. I wanted to get eventually at least 430 of them. ...” He added:
As usual it was the Prime Minister who made this possible. I think it was at a Night Air Defense meeting at the end of February ’44. ... Fortunately for me Churchill was determined to hear what I had to say: “I want the General to tell us what equipment he wants,” and so I did. The result was that the Prime Minister ordered the War Office to do everything they could to obtain the S.C.R. 584 and, indeed, everything that went with it.52
“Everything that went with it” involved first, RC-184, which was
Mark III IFF equipment, then maintenance and repair sets, and finally the complex electrical computer M-9. As General Pile had recommended, this was indeed a robot defense, all automatic (except that loading the guns was still done by hand) and superhumanly accurate, rendered still more so by the VT, or proximity fuzed, projectiles, which needed no human touch to set, but which exploded when the tiny radar (or doppler radio) built into the fuze sensed a target within a hundred feet. All this complex of American equipment was rushed to England along with artillerymen and technical experts from the Radiation Laboratory and the Signal Corps. One group, arriving on 10 February 1944, described its mission thus: “to prepare units as quickly as possible for using the SCR-584 radar, M-9 director, and 90-mm. guns for defense against a specific threat known as CROSSBOW, the projection of crewless, heavily loaded, jet-propelled planes from the coast of France towards the London and Bristol areas.” When the group had completed its mission by 1 May, it had readied nearly 100 90-mm. batteries complete with the 584.53
The Allies were therefore prepared in June, when the V-1 robots first began coming from over the Channel bearing their deadly cargoes. The robot weapons, meeting a nearly automatic defense, uncannily accurate, exploded in the sky or crashed in open fields. Antiaircraft artillery guns, aided by the SCR-584, the M-9 computer, and the proximityfuzed shells, brought down most of the buzz bombs. On one day, for example, 68 were shot down by antiaircraft artillery; 14 by Royal Air Force pursuit planes; 16, which early warning radars detected, failed to reach the coast; 2 collided with barrage balloons, and only 4 buzz bombs out of a total of 104 the Germans had launched that day reached London.54 All in all, the defeat of the buzz bomb was an extraordinary achievement of the new technological warfare. To the SCR-584 went the laurels. “Without this equipment,” General Pile categorically asserted, “it would have been impossible to defeat the flying bomb.”55
Successes and victories often hang on slender threads of effort and chance. In this instance they rested on the intertwining of certain research, production, and training efforts, combined with certain essential human relationships and confluence of events. General Pile recounts that he sent Maj. William M. Blair of his staff to Washington to ask for the 584’s, hardly expecting he could get them. “Although, on his arrival, there was very little hope that his mission would prove successful, a 35-minute meeting with General Marshall, U.S. Army Chief of Staff, put a very different complexion on things,” Pile wrote subsequently, “Largely due to the General’s influence an immediate allocation of 165 S.C.R.584’s, together with all their ancillary equipment, was made, and they were
shipped to England on the very next boat.”56
SCR-584 Modifications
By their very nature, research and development never stop. There is always room for improvement. So it was with the SCR-584. In mid-July 1944, a prominent British civilian physicist, J. D. Cockroft, wrote General Colton that he had been experiencing the buzz bomb attacks for several weeks. “We had to take some very active measures,” he said, “to improve the shooting of light and heavy AA. The SCR-584 combined with the BTL Predictor is showing very great promise.” But, he complained, when the 584 was employed against bombs flying especially low, it was “apt to lock onto ground clutter.” When that happened, the oscilloscope operator would lose the reflection from the target in the mass of reflections from objects on the ground. On the margin of his note, Cockroft penned additionally, “Narrow strobes (N2 gates) are therefore required.”57
Gate was an antijamming device, devised by the Radiation Laboratory late in 1943 and sponsored by the Signal Corps. Named simply N2, it had been developed as part of a program to render the set less susceptible to jamming. The N2 had other advantages. For one thing, it greatly increased the minute accuracy of the radar. It reduced the length of the pulses to a fraction of a microsecond and it reduced the time between the pulses, when the receiver listens for the echo. The effect was that it eliminated many echoes, thus reducing ground clutter, and increased the capacity of the radar to discriminate between a target and other objects. For tracking the small low-flying buzz bomb, N2 was an invaluable refinement. The Radiation Laboratory crash-built fifty N2 kits for the European theater. The Army Ground Forces asked Signal Corps to equip all SCR-584’s with N2 Gate “at the earliest practicable date.”58
The Signal Corps provided N2 kits to modify existing SCR-584’s under the designation MC-581. The kits were in demand everywhere. Hurach B. Abajian, a Radiation Laboratory engineer who had helped to develop the SCR-584 and who had been sent by the Army to solve 584 problems in the Pacific, wrote to Colonel Winter in midsummer 1944, “Since I put my only N2 Gate on a unit at APO 709, I’d like nothing better than to put one to work in Northern New Guinea. Can you please have one sent to me in Brisbane?” He added as a postscript, “I’ll take as many N2 Gates as you can send.”59
All these encomia and elaborations should not be taken to suggest that the progress of the SCR-584 in the U.S. Army was entirely free from trouble. There were the usual defects in the first factory productions: bad tubes, poor soldering, incorrect wiring. A number of complaints came from the Fifth Army in Italy, whither the first 584’s had gone early in 1944. Four sets put ashore at Hollandia in April 1944 soon broke down because of failure of the highvoltage modulator transformer T-214. Faulty workmanship in the factories received blame for breakdowns in electrical servomotors and in cable connectors. Errors in wiring explained units that could not possibly function and oscilloscope sweeps that rotated backwards. There was some complaint over the lack of spares. In general, however, the complaints were slight in proportion to the numbers and complexity of the sets, and spares were generally available—all of which contrasted favorably with the anguish of supply, maintenance, and spare parts bedeviling Signal Corps radar in 1942 and 1943.60
There was yet another problem—lack of trained SCR-584 operators. Too often field units did not know how to use the 584 when they got one. Major Richards, describing the 584 success at Anzio, was emphatic on one point, “operators and maintenance personnel must be thoroughly trained and know the equipment inside and out.”61 Yet competent operators were rarer than the proverbial hen’s teeth, as is generally the case when new equipment reaches the field, unless
special efforts have been made to repair the deficiency. For example, in the far Pacific SCR-584’s had arrived as early as March 1944, but not everyone there knew how to employ them properly, at least not in General MacArthur’s Southwest Pacific command. General Colton scurried to find someone whom he could send to advise and instruct. He wrote:
Radar Sets SCR-584 were received in the Southwest Pacific Area by 4 March 1944, but three secret radiograms received from that Headquarters and signed MacArthur indicate that they are not being used. The reason for this condition is because the operation of these sets is based upon radar techniques unknown in that theater and a man who is well trained on this set is needed. Mr. Abajian is such a man; however, he is not available, for he was sent to the European Theater of Operations in order to introduce the set there.62
When instruction books arrived in advance and when competent SCR-268 operators were able to study the 584, they could easily switch over to the new microwave radars, and they did so with zest, as did the radarmen of the 3rd Marine Defense Battalion in the South Pacific Area.63 But Army radar manuals, classified “secret,” frequently never reached the troops precisely because the books were stamped “secret.” Consequently, operators of the older long-wave radars often remained uninformed, if not apathetic.
So it appeared to Mr. Abajian when he was dispatched by the Signal Corps to the Pacific in July (after completing his ETO mission, setting up 584’s for CROSSBOW). By mid-1944 several scores of SCR-584’s had gone out to the South and Southwest Pacific. Of the units he visited Abajian found that “without exception every gun battalion is employing the SCR-584 almost exactly as it used the SCR-268. ... This inexcusable failure to use the SCR-584 and M-9 combination to the fullest of their capabilities,” Abajian wrote, “can be traced to the lack of instruction and information, to battalion and battery commanders, on the tactical use of the radar and on its characteristics.” He said further:
Every battalion visited so far had been overseas long before the SCR-584 was delivered to them. None of the commanding officers had ever seen it perform against an aircraft. All practice firing had been executed with cloth sleeves, the signal from which is so poor that automatic tracking is almost impossible. Witnessing such performance served only to create doubt among the officers. The situation can be summed up with a direct quotation of one battery commander: “Hell, I’ve never seen shooting with it. You send me a new piece of equipment I never even heard of until shortly before I got it. I’m not going to accept anyone’s word for it until I see it work.
Thus, for want of instruction, millions of dollars’ worth of superlative new radar lay unused in an active theater of war. Abajian had a missionary job to do—demonstrate, teach, and spread the gospel to the doubting Thomases. He checked over the sets and asked each battalion to send an officer and two men to attend a course on the 584. He often got people who were not radarmen at all, these being needed to keep the 268’s in operation. One battalion sent its S-2 officer. During his work with the 66th AAA Brigade, Abajian spent a week with each gun battalion, adusting their radars and instructing the operators. The commanding
general of that unit, Brig. Gen. Charles A. French, was appreciative, saying that Abajian’s work “has been of immense value to this brigade.”64
Airborne Microwave Radars
Microwave radars had been mothered by the necessity for smaller sets to be used in aircraft. By the mid-point of the war airborne applications were multiplying amazingly. The Signal Corps was “more or less in charge,” as certain officers aptly summarized its role.65 The Radiation Laboratory and its civilian scientists under the OSRD carried the burden of research and development. The Signal Corps, through its Aircraft Radio Laboratory, helped adapt the initial laboratory creation to a militarily useful form. Then the Signal Corps shouldered its heaviest task, getting the manufacture of the equipment under way and procuring the sets. By that time, in mid-1943, airborne microwave techniques, microwave circuitry, tubes, and testing equipment were well established, after the success of the first microwave AI’s, such as SCR-520 and 720, against enemy night aircraft and after the victory of the microwave ASV’s, SCR-517 and 717, and Navy’s ASG (airborne search radar) over German submarines.66
As the Germans increasingly jammed Allied radar, microwave airborne sets acquired further value. In August 1943 the Royal Air Force, for example, asked for SCR-720’s; Air Chief Marshal Sir Charles Portal explained that their microwave length rendered them far less vulnerable to Window Countermeasures, which were reducing British long-wave AI-IV to uselessness. Fortunately, the production rate of the 720 enabled General Arnold to grant the request. Signal Corps procurement of the microwave ASV SCR-717, however, had encountered difficulties. The manufacturer, Western Electric, could not meet schedules and the Signal Corps had to turn to the Navy, ordering 2,450 ASG’s.67
Along with the ASV microwave sets, the laboratories developed a bombing aid (it had been initiated in the Signal Corps in August 1942, for use with the SCR-517) that permitted accurate bombing from low altitudes. Known popularly as LAB (low altitude bombing) , technically as AN/APQ-5, it helped to sink many ships in the Pacific. LAB had been developed as a stopgap technique until good BTO radars could
be perfected. Rather than sending out the equipment with any expectation that uninitiated commanders in the theaters could readily put it into effective use, Dr. Bowles and the AAF set up a squadron of planes and pilots complete with radar operators and maintenance men, trained them as a unit in the States, and then sent the outfit to the Pacific to operate under the local combat commander, who welcomed them and was soon convinced of the value of their special skills. This was the way, Bowles believed, to introduce effectively specialized techniques and to win acceptance for them by the theater commander.68
Other notable 10-centimeter S-band radar aids included the ARO’s (air range only), which were airborne range finders. The Signal Corps and Western Electric, beginning as early as November 1940, had worked on such a set, the SCR-523, but the models were too heavy. Next, the Radiation Laboratory at MIT, making use of a new microwave oscillator tube by General Electric—the lighthouse tube—developed an acceptable ARO. First named the SCR-726, then the AN/APG-5, it came into production by the Galvin Corporation in 1944.69 Another ARO was Falcon, or AN/APG-13, employed with 75-mm. cannon, which were specially mounted in B-25’s for firing on Japanese shipping in Chinese waters.70
ARO quickly led to AGL (airborne gun layers), which would lock on a target and direct the turret guns of a bomber, doing in the air what an SCR-584 did on the ground. The Aircraft Radio Laboratory worked upon a variety of AGL’s: SCR-580 and 702, becoming AN/APG-1 and 2, which were 10-centimeter Sband sets; and AN/APG-3, a 3-centimeter or X-band radar.71 Used only at the very end of the war in B-29’s these radar gun sights were forerunners of sets that would prove effective against jet fighters of the Korean War. AN/APG -15 grew out of SCR-580, dating back to 1941 in ARL efforts, for use in experimental B-32’s.72
Among the many radar projects at the Aircraft Radio Laboratory and at the Radiation Laboratory, none received higher priority or more lavish attention than radar for bombing through overcast,
Drawing of an an AGL type radar installed in the tail gun turret of a large bomber
that elusive objective the Air Forces had been pursuing since the late 1930’s. Precision navigational systems had pointed to one solution, but a limited one. ASV radar had indicated a better method. Already ASV had proved so effective against sea targets that it had tipped the scales in submarine warfare. But the first ASV sets had not been quite good enough to “see” land targets well. Bombing German land targets was now the number one problem, especially in the German interior beyond the limited reach of Oboe, Gee, and Shoran navigational systems of blind bombing (the first two were British; Shoran was an ARL development, originally SCR-297) . These systems proved helpful in air attacks through 1943.73
For example, Oboe had enabled the first large-scale (1,000 planes) blind bombing of an area target, Cologne. Oboe was more than just helpful; it was absolutely necessary since clouds cover much of Europe much of the time, especially in winter. But the range of the
system ran to only about 200 or 250 miles, far short of Berlin and industrial centers in east and south Germany. What was wanted was a radar that could “see” the ground well enough to drop bombs accurately anywhere, anytime. The demand grew. When, in December 1943, General Colton ordered stoppage of much research and instructed the laboratories to shift their engineers to preparations that would promote the invasion effort, he specifically exempted the BTO program at the Aircraft Radio Laboratory.74
He had to exempt it. Throughout the last half of 1943, the Air Forces had pressed hard for an American 3-centimeter, or X-band, BTO. The AAF wanted this set, called H2X or Mickey, as an improvement on the British 10-centimeter, S-band, blind bombing aid that was sometimes called H2S, sometimes Home Sweet Home, or even Stinky (since H2S is the symbol for hydrogen sulphide, or rotten-egg gas, known to every high school chemistry student). Upon the Signal Corps rested the urgent demand for Mickey, AN/APQ-13. In August 1943, General Arnold had requested that thirty sets be delivered before the end of the year.75 He did not get them until January 1944, when the Signal Corps extracted mass production of an H2X from Philco. Even the Philco product was not the desired AN/APQ-13 but a less acceptable variant, the AN/APS-15. Already in the late summer and autumn of 1943 the Radiation Laboratory had put together from components of the Navy ASG a number of APS-15’s. These sets the civilian laboratory had mounted in B-17’s of the 612th Bombardment Squadron of the 482nd Heavy Bomber Group.76
The B-17’s, so equipped, served as pathfinders, flying ahead of the main bomber force. Their radar operators, viewing the ground dimly in their oscilloscopes through any amount of cloud and overcast, located their targets and dropped smoke markers, over which the rest of the bomber fleet jettisoned their deadly cargoes, accurately enough for area bombing. Beginning in November, with Wilhelmshaven and Bremen as the victims, the Eighth Air Force bombers attacked again and again, “guided entirely by AN/APS-15 ‘X’ band radar sets installed in leader aircraft.”77 They hit their targets with considerable accuracy, sufficient to bring inescapable destruction, despite cloud and night, upon German cities and large industries. German leaders and scientists knew it when they reconstructed a British H2S radar in August 1943. With horror they recognized that the Allies had mastered microwave techniques they had thought impractical. With microwave radars the Allies had defeated the U-boats, the Nazis now realized, and they would next
pound the fatherland itself—every target in it worth a fleet of bombers. And what the British 10-centimeter H2S could do, the American 3-centimeter H2X sets could do better, the first of which the Germans recognized and recovered from an American bomber shot down early in 1944 in Holland.78 Lt. Gen. Carl Spaatz vigorously sought more and more Pathfinders—“the most critical need of the Strategic Air Forces,” he wrote General Arnold in January 1944, “is for more Pathfinder aircraft. A few H2X airplanes now will profit our cause more than six hundred in six months.” He continued:
“Results of the past two months’ extensive use of Pathfinder (H2X) aircraft in the Eighth Air Force has shown that the equipment offers enormous possibilities for further intensification of the bombing offensive against Germany. Because of the prevalent cloud cover over the targets, it has not been possible to photograph the damage from each mission. While complete assessment of the accuracy of H2X bombing is therefore impossible, we do know that large concentrations of bombs hit precisely in the aiming point at Kiel, Wilhelmshaven and Bremen—the only targets where photographic interpretation was possible after a large H2X operation. These strikes indicate that the potential accuracy of H2X bombing justified the highest priority in providing this equipment on the scale recommended herein. The original twelve B-17’s with experimental H2X sets built by hand in the Radiation Laboratory have led seventeen out of the twenty missions by the Eighth Air Force in the last two months. Cloud has prevented visual operations nine-tenths of the time.79
By the time production in the thousands got under way, however, the need for both the standard H2X, AN/APQ-13 (built by Western Electric), and the stopgap Philco AN/APS—15 was lessening in the ETO. All through 1944 the bombers devastated their targets, railroad yards, dock areas, concentrations of factories, but “area bombing,” a Signal Corps report in 1945 read, “was becoming less remunerative as large areas were destroyed and only isolated targets remained.” Area targets did remain in Japan, and the AN/APQ-13 mounted in B-29 bombers proved their worth there during the last months of the war.80
Already the nemesis of the small isolated target was at hand—a remarkable 3-centimeter BTO called the Eagle (AN/APQ-7), which an Air Forces officer remarked in April 1944 was “the first blind bombing equipment which shows promise of meeting the M/C’s.” Even so, the Signal Corps had had occasion to complain that the lack of a suitable airplane to try out the new model was delaying the Eagle program (an old, familiar complaint at the Aircraft Radio Laboratory). The Air Forces had indeed assigned a B-24 for
this purpose, but it had to be overhauled before it could fly. Moreover, the Air Forces had delayed contracting for a number of strictly Air Forces items that the Eagle’s antenna would require—a special wing with struts and deicers. General Arnold summarily removed these difficulties when he ordered the Air Service Command to meet all Signal Corp requests touching Eagle, since “the program has the highest priority.”81
Beginning with a flight test of the laboratory equipment as early as September 1943 over the Connecticut River valley, Eagle marked the peak of the long BTO effort. The set was remarkable in many ways—for instance, in its antenna. Eagle carried aloft the long narrow array (the Alvarez leaky wave guide, developed by the Radiation Laboratory) that had made the MEW a revolution among the revolutions that all military radars were. Entirely unlike the parabaloid bowl antenna that had characterized previous microwave airborne radars, this linear array of several hundred tiny dipoles totaling about sixteen feet in length had to be mounted in the leading edge of a wing, a special wing fastened beneath the bomber fuselage. And instead of yielding a round 360-degree PPI (planned position indicator) oscilloscope presentation, Eagle spread upon its scope a fanlike view of the radar scene below. There was no troublesome “eye” at the center, as in a round PPI picture. The resolution was better than anything attained hitherto—that is, the picture was clearer and showed more detail. Even in the first test over the Connecticut River the set had showed all the towns, rivers, and streams, the bridges over the rivers, and also the hills and their shapes, which could be determined by the radar shadows they cast. Eagle got into the war just in time to enable a few devastatingly destructive strikes against Japan.82
There were still other airborne radars—for example, tail warning (TW) sets. Developed by the Aircraft Radio Laboratory as AN/APS-13 for fighters and as AN/APS-16 for bombers, these radars were small, designed to scan a mile or so of space behind an airplane. Upon detecting any object in the area (most likely an enemy fighter closing in for a kill), the set automatically flashed a warning light in the cockpit.83
In addition a whole family of navigational radars or beacons sprang up, beginning with an airborne IFF interrogator-responsor, the SCR-729. IFF had originally been necessary for ground radar operators to challenge an
aircraft and receive an identifying response. When aircraft themselves began carrying such radars as the ASV (SCR-521), it became necessary for the radar operators aloft to challenge ships or ground targets below and receive an identifying signal in reply, else the pilots assumed them hostile and attacked. The Aircraft Radio Laboratory, the Radiation Laboratory, and Philco developed and produced the SCR-729, an airborne interrogator-responsor, in 1943. It could challenge and receive responses from Mark III IFF sets in other airplanes, on ships, and at land installations. It acquired also another very valuable use: it could, for purposes of navigation, challenge, identify, and locate in azimuth and range special ground radar beacons. One such ground beacon was developed as AN/CPN-7, or BABS (blind approach beacon system). Another was a beacon developed for rescue at sea, the AN/CPT-2; it emitted signals that an aircraft equipped with an SCR-729 could pick up and on which it could home. The two beacons were developed by the Aircraft Radio Laboratory in 1943 and 1944, respectively, following British precedents.84
A group of navigational radars that became vitally important in parachute operations was the Rebecca-Eureka combination, British named for British prototypes. The Eureka was a portable ground beacon, which a soldier set up at a point where paratroopers were to land. Rebecca sets, aboard troop carrier aircraft, interrogated the ground set, whose responses enabled the pilots to fly directly over the drop area. The Aircraft Radio Laboratory developed Rebecca, AN/APN-2, which was similar to the SCR-729 but which operated on somewhat higher frequencies. As for the Eureka type, the Aircraft Radio Laboratory converted the Mark III IFF radar SCR-695 into AN/PPN-1 and 3. Subsequent Eureka development, however, AN/PPN-1 and 2, was transferred to the Camp Evans Signal Laboratory in New Jersey, since Eureka operated on the ground and so was a ground radar.85 The Air Forces in mid-1943 requested that the Signal Corps procure 1,366 sets of AN/PPN-1 in 1943 and a like number of PPN-2’s in 1944. Though the goal was not reached, nearly a thousand sets were delivered before mid-1944, just in time for D-day operations in Normandy.86
According to Colonel Metcalf, chief of the Electronics Division of the Office of the Chief Signal Officer, who was in
EUREKA ground beacon guiding planes home
ETO at the time of the invasion, these beacons accomplished “the most outstanding use of airborne electronic devices in combat operations.” He was speaking of the drop of 20,000 paratroopers by the IX Troop Carrier Command on 6 June 1944. Colonel Metcalf reported most favorably also on the BTO radar, AN/APS-15, of airborne gun layers, and of other aircraft radars that the British and Americans had crash-built. He had high words of praise for the hundred or so scientific and technical experts of BBRL. To these men and their counterparts in the Telecommunications Research Establishment—Britain’s equivalent of RL—he attributed the radar successes. “It was the uniform opinion,” he reported,” of all Air Force and Signal Corps officers consulted that the successful operation of this equipment would have been impossible without this group of civilian specialists.”87
Throat mike worn by a tank crewman, left, and lip mike, right. Both could be used with radio or telephone
Radios
During the first years of the war Signal Corps had, of course, been under heavy pressure to develop and supply ground and vehicular radios for the Armored Force and for the Infantry.88 By mid-1943 Army Ground Forces needs in this category were well in hand, thanks to full production of radios such as the “handie-talkie” SCR-536, the walkie-talkie SCR-300, the FM sets of the 500 and 600 series, and the SCR-299. Early in 1944 Colonel Williams, signal officer of the First Army in Europe, wrote enthusiastically to General Colton, saying “Armored Force sets SCR-508, 528, 538, and SCR-509 and 510 have become the backbone of communication within the armored division.” The same was true of the 600 series (SCR-608, 628, 609, and 610) in artillery communications whenever wire was not used and to supplement it when wire lines were laid. The 600 series, Williams also noted, had come into universal use by naval fire-control parties, naval beach communicators, amphibious engineers, and assault infantry during amphibious landings. These were short-range radios whose special virtue Williams ascribed to “the inherent advantages of FM in overcoming static and ignition interference and in giving a clear voice signal of
SCR-193 receiving and transmitting radio, mounted in a jeep
sufficient quality and volume to be heard over the noise of tank operation.”89
The long-range SCR-299 and 399 had proved so dependable that they had become the standard for distant communications among the Allied nations. The medium-range vehicular SCR-193, long described as the work horse among infantry radios, Colonel Williams called the Springfield rifle of the Signal Corps radios, outmoded but reliable. He expected that the new SCR-506 would prove a superior set, but using troops, when they got the 506, concluded otherwise. “The comments we have received from units equipped with the SCR-506, “ General Ingles wrote in April 1944, “indicate that it is not nearly as well liked as the SCR-193 it is replacing.”90
Combat troops, who had the best reasons to know, were exceedingly grateful for the advantages short-range Signal Corps radios of the FM types gave them. “One of the main reasons the American Army moved so fast against the Germans was that it had over-all information supplied by fast communications. In combat teams, that meant radio, and that radio meant FM.” These were the words of an infantry battalion radio operator, Technician Zens. He explained:
One night, up in the Siegfried Line, when we needed more equipment than we had [FM radios], we got out an AM set. The loudspeaker crackled and roared with static. Twenty different stations came in at once with a noise like a platoon of tanks. I think we heard everybody in Europe on that AM receiver. I mean at the same time ... English, French, Russian, German, ... At least, we heard everybody except the station we were trying to reach.
The FM radios gave clear static-free communications. Zens illustrated with several detailed and graphic descriptions of close combat in which the FM sets in the hands of infantry company and battalion communicators and in tanks and artillery units brought the Americans success. “FM saved lives and won battles,” he concluded, “because it speeded our communications and enabled us to move more quickly than the Germans, who had to depend on AM.”91
Ground Radio Types for the AAF
All ground radio needs had not been so happily met, and at the turn of 1943-44 the loudest demands for ground sets came from the Army Air Forces. They even wanted, surprisingly since they had once resisted them, FM radio sets.92 They had discovered that their requirements in ground equipment were growing—both for AM and for FM types in both the HF and the VHF ranges. They needed them in AWS nets and in fighter control (GCI) systems. They needed VHF sets for point-to-point use in their tactical air forces. Available frequencies in the already congested high frequency bands were next to nil, forcing the airmen to use VHF, although VHF immediately hit a range ceiling, the short distance of travel within line-of-sight. The Air Forces pressed the Signal Corps for any and every suitable radio: Collins transmitters, Hallicrafter receivers, Motorola (Galvin) sets (FMTR-30 DW and 50 BW), FM sets built by Fred Link (types 1498 and 1505), marine service radio sets, forestry sets, and a set called the Jefferson-Travis, JT-350.93
All this was extracurricular equipment so to speak, over and above the old SCR-188 and 197 the Signal Corps had standardized for the Air Forces long before; over and above, also, the numerous VHF transmitters and receivers that comprised the SCS-2 and 3 VHF fighter control systems. In September 1943 General McClelland, air communications officer, informed the Signal Corps that he had an immediate requirement for a set such as the Linktype 1498, complaining that the SCR-624 (a recently developed VHF set for ground use) was not powerful enough, could not handle several channels simultaneously, and could not be transported by air. Colonel Rives, General
McClelland’s deputy, informed General Ingles in December 1944 that the AAF was using the Link 1498 set as a stopgap and hoped to use the AN/TRC-1 similarly as soon as the AAF could get it. The AAF was also already using the Link-type 1505.94
In a desperate effort to get suitable ground sets (one officer characterized the ground radio situation in late 1943 as “extremely acute”),95 the Air Forces seemed to have looked into available commercial radios quite on its own and in so doing it left the proper radio supplier for all the Army, the Signal Corps, in a considerable quandary. For example, one such commercial radio that the Air Forces sought on the Army Supply Program, 1 August 1943, was the Jefferson-Travis transmitter receiver. AAF wanted 500 sets in 1943, 600 in 1944. General Colton, head of the Engineering and Technical Service of the Signal Corps, asked if the Air Forces wanted this set as an “adopted type.” AAF answered that it was wanted as “limited procurement type,” and explained:
Subject set was originally procured to fill an immediate requirement of a compact 50-75 watt HF radio set for mobile mounting in trucks to be used for radar reporting nets and for links in VHF systems where FM communication was not feasible. In this use it was intended to supplement SCR-188 Radio Set whose availability for this service was limited. Military characteristics closely approach those for SCR-188 with the exception that JT-350-A is designed to operate from 12, 24, 32, and 110V AC and for this reason is expected to be more flexible in operation.96
The Air Forces had evidently acted independently, somewhat disregarding the Army’s established procedure. The Signal Corps had not been informed of just what the Air Forces wanted in the way of ground radio, nor in fact does it appear that the airmen themselves yet knew. The Signal Corps could not, General Colton made it clear, readily develop or provide what the Air Forces seemed to want until the airmen made up their minds as to just what they did in fact desire. “In order that the Signal Corps may adequately comprehend the communications requirement of the Army Air Forces, and develop equipment suitable for meeting requirements,” General Colton wrote in August 1943, “it is essential that a knowledge of the proposed tactical use and desired performance characteristics be obtained.” Colton appreciated that combat experience had influenced the requirements and it followed, he added,
“that the Signal Corps personnel, whose responsibility it is to make such adaptations [as combat experience proved to be needed] must be fully informed of changes in requirements arising from such experience.” He suggested a conference before the conclusion of tests that the laboratories were running on the Jefferson-Travis set and on a Signal Corps set, the SCR-237. He mentioned, too, an innovation that the laboratories had recently completed in order to meet the Air Forces’ needs for an air-ground liaison radio, the AN/VRC-1. He called it an HF/VHF set, because it combined the old but very reliable HF SCR-193 with the VHF 12-volt version of the airborne command radio SCR-522, “but the intended use of this set in relation to Radio Set SCR-188-A and the Jefferson-Travis JT-350,” he pointed out, “is not known.”97
Radio Relay, From FM to Pulse Modulation
Out of the confusion attending Air Forces’ acute need for ground radio developed a growing demand by the airmen for the radio relay concept. AN/TRC-1 equipment was coming into wide Army employment in every theater of the war, and in June 1944 General McClelland indicated that the AAF also intended to make extensive use of radio relay in ground nets. McClelland wrote:
The requirements of the Army Air Forces for point to point VHF equipment are increasing in all theaters. ... Army Air Forces are issuing AN/TRC-1 sets to Fighter Control Squadrons for links within VHF systems and to Fighter Squadrons for inter-airdrome and squadron-to-group communications. In addition, AN/TRC-3 and AN/TRC-4 sets will be issued in many areas for multi-channel communications down to groups.98
Radio relay or antrac (often called VHF also, not to be confused with airborne VHF command radios such as the SCR-522) could well provide point-to-point communications for the AAF, as well as for AGF needs. Above all, in an era when ever more communications were wanted, it provided four voice channels and could be made to
provide many more, whether voice, teletype, or facsimile. It was compact and readily transported.99 From the first field improvisation (Motorola police radios in North Africa in early 1943) and from the first use in combat theaters a year later of production models of AN/TRC-1, 3, and 4, radio relay brilliantly proved its marked virtues.100
The radio relay concept, involving a revolutionary new kind of military communications facility, had taken form in the minds of officers and engineers in the Camp Coles Signal Laboratory before the concept was put to its first test in the field during the Tunisia Campaign in 1943. The concept had been developed on an “under the bench” basis at the laboratory since there was no specific authorization for such a project. When the value of the concept became recognized and demands for its implementation began to come from the field, the Signal Corps had equipment ready.101
The first order, for a small number of development sets of AN/TRC-1, had been placed by the Camp Coles Signal Laboratory with the Link Radio Corporation in New York City at the end of 1942. As of June 1943, the Air Forces requirement in the Army Supply Program stood at 1,116 sets to be delivered in FY 1943, at 1,632 sets in 1944. By August 1943, the need had so intensified that the 1944 requirement was increased to 4,372.102 Very few sets were actually delivered in 1943, however.
While the Camp Coles Signal Laboratory and the Link Radio Corporation developed the AN/TRC-1, the Air Forces asked that 300 sets be delivered before the end of the calendar year (it expected six service test sets in September 1943), and it asked further that 150 of the new walkie-talkies, SCR-300, be modified for their ground radio needs. General Ingles at once replied that current production of the SCR-300’s could not meet urgent ground force requirements. He added, “The delivery of 300 additional radio sets AN/TRC-1 during the current year will be even more difficult.”103
Difficult was right, not least because no one agreed on just what the set
should be. In fact, the set had been developed in the early and midyears of the war without benefit of military characteristics, those essential requirements in normal Army development and procurement matters. Willard R. Clark, who had worked on the radio relay project at Camp Coles (along with other radio enthusiasts such as Maj. James D. O’Connell, Major Marks, Capt. Francis F. Uhrhane, Capt. K. S. Jackson, and Lt. Oliver D. Perkins),104 later wrote that the Chief Signal Officer had authorized the project under his authority to provide communications of the most advanced type, without military characteristics. “The TRC-1 development was started as a laboratory investigation,” Clark explained, “in anticipation of future military needs.” Thus, the AN/TRC-1 was launched without the usual preparations. It had been promoted as a quickie, for needs that were likely to be immediate. A longer term research project was also under way at the same time in the Coles Laboratory for microwave radio relay, following the pattern of British pulse equipment. It would in 1945 yield the AN/TRC-6 and related radios, too late for much use in World War II. The TRC-1 sets, on the other hand, paid large dividends in the 1944 fighting.105
In April 1943 the Coles Signal Laboratory received delivery from the Link Corporation of eight models of AN/TRC-1. Modifying them as TRC-1, 3, and 4, the engineers and officers ran tests through the spring in the New Jersey countryside. They called the assembly a “100-mile radio relay system.” The military characteristics followed, in a cart-before-the-horse reversal of usual Army procedures. The first military characteristics, adopted in July 1943, were of “limited procurement type.” In September other tests of TRC-1 equipment were made over water along the coast of Maine, particularly atop Mt. Cadillac near Bar Harbor and on Cape Elizabeth near Portland, to duplicate conditions of communicating across the English Channel. The tests were successful and the system standardized.106
The Army Air Forces, which first sought quantity delivery of this equipment, kept making changes. Six service test sets built to its specifications were scheduled for delivery at the summer’s end but were not ready by November. Then, when representatives of the Air Forces Board and the Tactical Air Force, lacking the service test sets, went to the Link radio factory to check up, they asked that immediate steps be taken to incorporate additions and substitutions in the 2,740 sets under procurement. The AAF wanted a
different antenna, higher antenna masts, and remote control equipment.107
Meanwhile the Signal Corps took measures to expedite production. The Signal Corps labor officer in New York City deferred the induction of twelve of Link’s key men and got emergency furloughs for three men who had already been inducted so that they could return to their jobs as supervisors in Link’s metal shop and electrical assembly line. The Monmouth Procurement District had assigned two men to serve as coordinators at the Link plant, working full time there, expediting components. The New York office of ANEPA assigned one full-time expeditor to the Link plant and designated six people in the ANEPA office itself to give assistance on requests originating in the Link factory. The Production Branch of the Signal Corps Procurement and Distribution Division assigned an officer to coordinate the activities of the Monmouth Procurement District and of the New York ANEPA people. Also the Signal Corps helped the L. S. Branch Company, Newark, New Jersey, to get out sufficient antennas for the TRC-1.108 Mr. Link himself wrote General Harrison, head of Signal Corps procurement, that his firm was “putting shoulder to the wheel in an unprecedented manner in an effort to meet a technically impossible deadline. We still may not meet it in every sense of the word, but certainly will meet it in general or go down trying.” He said that he had set all other work aside, had asked his employees to work a 70-75-hour, 7-day week and that they had gladly agreed.109
Still production lagged, chiefly because of further changes the military wanted made in the sets, although the military refused to recognize this as the cause of the delay. Late in December Mr. Link replied to a pressure note from General Harrison:
We feel that it was mutually understood between all parties concerned, including the Signal Corps officials, that final models could not be made available until all technical details relating to the equipment could be effectively frozen in the minds of Signal Corps Laboratory officials, the Contracting Officers and ourselves. I believe you will agree that it was not a case of our organization being unable to produce models as scheduled or of our lack of desire to make these models available as much as it is a situation where numerous changes of minor nature have been made in the new equipment at the request of Signal Corps engineering authorities that have made it impossible to supply the final models up to the present time.110
By the late winter of 1944 the Link Radio Company was turning out AN/TRC-1 in quantity. The sets proved excellent. One report stated that “all results of tests made on subject equipment had been thoroughly satisfactory ... voice, teletype, and facsimile transmission had been put on the circuit hour
AN/TRC-6 antenna array is lowered for removal to another site
after hour without any interruption.” General Colton in August 1944 warmly thanked Mr. Link. AN/TRC-1, 3, and 4 “have been most valuable additions to our military communication equipment ... an invaluable means of communication comparing in efficiency, as a system, with regular long distance telephone pole lines.”111
The production rate of the sets, however, could not meet the rapidly growing need for military radio relay. “There was no question,” Mr. Link recalled years later, “that Link Radio did not have the mass facilities required to produce the unprecedented requirement for AN/TRC-1, 3 & 4 systems.” This fact, coupled with Army’s desire to decentralize the manufacture of so vital an item, led the Signal Corps late in the summer of 1944 to assign further production contracts to the Rauland and Lear Avia Corporations, located in Grand Rapids and Chicago, respectively, in order to augment the output of the Link Radio Company in New York City.
At the same time, the Army granted to the antrac manufacturers higher precedence than Link had previously had to obtain materials and components.112
AN/TRC-1, 3, and 4 constituted 4-channel radio relay, operating in the very high frequencies, VHF, in the 70- to 100-megacycle band. Each channel could carry one voice circuit or four teletypewriter circuits. The Army needed even more radio channels than this form of relay could offer. It was becoming necessary to move to higher and higher frequencies in order to obtain the needed band width—in the hundreds and thousands of megacycles. Radar tubes had been evolved able to emit pulsed radiations in those ranges of the frequency spectrum, far beyond the capabilities of FM oscillators at that date. It would thus be possible to devise methods of communicating by pulse modulation at radar frequencies.
This very thing was first done by the British. Early in World War II information had been received in the United States concerning an 8-channel timedivision multiplex pulse-modulated microwave (UHF) radio relay developed by the British as their wireless set No. X10A. In 1942 engineers from Signal Corps laboratories, Bell Telephone, and RCA laboratories had gone to England to examine the equipment. On returning they set about developing American versions, which became AN/TRC-5 and 6. About ninety sets of AN/TRC-6 were produced in time to serve in World War II. Operating at much higher frequencies than the 70 to 100 megacycles of AN/TRC-1, with greater band width, providing the capacity to handle more channels of communications simultaneously, AN/TRC-6 opened up whole new realms of possibilities, quite as FM techniques had done a few years earlier.113
This new radio relay species was neither FM nor AM. It employed one signal in the microwave region (SHF, Superhigh frequency) but it chopped that signal into eight pieces, one to a channel, providing eight channels simultaneously, twice the capacity of the TRC-1 equipment. The chopping progressed at lightning speed at the transmitter. The receiver put the pieces back together in perfect step with the transmitter. The technique, borrowing from radar and television, relied on precise time division of the signal in inconceivably minute bits, measurable in millionths of a second. This was a totally new method of communicating—radio pulse communications, pulse-modulated or pulse-position modulated, at the microwave frequencies of radar, at 4,300-4,900 megacycles. The almost infinitely minute bits of signal were, in a way, a return to the dits and dahs
of Morse, hand-keyed. Only the hand that keyed the time-division signals was the electron itself, moving at the speed of light, with infallible precision.
The Bell Telephone Laboratories delivered several development models to the Camp Coles Signal Laboratory late in 1943. In January 1944, the Air Forces outlined a tactical requirement for the AN/TRC-6 and asked for four service test models. Meanwhile the Coles Laboratory worked not only on the AN/TRC-6 but also on two other antrac types, AN/TRC-5 and 8.114
In June 1944, the Air Forces, impatient, requested that the Signal Corps stage a demonstration of its several antrac types. General Ingles replied that it would be done, not only for the Air Forces but also for the benefit of all interested arms. The Signal Corps would parade at Camp Coles AN/TRC-3, 4, 5, 6, and 8. He added that the Signal Corps had already let development contracts for 48 sets of AN/TRC-6, and for 91 sets of AN/TRC-8. Ingles intended that the AN/TRC-6’s be set up between the Aircraft Radio Laboratory in Ohio and the Signal Corps Ground Signal Agency in New Jersey, both to demonstrate a 600-mile radio relay line and to provide a good multicarrier communications link between these two widely separated halves of the Signal Corps research and development establishments.115
The Air Forces, close to accomplishing their intent to split the Aircraft Radio Laboratory away from the Signal Corps, were not interested in this unifying use of the new TRC-6. General Arnold wrote to General Somervell in July that the equipment could “better be used in active theaters.”116 And so it would be. AN/TRC-6 radio relay in the hands of the 3163rd Signal Service Company reached the European theater in time to carry very heavy traffic loads during the last months of the war and established the pattern of microwave pulse-modulated communications systems of the future.117
Air-Ground Radio
Another ground radio problem that combat experience intensified was airground liaison, in order to communicate directly between aircraft and ground forces, whether infantry, tank forces, or paratroopers. All these ground elements had gone into action early in the war without VHF radios, which alone could communicate with the VHF command radios used by all Allied aircraft, the SCR-522.118 “The history of air-ground
liaison and equipment. ... “ wrote Lt. Col. William S. Marks, a former civilian radio engineer at the Fort Monmouth laboratories, “has not been a very happy one. What there is has been learned in the theaters the hard way and accomplished with improvised installations.”119
Why had no provisions been made for such air-ground liaison? “The indicated policy,” Colonel Marks explained, “has been that the Air Forces will furnish and operate the radio set.” He traced the problem back to 1940 and the initiation of the Armored Force radio series. It was obvious even then that the German Stuka-tank teams coordinated their blows very successfully. Yet the SCR-506, Set II in Armored Force’s 500 series, was at first planned to be a continuous wave radio only, although it would be the logical set for use between Armored Force units and aircraft. However, Marks went on, “No consideration was given for operation with the air since that was a responsibility of Air Forces.” The need to communicate with aircraft repeatedly asserted itself, and, since aircraft command radios employed voice only, the design of the SCR-506 under development in 1941 was altered to include voice. It therefore provided a radiotelephone facility whose frequency range overlapped part of the high frequency range of the aircraft command set of that day, the SCR -274. This alteration delayed the SCR-506, and, when at last in 1943 production models began to reach the Armored Force, they could not communicate with the newest Air Forces command radios, the VHF type. “Probably,” Colonel Marks said in his 1945 review of the subject, the SCR-506 “has never talked with the air on a support mission.”120
The reason was that by 1943 the old high frequency aircraft command radio SCR5-2742 had 2yielde, d to the VHF SCR-of the 506, which remained only a high frequency radio. Despite this change in the aircraft command set, no ground arm had submitted characteristics for a companion radio to provide ground liaison in these very high ranges of VHF. Any proposal in that direction would have been an AAF prerogative, and no such proposal was forthcoming.
In the theaters, early combat tactics made it imperative that ground units be able to communicate directly with aircraft overhead. Combat troops had to improvise and they did. “The North African Theater,” explained Colonel Marks, “sent back reports of what was called a ‘Veep’ set, an SCR-193 and an SCR-522 installed in a jeep.” This became recognized in Signal Corps procurement and nomenclature; it became the AN/VRC-1, a hybrid development originating not with the laboratories but with field troops. General Colton called it the HF/VHF set. Thousands were ordered for infantry use and for joint assault signal companies.121
Thus at last the AN/VRC-1
improvisation could provide air-ground liaison, but only for the infantry, not for the Armored Force, whose tank radios were FM and could not communicate with the SCR-193 component of the “Veep” hybrids, which were AM. American tanks and aircraft still could not communicate readily with each other. If there was to be any contact, the communication had to move in the “proper channels of command”—if a tank unit wished to call aircraft to bomb a specific target, the tank commander would have to call his ground headquarters on FM, and the headquarters in turn would have to call up an Air Forces control center employing wire lines, or AM radio such as the 193, the 506, or the 299. Air Forces controllers then could direct aircraft over their VHF command nets, using the ground VHF transmitter components of the SCS-2 or 3 systems or the SCR-624.
Stark necessity in Normandy cut through this rigmarole, and tankmen somehow mounted the SCR-522’s in their juggernauts. “It is reported,” Colonel Marks wrote, “that the SCR-522 is installed in some manner in tanks. By whom, in what tanks, and how many is not known.” Colonel Williams, the First Army signal officer, subsequently explained in more detail that, when immediate fighter-bomber support was needed by ground forces at St. Lô, each armored battalion acquired an SCR-522. Before the St. Lô operation, he admitted, “communications for air support of ground troops were not very satisfactory. During the Normandy landings,” he added, “no quick adequate means of obtaining close fighter-bomber support were available.” At St. Lô, however, “each armored battalion was furnished with a VHF radio, SCR-522, the type installed in fighter bombers. This set was installed in the tanks which were to lead the armored columns. These tanks were in communication with fighter bombers immediately overhead as the advance took place.” Williams concluded, “the speed and magnitude of the breakthrough at St. Lô and the successful exploitation were due greatly to this close air-ground communications.”122
This was just what the Germans had done so successfully four years earlier. The lamentable fact that, despite the early example of the German tankbomber team, American tanks and aircraft could not communicate directly till necessity forced an improvisation might seem on retrospect, a delinquency on someone’s part. More likely the need was lost sight of in the fog of war preparations and organizational confusion.
In 1943 the Air Forces did rather belatedly request an air-ground liaison VHF radio, the AN/TRC-7, for the use of paratroopers. The Camp Coles Signal Laboratory developed it as a VHF set, with a range comparable to that of the SCR-522, broken into small packs the paratroopers could carry as they chuted to earth. The Air Forces tested the radio during the summer of 1944 and asked for 500 sets, crash-produced. “This is the first ground set developed specifically for ground-air liaison,” wrote Colonel Marks, concluding his rather unhappy history of this category of equipment. From his review of air-ground liaison history he deduced “the serious need of the Ground Forces to maintain active
liaison with the Air Forces on this subject.” Already both the Navy and the Air Forces were planning to develop another airplane set of higher frequency.123
Equipment Situation at the End of the War
Before World War II, Signal Corps equipment—wire and radio—had been designed to be rugged and simple, somewhat to the detriment of portability, and for use in the latitudes of the United States. Suddenly World War II took U.S. troops to all parts of the globe. It put communications equipment to increased use under extreme climatic conditions. Radio received much greater use than ever before, all the way down to the smallest troop units, where untrained men had often to rely on small portable sets. It therefore became imperative that equipment be waterproofed and tropicalized; that, while range and channel capacity be increased, weight be decreased; and that items be kept rugged and simple to operate. Meanwhile, many World War II items had to be developed by various commercial companies in order to hasten procurement. Specifications, hastily prepared, stressed performance while keeping to a minimum limitations on components and materials. As a result the Signal Corps could not achieve a high degree of standardization.124
So it was that the emergency character of Signal Corps research and development and supply in World War II spawned a sometimes unhappy mixture of equipment items, of individual components that, however excellent in themselves, were ill suited to work well in systems where effective coordination was needed. The “handie-talkie” SCR-536 infantry radio was AM and could not communicate with the walkie-talkie, which was FM. Tank radios were FM but their frequency range did not overlap that of the walkie-talkie, so that tank-infantry teams could not radio to each other. These obvious defects, which resulted from headlong production with its accompanying lack of thoughtful planning, clearly indicated a need for communications systems containing integrated and coordinated wire and radio items that could communicate with each other. “I felt there were weaknesses in the ground forces communications—not so much in equipment as in systems,” commented Dr. Bowles late in the war.125
One of Dr. Bowles’ civilian consultants, Albert Tradup, looked into the ground force communications problems from September 1944 to the war’s end. He studied in detail the many radio and wire nets of tactical troops. They were quite segregated—for example, a high frequency net from the infantry regiment headquarters to battalion headquarters, a VHF net from battalion to company, an HF net within the company, all three nets being entirely separate with no possibility of interconnection. To transfer a message from one
net into another, radio operators had to repeat it. Tradup therefore urged that equipment be developed that could connect dissimilar radio channels to each other and to wire channels. He urged reassignment of frequency band widths so that the infantry radios might occupy a central place, with a frequency overlap with artillery radios on one side of the infantry band, and with armored force radios on the other. He noted the glaring lack of a common radio channel between infantry and tank radio sets. A start had been made to remedy this with the AN/VRC-3, a tank radio (40- to 48-megacycle, FM), which could communicate with the walkie-talkie SCR-300. For some time, too, the telephone set AN/VIA-1 had been in use, attached to the outside of a tank, over which an infantryman could reach the crew through the interior interphone system. But such solutions only created additional separate items of equipment, not ideal solutions.126
This confusion of Army’s radio sets and types (and of wire components too), this array of individually good but collectively unrelated equipment items of World War II, pointed to the necessity that the Signal Corps must engineer the many sets and components to work together in a coordinated system wherein all might intercommunicate. This need was beginning to be formulated by such men as Tradup at the war’s end.
Along with engineering of systems and integration of equipment, begun before the end of the war and certain to go on long afterwards, was miniaturization. Always in the military there is pressure to make equipment small, compact, light in weight. In communications electronics there was room for much improvement; small components enable smaller sets; tubes could be made smaller, and so on. Tradup mentioned the importance of this in his wartime reports. Nowhere were the possibilities more evident than in the case of field switchboards—in the excessively heavy regimental and battalion BD-71, for example. In the modulelike plastic units of the SB design was an omen of the form that future communications electronics equipment might take. And more communications would be needed. Tradup noted that the six drops of BD-71 were not enough for the growing communications needs of a battalion. He recommended 8 or 10. The subsequent SB-22 would have 12.127
FM had proved itself entirely in the tactical communications of close combat. Yet not all short-range combat radios were FM. For example, the “handietalkie” was an AM set, SCR-536. So was the guidon set, SCR-511. Neither could talk with the walkie-talkie, SCR-300, an FM set. Before the war was over, work had begun on the FM successor to the SCR-536, the AN/PRC-6. The SCR-536 was a good example of the individual sort of set that was so often rushed into production during the war, without coordination with other sets.
Another good example was the much used long-range SCR-299 (and 399 and 499). At war’s end Signal Corps laboratory engineers were beginning to think of families of radio sets that could work together, and that could serve all arms, with such slight variations as frequency coverage; they began to think of radio and wire equipment that could work together, or interchangeably, through the same switchboards. Whether a message might travel partly by wire, partly by radio, did not matter so long as the operations of the equipment all meshed well. The first, and most likely line of action for the laboratories to follow in the future, a 1945 SCEL report stated, was “to improve existing standard equipments by designs which lead to integration of facilities, greater flexibility, and mobility, lower weight and bulk, interchangeability, and over-all standardization.”128
In radar, the defects of early sets—insufficient accuracy, poor discrimination, poor height finding—were largely overcome by microwave developments that increased the range of reliable detection at all heights and gave accuracy comparable to optical methods in automatic tracking and gun laying. At the end of the war the Signal Corps Engineering Laboratories reported, “the present trend is towards the development of smaller and lighter-weight microwave radars using the same basic principles.”129 One innovation was doppler techniques. Radars had been harassed by ground clutter in the detection of low-flying objects, and in fire control against them. By mid-1945 doppler techniques were being introduced in search sets but had not yet improved sufficiently for use in fire control.
The application of radar techniques to ground targets such as tanks and other vehicles was most difficult, indeed hardly possible till microwave radar arrived. Ground applications were badly needed in the last years of the war when the problem of locating enemy mortars became paramount, taking precedence over all other ground uses of radar. Mortar fire was causing a large percent of battle casualties. The problem began to be solved upon discovery that several types of existing radars, especially the SCR-584 and the AN/TPS-3, could locate enemy mortars by getting fixes, by means of radar reflections, on mortar shells at several points along their high arching trajectories. The Camp Evans Signal Laboratory first undertook in 1943 to adapt the TPS-3, altering it as the AN/TPQ-3. The Radiation Laboratory of OSRD would not accept the mortar location assignment, Dr. Zahl recalled years later, because of the belief that the problem could not be solved before the war ended. But the Signal Corps accepted the challenge to crash-build some sets. In Zahl’s words:
The Laboratories took it up, worked hard for several months culminating in a show of unbelievable enthusiasm, when Captain Marchetti led his task force through 4 consecutive days of almost 24 hour effort, with occasional catnaps and food brought to them. Bleary-eyed, the bearded engineers ... left building 20 at Camp Evans after almost 96 hours of continuous effort, almost ready to collapse but
mortar locating radars were on their way to the Pacific.130
In 1944 the Camp Evans Signal Laboratory began the design of special mortarlocating radar, the AN/TPQ-2. Its sharp beams could also locate enemy troops and vehicles under favorable conditions. Preproduction models were just being completed as World War II came to a close.131