The irrepressible Serbian-American inventor Nikola Tesla raised the basic idea of radar as early as 1900 and formally incorporated it in a 1905 US patent application. A lower-profile inventor named Christian Hülsmeyer, picking up on findings by his own countryman Heinrich Hertz, applied for a similar German patent in 1903–1904.26 And Guglielmo Marconi, the electrical engineer and entrepreneur whose name is inseparable from the early years of radio communication, discussed the idea in 1922 in New York, in an address to fellow engineers:
In some of my tests, I have noticed the effects of reflection and deflection of [radio] waves by metallic objects miles away.
It seems to me that it should be possible to design apparatus by means of which a ship could radiate or project a divergent beam of these rays in any desired direction, which rays, if coming across a metallic object, such as another steamer or ship, would be reflected back to a receiver screened from the local transmitter on the sending ship, and thereby immediately reveal the presence and bearing of the other ship in fog or thick weather [and] to give warning . . . , even should these ships be unprovided with any kind of radio.27
“Give warning” is a phrase brimming with military potential. In the early months of World War II, radar was already being deployed for that purpose in much of the world: Europe east and west, North America, Japan. It was used in South Africa; it was used in the Aleutian Islands. “World War II was the first electronic war, and radar was its prime agent,” writes historian Andrew Butrica. “Despite its scientific origins, radar made its mark and was baptized during World War II as an integral and necessary instrument of offensive and defensive warfare.”28
In A Radar History of World War II, on the first page of his preface, physicist Louis Brown proposes that “science and war . . . are unquestionably the two most dissimilar manifestations of the behaviors that distinguish man from beast.” But dissimilarity does not preclude marriage:
[W]ar is almost as unique to man as is science. Other than ourselves, only ants organize their violence so that it can be called war. . . . Moreover, from the dawn of civilization science and war have been inseparable companions, locked in a partnership that neither desires and that neither is capable of dissolving.29
On both the Allied side and the Axis side, that brand of co-dependence produced military radar. “No weapon,” writes Brown, “was ever designed with such intimate collaboration between inventor and warrior.”30 The collaboration, however, was neither automatic nor stress-free. Before their work was officially embraced, not only did radar researchers and advocates face political and institutional roadblocks at several junctures, but their work was also, at first, occasionally sidelined by advocates of other rudimentary technologies competing for primacy: acoustic location and infrared detection. Added to this mix were turf skirmishes between armies and navies and the spotty scientific literacy of key decision makers.31
During the first third of the twentieth century, scientists across the Northern Hemisphere were developing components and materials that would eventually enable not only radar but television as well. Foremost among them were cathode-ray vacuum tubes (fused silica was the solution) and insulation for high-frequency cables (polyethylene was the solution). Much of their effort took place at large companies such as DuPont, General Electric, and IG Farbenindustrie AG and was initially spurred by the civilian radio boom rather than by military demands. By the 1930s in Britain, France, Germany, Japan, the Soviet Union, and the United States, the “brothers-in-arms” at military laboratories, electronics corporations, universities, and research institutes were all investigating possibilities for effective radiolocation. Radar was “in the air” as Adolf Hitler became Führer and Germany rearmed.32
The direction and pace of radar work varied considerably from country to country. While Britain, for instance, initially focused on defense,33 Germany focused on offense. While the British government actively sought out scientists and new approaches to weaponry, the German government didn’t act until engineers sought out officials and staged demonstrations for them. While Britain put a lot of energy into the development of organizational capability, Germany emphasized the development of sophisticated radar technology and the maintenance of secrecy. Indeed, the secrecy was so extreme that the Kriegsmarine (literally, “War Navy”) initially objected to even showing its technology to the Luftwaffe (“Air Weapon”), let alone sharing it, and resisted placing radar officers or even radar instruction manuals on its ships.34
At the start of the war, Germany already had three main advanced radar designs, though few of each were in operation. The Kriegsmarine’s Seetakt, a surface-search radar for use on warships and in coastal defense, focused on accurate ranging; the Luftwaffe’s Freya was a longer-wavelength, mobile air-warning radar for land use that could register targets at greater distances than Seetakt could; and Würzburg, a highly accurate targeting radar, was especially useful for anti-aircraft guns. As World War II escalated, manufacturers came up with variations small and large.35
Britain had determined from military exercises during the early 1930s that the nation would be defenseless against an air assault from the modern, all-metal bombers that were rolling off the line in Germany. Some members of the British government quickly grasped radar’s strategic possibilities and were willing to commit major resources and personnel to immediate military-radar research and implementation—a commitment not exposed to public discussion in either the Commons or the press. As of July 1935, British radar technology could detect a plane forty miles away; by March 1936, that number had risen to seventy-five. As of late 1937, three early-warning radar stations were operational; by September 1939, a network of twenty, called Chain Home, had been installed along Britain’s coastline. A year later, on September 15, 1940, at the height of the Battle of Britain, Chain Home operators helped down so many German planes that the Luftwaffe soon abandoned the large-scale daytime sortie in favor of the nighttime blitzkrieg, plus occasional daytime attacks on specific targets. Germany’s plan to invade Britain had to be dropped.
Although the Germans and Americans had superior equipment at the start of the war, the British had done advance threat assessment, chosen a defensive system that could be quickly built, partly reorganized their military forces around the precept of homeland security through radar, and mobilized as well as trained more radar operators—including hundreds of women—than all the other radar nations combined. Swift, concise communication was key. As Brown writes, Britain “had the wisdom to realize that intelligence gained by radar was worthless unless promptly interpreted and acted upon.”36
But of course, equipment is hardly irrelevant. Underlying the technological side of Chain Home’s contribution was a technique, developed in the mid-1920s by American scientists, for measuring the height of the reflective portions of the ionosphere by sending up several-millisecond pulses of radio waves and clocking the duration of the return trip. The UK’s Radio Research Board, acting at the behest of the Committee for the Scientific Survey of Air Defence from early 1935 through the end of the war, adapted the technique for purposes of protecting the homeland.37 Among Chain Home’s numerous challenges were distinguishing friendly from enemy aircraft, detecting aircraft that were flying low and close to the coast, providing accurate altitude readings for incoming aircraft, and coming up with accurate counts of enemy aircraft. Chain Home alone couldn’t do the job. It needed partners: radio direction-finding sets, good radio telephones, and all those civilian radar operators.38
However, a radar ground installation, operating at wavelengths of a meter and a half and transmitting information in short, clear code words to a fighter pilot whose plane was equipped with a radio telephone, could still not provide enough input to enable a British pilot to destroy a German factory, bomb a U-boat, or shoot down a German bomber headed for London in the dark of night. In addition to input from the ground, that pilot would need—on board—a powerful, lightweight, high-frequency device that could serve as a type of searchlig
ht and detect a target in darkness or in fog. This new device could not rely on the same kind of lower-frequency radar that had proved so useful when looking upward from ground level, because, when looking downward from the air, radio energy reflected from Earth itself would swamp the fainter radio echoes bouncing off the enemy craft. Moreover, it had to be portable. Solution: microwave radar, produced by a so-called resonant cavity magnetron. A British version—brought to the United States in a supersecret mission in September 1940—was described by President Franklin D. Roosevelt as “the most important cargo ever brought to American shores” and by A. P. Rowe, superintendent of Britain’s Telecommunications Research Establishment, as “the turning point of the war.”
Those statements, it turns out, are only half true. Not only had extensive work been done on microwave radar during the 1930s, but magnetrons of other sorts already existed. The cavity magnetron had been patented by Russians in the 1920s and was already known to the Germans. By the end of the 1930s Japan, too, had them. It’s just that the British didn’t know about these devices, and the Germans were being ordered to shelve theirs and to concentrate on longer-wavelength radar.39
And so, British scientists independently reinvented the invention, and soon Americans sought to improve it. By the spring of 1941, less than a year after the unnecessarily secret mission, the newly created MIT Radiation Laboratory in Boston had produced a three-centimeter version of the resonant cavity magnetron. The Cambridge-based company Raytheon soon began manufacturing most of the magnetrons used in the war effort by both the United States and Great Britain.40 In fact, the now-indispensable microwave oven can be traced to a Raytheon engineer, Percy Spencer, who found that a candy bar in his pocket had melted because of the microwaves emitted by an active magnetron he’d been standing near.
Concurrently, the US Navy and the US Army Signal Corps were working on longer-wavelength radar, and on December 7, 1941, one of the new mobile radar units in the Army’s Aircraft Warning System detected Japanese planes approaching Pearl Harbor almost an hour before the attack. The warning was ignored, and the source of the radar echoes was misinterpreted as B-17s, friendly bombers scheduled to arrive from California that very day.41
Unknown knowns also affected the course of the radar war. At certain points in the conflict, one side seemed not to know that the other had effective radar. One telling example of this was the swift Japanese evacuation of the Aleutian island of Kiska in the summer of 1943 during an American naval blockade—an evacuation carried out in heavy fog and made possible by a determined Japanese admiral relying on Japan’s new microwave radar, of which the United States was unaware.42
Whatever its failures and limitations, radar in a range of incarnations did play a big part in both the Allied and the Axis campaigns. On the Allied side, a popular claim was that the bomb had ended the war but radar had won it—by locating and helping to destroy enemy bombers in darkness, enabling aircraft to “bomb blind,” maximizing the accuracy with which anti-aircraft artillery could be aimed, enabling a plane to map the ground or water surface over which it was flying, and, of course, reducing the navigational difficulties posed by the presence of fog and the absence of light. Early in the war, however, accurate aim in blind bombing was still unachievable. So, the precise, selective destruction of German industrial targets such as factories was out of the question. The only obvious alternative was to bomb larger areas. “Translated into practical terms,” writes Louis Brown, stressing what the limits of technology can force you to do, “this meant that the targets would have to be of city size.” Hence, the air war against Germany turned into the destruction of its cities rather than, as initially strategized, the elimination of its synthetic oil production.43
As soon as writers were permitted to discuss radar publicly in detail, a note of hyperbole occasionally crept into Allied accounts: “perhaps the war’s most fabulous and zealously guarded secret”; “Warfare today would be more or less impotent without this modern electronic genie”; “the great drama of radar, the war’s most powerful ‘secret weapon’ until the atomic bomb was devised.”44 In early 1946 the British radar pioneer Robert Watson-Watt spoke of “that secret weapon which prevented the cutting of our life-line, which would have resulted had the defeat of the U-boat not been assured.”45 Winston Churchill’s assessment was more nuanced: “it was the operational efficiency rather than novelty of equipment that was the British achievement.”46 But whether a great drama or simply an achievement, radar changed war by making the invisible visible. Decades later, Louis Brown would assert that the “introduction of radar, a completely new way to see, in the Second World War altered the basis of warfare more profoundly than any of the inventions that had marked the industrialization of combat.”47
Yet for planetary astrophysicists, radar also affords a way to track potentially hazardous asteroids that could render humans extinct—the ultimate defensive application of this technology, an agent not of warfare but of survival.
With hostilities ended, rafts of journalists, politicians, warriors, and citizens applauded the proven military benefits of radio waves. They also honored the scientists and engineers who had made those benefits possible. Many scientists launched or resumed their radar research into the ionosphere, and military planners began to think about improved radar countermeasures in the context of new kinds of long-distance battle threats. The stage was now set for even greater and more intricate cooperation between the practitioners of science, the advocates of war, and the seekers of profit.
During and immediately after the war, there was already widespread sharing and borrowing between scientists and warmakers.48 Initially, radar scientists supplied the armed forces with basic techniques, while the armed forces, often working with major corporations and universities, undertook large-scale science and technology programs to adapt those techniques for use in militarily beneficial technologies. After the war, radar astronomers further developed the techniques, while private industry attracted many scientists whose skills were no longer required for war work. Former adversaries became allies, and vice versa. The Iron Curtain descended, and Cold War projects multiplied. Postwar research in the radio band swiftly ramped up as astronomers outfitted their observatories with wartime radar surplus, often bought at fire-sale prices or simply rescued from being thrown down a mineshaft. The Jodrell Bank Observatory was furnished just that way.
Early in 1946 radar astronomers at a US Army Signal Corps facility in New Jersey succeeded in bouncing radio waves off the surface of the Moon. Within a month, Hungarian physicists did the same. British researchers found a correlation between their visual sightings of meteors plunging through Earth’s atmosphere and the radar echoes that registered on their equipment during the meteors’ fiery journey. Through close analysis of paths and velocities, researchers in Britain and Canada determined that detectable meteors are inhabitants of our solar system, not invaders from beyond. Several groups in several countries obtained radar echoes from Venus.49 Researchers from former enemy nations resumed the normal scientific practice of collaboration—a noteworthy (though later) example being Bernard Lovell, director of Jodrell Bank, and the very same German radio astronomer who in May 1943 had investigated and reported on the blind-bombing radar equipment aboard two downed British bombers.50
Ionospheric research contributed to progress on secure, point-to-point, long-distance communication, a goal high on the military’s wish list—then and now. In the United States, significant funding and activity came from the Central Radio Propagation Laboratory division of the National Bureau of Standards (nowadays called NIST, the National Institute of Standards and Technology) and from military organizations such as the Air Force Cambridge Research Center, the Army Signal Corps, and the Office of Naval Research. Corporations big and small—ITT (International Telephone and Telegraph), RCA (Radio Corporation of America), the Collins Radio Company of Cedar Rapids, Iowa—were also part of the push. In this milieu, astronomers at Stanford University, the Naval Re
search Laboratory, Jodrell Bank, and elsewhere explored possibilities for radio-wave communication between Earth and the Moon, including the idea of bouncing signals off the lunar surface. By 1951, several groups of investigators had achieved long-distance wireless voice transmission via the Moon, which they used as a passive relay—a naturally occurring, cost-free, pre-Sputnik satellite.51
In the meantime, scientists, generals, futurists, political leaders, and university-based military contractors here, there, and everywhere—from Arthur C. Clarke to Josef Stalin to Project RAND—were thinking hard about rockets.
It was old news that this invention, capable of piercing the ionosphere, could serve equally well as a conduit to space and an agent of terrestrial devastation. Already in the fall of 1931, five years after Robert Goddard demonstrated his first liquid-fuel rocket, a high-school dropout turned MIT engineering graduate named David Lasser, first president of the American Interplanetary Society, could confidently declare to an audience at the American Museum of Natural History in New York: “The perfection of the rocket in my opinion will give to future warfare the horror unknown in previous conflicts and will make possible destruction of nations, in a cool, passionless, and scientific fashion.”52
Often camouflaged, barely trackable, and inaudible at its target due to its terrifyingly swift supersonic speeds, Germany’s V-2 rocket had proved second to none in how technology can deliver terror, and so the United States and the Soviet Union both scrambled to seize small armies of German V-2 rocketeers and shiploads of V-2 rocket parts even before World War II had run its course.53 Both sides set themselves the task of making a more deadly version of the V-2: a long-range, high-speed missile with a nuclear warhead at its tip, rather than a traditional explosive. Yet at the same time, both sides understood the value of a V-2 pointed beyond Earth’s atmosphere toward outer space. Even Wernher von Braun, the life force behind the V-2 rocket, famously quipped in 1944, after the first direct V-2 hit in London, “The rocket worked perfectly except for landing on the wrong planet.”54
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