Late in 1939 Nazi Germany was poised to overrun Europe and extend Adolf Hitler’s fascist control. At the same time, however, two British physicists invented the resonant cavity magnetron. About the size of a hockey puck, it unlocked the enormous potential of radar exclusively for the Allies.
Since the discovery of radar early in the twentieth century, development across most of the world had progressed only incrementally. Germany and Japan had radar as well, but in just three years, the Allies’ new radar, incorporating the top-secret cavity magnetron, turned the tide of war from doubtful to a known conclusion before the enemy even figured out how. The tactical difference between the enemy’s primitive radar and the Allies’ new radar was similar to that between a musket and a rifle. The cavity magnetron proved to be the single most influential new invention contributing to winning the war in Europe.
Norman Fine tells the relatively unknown story of radar’s transformation from a technical curiosity to a previously unimaginable offensive weapon. We meet scientists and warriors critical to the story of radar and its pressure-filled development and implementation. Blind Bombing brings to light two characters who played an integral role in the story as it unfolded: one, a brilliant and opinionated scientist, the other, an easygoing twenty-one-year-old caught up in the peacetime draft.
This unlikely pair and a handful of their cohorts pioneered a revolution in warfare. They formulated new offensive tactics by trying, failing, and persevering, ultimately overcoming the naysayers and obstructionists on their own side and finally the enemy.
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About the Author
Norman Fine is a retired electronics engineer, founder of a high-tech company, and the editor and publisher of an annual engineering design guide series in the 1990s.
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The Death Ray
Throughout World War II, most of the combatant nations had radar. British radar detected and tracked flights of German bombers headed toward England and vectored British fighters to intercept them. German radar tracked approaching Allied bomber formations, and Japan's Imperial Forces with Japanese-designed radar detected U.S. warships.
The Allies, however, had microwave radar, thanks to the British invention of the resonant cavity magnetron. That invention provided scientists with the single device that unlocked radar's enormous potential, just as the rifle superseded the performance of powder and ball. And possession of the resonant cavity magnetron, a closely guarded secret, produced two critical turning points in the Allies' prosecution of the war.
First, microwave radar detected German U-boats and pushed them from both the coastal waters off North America and the shipping lanes to England. In the early and most perilous months of the war, the German High Command of the Navy was repeatedly mystified by its own inexplicable reverses on the seas. Second, by January 1944, with a tiny fleet of microwave radar–equipped Allied bombers actually seeing through the thick cloud cover and leading the bomber formations, the Allies no longer had to scrub bombing missions most winter days. In just six months, their bombers crippled Germany's war-making infrastructure and decimated the Luftwaffe. The D-Day landings in Normandy could not have happened otherwise.
The discovery of radar, as with many other important innovations, was accidental. Around the turn of the twentieth century, scientists in developed countries who were working on radio communications noticed that radio signals faded in and out when a large object, such as a ship, passed between the transmitter and the receiver. Later, in the 1920s, scientists noticed the same fluctuations in signal strength when planes flew past. (Television viewers who can remember picture tube sets will recall nearby passing airplanes caused annoying flickers on their TV screens.)
For most scientists, the signal fluctuations were simply a nuisance, just as they later were for television viewers. A few, however, were sufficiently intrigued to speculate on the cause. They concluded that radio transmissions, like light, could be reflected by the surface of large objects — just as sound is reflected from a large surface as an audible echo.
A few scientists around the world foresaw the application of this phenomenon to the detection of enemy ships in the event of war, but their military establishments mainly ignored them. In the summer of 1930, Lawrence Hyland, a young associate radio engineer at the U.S. Naval Research Laboratory (USNRL), noted radio signal reflections off planes and pursued radar research in his spare time using his own funds. His work eventually stimulated further radar development at USNRL for the navy — as well as the U.S. Army — with each branch pursuing its own purposes independently through the latter half of the decade. In the private sector, three engineers at Bell Telephone Company published a paper in the Proceedings of the Institute of Radio Engineers in 1933 describing how a sensitive radio receiver detected signals reflected from an aircraft passing overhead.
In London in 1915, a recently graduated electrical engineer named Robert Watson-Watt was invited to join the Meteorological Office. The director, Dr. William Napier Shaw, believed that timely thunderstorm warnings would be of value to aviators in the infant Royal Flying Corps. Shaw's idea was to track thunderstorms by radio. (Some will remember when lightning produced static in AM radio reception.) One of Watson-Watt's tasks, in addition to day-to-day weather reporting at the Royal Aircraft Establishment, was to unravel the mystery of radio "atmospherics" — those explosive bursts of electronic energy transmitted by lightning — and try to use them to warn pilots of storms in their paths. For twenty years, Watson-Watt, who was later acknowledged as the father of radar in Britain, studied and explored radio atmospherics. He developed equipment capable of revealing the direction and distance of storms and weather fronts that proved useful to the Royal Air Force (RAF). In 1933 he was appointed superintendent of the Radio Department of the National Physical Laboratory, where he was approached soon after by Harry Wimperis, the director of scientific research at the Air Ministry, with a bizarre request.
Concerned about the growth of fascism in Germany and the future prospect of enemy air attacks and wishing to evaluate all possible means of defense (however improbable), Wimperis asked Watson-Watt if it was feasible to transmit some sort of "damaging radiation" directed at enemy aircraft or their crews. In other words, could he build a death ray?
Watson-Watt's creed as a scientist rested, as he himself later wrote, on "an almost religious conviction about the goodness of measured facts, that all facts are good: they may be facts about bad things, but if they are facts they are good and valuable." So even though the surprised scientist instantly felt the idea was futile, he promised to have calculations performed on how much energy could practicably be transmitted over distance and what level of energy might be required to inflict damage on enemy personnel or equipment.
Even though the calculations confirmed Watson-Watt's initial reaction, he prepared a memorandum for Wimperis in January 1935 pointing out that even if it were possible to produce and transmit energy levels high enough to "make the pilot's blood boil," the backward leakage radiation from the transmitter would prove far more dangerous to nearby operators than the forward radiation would be to distant targets.
While his memorandum deflated Wimperis's hopeful, albeit misguided, idea for defense against enemy aircraft, Watson-Watt's prior work on detecting weather fronts encouraged his own belief that aircraft detection, as opposed to destruction, by radio waves might be a more fruitful avenue of inquiry.
Although he hadn't been asked to consider the problem of detection, he closed his memorandum with a convoluted sentence using a double negative to produce a positive: "Meanwhile attention is being turned to the still difficult but less unpromising problem of radio-detection as opposed to radio-destruction, and numerical considerations on the method of detection by reflected radio waves will be submitted when required."
A kindly and charismatic man, Watson-Watt was noted for his confusing syntax. "When he was in good form, words bubbled out of him like a fountain, usually very long words in convoluted sentences," wrote Hanbury Brown, a scientist who was to work under him. "I watched him paralyze the Chiefs of Staff in Washington by telling them that, contrary to what they might think, he had not retired into 'putative innocuous desuetude.'"
To his everlasting credit, Harry Wimperis at the Air Ministry was able to decode Watson-Watt's syntax, could comprehend the significance of his theory, and indeed did "require" the proposed "submission." Calculations were performed, and under a covering letter dated February 12, 1935, Watson-Watt submitted a memorandum titled "Detection of Aircraft by Radio Methods." He postulated that by transmitting a continuous curtain of radio waves through which approaching enemy planes must travel, the tiny radio signals reflected could reveal the target's compass bearing (direction), range (distance), and angle of elevation from the horizontal (height). The memo not only described how the three quantities — direction, distance, and height — could be measured but also predicted the ability to "lock on" to a target, to track a target automatically, and to distinguish between enemy and friendly aircraft. Sir Henry Tizard, one of Britain's top scientists, later described this incredibly farseeing document as the very origin of the development of radar in Great Britain.
In explaining the principles of radar to his government's ministers, Watson-Watt might well have used an example from the natural world. Bats, flying blind, emit periodic screeches — sound waves at frequencies slightly higher than the range of human hearing. Their large ears collect the tiny reflections — sound echoes — of their screeches from obstacles in their path so they can avoid them and from flying insects so they can intercept and eat them. That is perfectly analogous to radar in action, with the main difference being that radar equipment transmits bursts of radio waves rather than sound waves.
In a matter of months, a team of bright young English scientists was recruited for the highly secret purpose of implementing a system to warn their nation of enemy attacks from the air. Watson-Watt was assigned to direct the efforts. While his decision to use young, inexperienced physicists rather than experienced radio engineers almost led to disaster, in the end it resulted in originality and speedy implementation.
Edward G. "Taffy" Bowen was one of the first of the young physicists recruited for the project. Bowen would become a productive and continuous thread throughout the development of radar; he was a central figure in the hands-on development of radar in England and ultimately in the United States. He joined the staff of the Radio Research Station in April 1935 and was handed a copy of Watson-Watt's farseeing memorandum to read overnight. The memorandum was enclosed in double envelopes, and Bowen was instructed not to let it out of his sight.
Bowen later wrote,
I was staying for a few days at the Manor Hotel at Datchett. That night I ate a solitary dinner with the envelope concealed in an evening newspaper on the table in front of me. After dinner, I went back to my room to study the manuscript. Before retiring to bed a few hours later, I felt the need for a nightcap and realizing I could not take the envelope down to the bar, I looked around for a good place to conceal it. Clearly, a drawer or cupboard was not good enough. I seized on what I thought was a simple solution and slid the envelope between the sheets to the bottom of the bed. It was quite flat and could not possibly be noticed.
I came back to my room, prepared for bed and checked that the memorandum was safely in its place; sure enough it was still in the same position, with a hot water bottle placed neatly on top of it. That night I had nightmares about swinging on the end of a jibbet on some lonely heath outside London. Next morning I made a point of chatting with the chambermaid and was relieved to find she bore no resemblance to a Mata Hari but was a buxom country girl with an unmistakable Buckinghamshire accent. This episode would not be the last of Bowen's comic adventures in trying to protect his nation's secrets.
For security purposes and to control access to the new Radio Research Station, Orford Ness in Suffolk — a narrow spit of land just off the southeast coast of England — was chosen for the field experimentation. And in order that those monitoring the team's radio transmissions might not divine its ultimate goal, the work was described as "ionospheric research."
Headquarters for the research laboratories and living accommodations for the growing team were established on the mainland at nearby Bawdsey Manor, a fairy-tale mansion built at the turn of the twentieth century and later purchased by the Air Ministry. High on a bluff over an estuary of the River Deben, which flowed into the North Sea, the magnificent structure contained an astonishing array of towers, turrets, and spires in a variety of architectural styles. The property provided an idyllic setting for the scientists, who, in the earlier and less urgent months of their occupancy, often unwound after long days and nights of mental labor with a morning swim, fencing, tennis, cricket on the expansive lawns, or tending the formal gardens.
The splendor of Bawdsey Manor notwithstanding, laboratory conditions on the island were primitive. Equipment was jury-rigged, and electronic parts and supplies were scarce. The requisitioning procedure for ordering a small radio component costing one penny was the same as for an aircraft engine. One crucial electronic component needed for the transmitter, a variable condenser, was made by fitting two ordinary metal cans of different sizes one inside the other. There was no workshop, but Hanbury Brown was tasked with building an antenna. One of his first steps was to drill a large hole in a wooden mast. He walked across the derelict World War I airfield to negotiate the loan of a brace and bit from the caretaker of the bombing range.
As I feared, he had the usual dislike of foreigners [Brown was English but not from there!] and, far worse, had taken to the appalling paperwork of the Air Ministry like a duck to water. It took me the best part of a half an hour to persuade him that I was on legitimate Air Ministry business and had not landed on that god-forsaken island to steal a brace and bit. Even so, he made me sign two separate loan forms in triplicate, one for the brace and another for the bit [each of which is useless without the other]. He then demanded that these valuable tools should be returned to his "store" before nightfall; if I wanted them the next day, he would reissue them, in triplicate, of course. I bored that hole, but it took me most of the day and permanently undermined my faith in the administrative ability of the people in charge of the early development of radar.
About a month after work commenced at Orford Ness, it was decided that Sir Henry Tizard and members of his Committee for the Scientific Survey of Air Defence should witness the first detection experiments. As the team tuned up the system in preparation for the committee's visit, the men saw signals reflected from passing aircraft.
On Saturday morning, June 15, 1935, committee members toured the station and were briefed on what they were about to see. That afternoon an RAF plane was sent to fly through the antenna's radar beam. Although the equipment seemed to be working perfectly, it detected nothing conclusive. On Sunday, another flight was made, but with abysmal atmospheric conditions for radio reception, the tests failed once again. Thanks mainly to Watson-Watt's diplomacy and salesmanship, the committee departed undismayed.
On the following day, Watson-Watt, who had remained at Bawdsey, witnessed a dramatic breakthrough. Perhaps atmospheric conditions improved; perhaps the crude, marginally operating equipment decided to cooperate. With no RAF plane dispatched to aid in the experiments, the equipment detected a twin-engine biplane independently engaged in bombing-run exercises near the coast at a range of seventeen miles and tracked it up and down the coast as far as twenty-nine miles. More successes followed, and by the end of the summer, construction of a national radar defense shield was being planned. In the autumn of 1935, the first of a coastal chain of radar antenna towers forming Britain's historic Chain Home system was erected at Orford Ness. That system was used throughout the war to provide an early warning of approaching German bombers.
As Britain began constructing its defensive radar chain, Lufthansa Airline crews soon noticed the rising 350-foot steel antenna towers. Agents were sent from Germany on the commercial flights, but even with their binoculars peering out the windows, they did not discern the purpose of the new British antenna construction. The Germans, already knowledgeable about radar, wanted to know more. Since the spreading construction effort was centered at Orford Ness and the seaside manor area was known to tourists, German agents were sent to camp out in the surrounding woods. They arrived with radio equipment in their backpacks but returned home none the wiser, learning nothing from their weak, portable radios or perhaps from searching the wrong frequency bands.
Luftwaffe commander Hermann Göring, distracted by other more concrete needs, displayed little concern, but Gen. Wolfgang Martini, the director of radio signals for the Luftwaffe, still wanted to know the purpose of the towers. Since hikers couldn't carry the appropriate heavy radio equipment, and the Lufthansa planes couldn't hover, Martini argued for a fleet of twelve airships to fly up and down the English coast with radio equipment to monitor the towers' transmissions. He was granted the use of two mothballed zeppelins.
The Graf Zeppelin II was a sister ship to the Hindenburg, which crashed and ignited in a fireball at Lakehurst, New Jersey, while docking to a mooring in May 1937. Thirty-five persons aboard perished, and virtually everyone in the world saw photographs that spoke to the terrible inflammability of hydrogen-filled airships. Germany retired its zeppelins, and after a year of neglect in its mammoth storage shed, the Graf Zeppelin was reactivated and sent to the English coast with its cupola filled with radio receivers. The Germans hoped to determine the transmission frequencies and other signal characteristics of the huge antennas. British radar quickly detected the huge airship, first believing it to be a formation of planes. After tracking it for a while and determining its airspeed, the British realized it was too slow for a plane and deduced it was a blimp.(Continues…)
Excerpted from "Blind Bombing"
Copyright © 2019 Norman Fine.
Excerpted by permission of UNIVERSITY OF NEBRASKA PRESS.
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Table of Contents
List of Illustrations Preface List of Abbreviations and Terms Prologue: Scientists and Warriors Part 1. Science and Politics 1. The Death Ray: 1930s 2. Europe in Turmoil, America in Denial: 1940 3. “A Four-Star General in Civilian Clothes”: 1939–40 4. The Tizard Mission: 1940 5. MIT Radiation Lab, Shanghaiing the Physicists: 1940–41 Part 2. The U-Boat 6. Airborne Radar and the U-Boats: 1935–41 7. From Defense to Offense: 1941–43 Part 3. The Weather 8. The Case for Blind Bombing: 1942–43 9. Relentlessly, despite the Weather: 1943 Part 4. Setting the Stage for D-Day 10. Getting to D-Day: 1943–44 11. Deep Penetration Bombing Losses: 1943 12. Scarcely a German Plane in the Sky: June 6, 1944 Epilogue: “Never a Tail-end Charlie” Acknowledgments Notes Bibliography Index