At that time, late in 1939, Randall lived in a small Worcestershire village not far from Barnt Green, and would share occasional commutes to the Edgbaston campus with Oliphant in the professor’s ageing Morris. During those half-hour car rides, the men discussed Randall’s evolving theory on the application of the magnetron, and during one journey Oliphant agreed it was worth a trial. Randall had recently happened across a dog-eared translation of Heinrich Hertz’s 1893 German text Electric Waves at a second-hand bookshop, a chance find that yielded inspiration’s spark.
Randall figured that if the gaps between the identical cavities drilled through the copper core were carefully calibrated, they would replicate the effect of a series of side-by-side Hertz oscillators. Electrons set in motion by means of a heated tungsten-wire cathode that ran through a separate hole of the same diameter (around 1 centimetre) at the centre of the ring of cavities would be moved at high speed in a circle using a strong magnetic field. This movement caused the electrons to radiate energy, and the length of the radio waves they produced was then controlled by the size and spacing of the cavities.
Once the essential premise of the device had been proven, it took several more months of intensive practical work to ready the cavity magnetron for its all-important trial. Due to the intense heat that the magnetron produced, it was fitted with a series of copper pipes through which cold water was pumped to regulate its temperature. The entire structure also needed to be encased in copper and glass, as well as the ubiquitous sealing wax, to ensure it remained airtight when the large vacuum pumps were attached to evacuate the air from within the magnetron.
It presented a cumbersome, sprawling apparatus when it was pieced together in Birmingham’s main physics laboratory, where it filled an entire workbench and sections of the surrounding floor space. But on the morning of 21 February 1940, the first cavity magnetron blazed into life as its heated discharge shimmered with a triumphant neon-blue glow. Such was the output of energy, cigarettes that jubilant research staff poked at the unit’s antenna were lit almost instantaneously.
Oliphant instructed that the waves it emitted be used to illuminate a series of car headlights, to accurately gauge the power output. Then, as lamps of increasingly higher luminescence burned out and were eventually replaced by more resilient fluorescent tubes, it was assessed to be pumping out around 400 watts: ten times the output of any previous magnetron.
The other essential question – whether the wavelength would meet the Admiralty’s specifications – was tested at the laboratory the following morning. The measurement of 9.8 centimetres fell comfortably within the margin of error for the ten centimetres the Admiralty had prescribed.
Subsequent engineering input from Randall’s former employer, the huge General Electric Company plant at Wembley, then rendered the device more securely airtight, which meant the bulky vacuum pumps could be dispensed with. General Electric also designed sleek fins that allowed the unit to be cooled by airflow rather than constant water supply.
It was ‘mission almost accomplished’. All that remained was for the unit, streamlined to be not much bigger than a modern-day, handheld hairdryer, to undergo field testing. Oliphant himself delivered the priceless cargo, perched on the seat of his much-travelled Morris, to the radar development station secreted on the clifftop at St Alban’s Head, near Swanage on Dorset’s coast. From that windswept eyrie, echoes were successfully bounced off gulls flying overhead, and off a man on a bicycle several kilometres down the road. It was also successfully aimed at targets of more strategic interest, including ships in the English Channel and, vitally, a submarine periscope that had broken the waterline out at sea.
There were, of course, other obstacles to overcome before the end goal could be realised and the device installed in fighter cockpits. Further refinements were made to the cavity magnetron in the Birmingham laboratories, and in those First World War wooden huts that Oliphant had cannily appropriated to house the radar project’s pre-production work. Other modifications included measures to ensure consistent energy output, as well as the manufacture of units with a range of power capacities. The biggest of them was a fifty-kilowatt version, which produced more than 100 times the energy of Randall and Boot’s original model.
British pilots’ dream of being able to detect and deter enemy aircraft they were unable to hear or see now appeared near to reality.
* * *
The fact that a cavity magnetron that met the Admiralty’s ambitious demand had been designed and delivered within virtually six months of ceaseless work spoke volumes for Oliphant’s stewardship, and the acumen and inexhaustibility of the team he had pulled together.
Yet the professor also believed that his essential role in such important work should grant him a measure of immunity from security provisions that he viewed as unwieldy and unnecessary in the pursuit of scientific outcomes. It was a view sternly at odds with that of the military brass who had commissioned the project, and for whom Oliphant was effectively working.
Throughout the First War, Ernest Rutherford had held strongly to the idealistic view that ‘science is international, and long may it remain so’.6 Oliphant wholeheartedly shared his late mentor’s philosophy that the pursuit of research should benefit all, not simply those with a commercial or ideological interest
Fortified by Rutherford’s stories about the different standards that applied to those in uniform and to their colleagues in laboratory coats, Oliphant had honed a healthy disregard for the military’s superiority complex. He had sent ill-advised correspondence to Lawrence even before war was declared, and throughout the war years he would indignantly challenge, or often simply ignore, bureaucratic efforts to commandeer scientific discovery for partisan purposes. In his no-nonsense way, he stormed a path through what he considered the absurdities of bureaucratic red tape and overbearing officialdom.
When the British embarked on their exploration of radar in the years before the war, there had been guarded hope that the research might uncover some form of ‘death ray’ that could be fired from the ground to melt an aircraft’s metal skin and thereby neutralise invaders in the sky.
Consequently, the harnessing of microwave radiation brought fears, which soon percolated to the public and which remain in some quarters today, that this unseen force represented the lethal radiation futuristic comic books and sensationalist magazines had warned about. To allay such fallacies when microwave generators were first manufactured in his Birmingham laboratory in 1940, Oliphant voluntarily exposed his head to a sustained bombardment of 8.3-centimetre microwaves. The demonstration continued until perspiration cascaded down his reddened face, thus proving his point that the pulses delivered nothing more sinister than heat.
His practicality also allowed him to circumvent some of the less rigorous security measures invoked during wartime. Throughout the development of the magnetron, Oliphant’s primary role had been to inject ideas and remove obstacles. At one stage, his research team found need for an ingot of cadmium–copper alloy, which offered similar conductivity to pure copper, but was able to withstand more extreme temperatures. Oliphant phoned a known producer of the compound from his Birmingham office, while ‘looking idly out of the window at my car, parked nearby’.
‘Having confirmed that they could supply, the person at the other end asked “what is your priority number?” I had no idea that such numbers existed as we normally obtained all supplies through the Admiralty. But, without hesitation, I read off the number of my car, GOB 1676. The material was delivered promptly, and I never heard anything more about it.’7
As Randall would recall of his ever-present leader and enthusiastic collaborator: ‘Oliphant pushed the needs of the lab without thinking whether it was the most tactful way to do it. It was just part of his personality, there was no malice.’8
Further evidence of his running battle with security was reported at one of the radar project’s secret testing facilities on England’s south coast. One of his colleagues was bail
ed up by a supervising officer there, who moaned: ‘The guards at the gate, and the stock room people, say they can’t cope. There’s a man called Oliphant who keeps coming back and forth through the main gate. He doesn’t have any identity card and he comes in with things marked: ‘Property of the Cavendish’. He leaves [them] here, goes out, takes some of our own property for testing, as he says, yet he won’t give any rhyme or reason. He just laughs it off.’
At which point Oliphant’s colleague pointed out: ‘Look, Sir, this is one of the great physicists of the country. His lab has produced this microwave tube which we’ve told you about but which you haven’t yet seen. It’s on three thousand megacycles . . .’
The superintendent’s jaw dropped; his pupils dilated. ‘What did you say? Three thousand megacycles?’9
When the science colleague confirmed that was the case, and added that the breakthrough was being heralded as the key to quelling the nightly German air raids, Oliphant was allowed to continue breezing in and out of the compound with impunity.
Yet for all its experimental success, Birmingham University’s ground-breaking work brought little initial enthusiasm from the Admiralty’s naval signal school, which only served to reinforce Oliphant’s jaundiced perception of the military and their dismissive attitude towards science.
True to their title, the signal school preferred to communicate by hand-operated Morse keys rather than cable, and when Oliphant received a message bluntly demanding that a magnetron be tailored to a specific frequency, he politely replied that a range of models now existed, designed to fit a variety of purposes. Therefore, if the school could provide more detail as to the role they needed the device to serve, he would ensure that the appropriate version was consigned to them. He was briskly informed that the information would not be forthcoming, as the application planned was ‘top-secret’. To which the professor signalled back in blunt shorthand: ‘no information, no magnetron’.
Oliphant later recalled: ‘Next morning the Captain of the Signal School arrived with several colleagues in uniform. They were most apologetic – arms across shoulders, much “Old Chap” and all of that. They went away with an existing magnetron, quite happy that it would do what they required.’10
There were occasions, however, when Oliphant was forced to concede that due process and security protocols were needed. An unannounced visit, at the height of Birmingham’s magnetron development, by Lord Rothschild, who served as a senior counter-intelligence officer – and would be posthumously accused (without proof) of working as a Soviet operative – brought a sweeping inspection of the department’s facilities, but no clear explanation as to the reason for his attendance.
For twelve hours or so, Oliphant believed His Lordship had failed to find any matters of immediate concern.
‘Next morning, a special courier appeared with a top-secret parcel,’ he later recounted. ‘It contained a magnetron, which Rothschild had pocketed as he went round, and a brief note saying only “Perhaps you should tighten things up a bit!” No dressing down would have been as effective.’11
* * *
Albert Rowe, who would oversee Britain’s radar program before being appointed Vice-Chancellor of Adelaide University, evaluated the cavity magnetron as being ‘of far more importance than the atomic bomb’12 in deciding the Second World War. It was a weapon for which Germany, despite the frightening power and technical audacity of their Luftwaffe, found no match, having based their radar system on the inferior klystron.
The cavity magnetron would go on to become a fixture on every civilian aircraft, as well as in most modern kitchens. The valve that could shoot out pulses of radio energy in ten-centimetre wavelengths and was born as a strategic weapon against imminent invasion is now the high-frequency heart of the microwave oven.
An original version of Randall and Boot’s ground-breaking device is displayed in its ingenious simplicity within a glass case at London’s science museum. But it was never more celebrated than when it arrived, concealed inside a securely locked and closely guarded box, in the United States at the end of summer 1940.
The German offensive that Britain had feared for more than twelve months arrived with a few sporadic sorties in early May of that year, but by August it had intensified to daily and nightly aerial raids on military installations, industrial sites and even residential neighbourhoods. Radar granted the Royal Air Force the advantage of forewarning, but the sheer scale of the onslaught meant the island’s every resource was now directed towards basic survival.
With a land invasion expected at any time, it was certainly beyond Britain’s compromised manufacturing capabilities to produce the cavity magnetron in the volumes that the war demanded. Therefore, barely three months after succeeding Chamberlain as Prime Minister, Winston Churchill agreed that the coveted device, so patriotically forged for the war effort, should be included among an assortment of confidential British military innovations that would be handed over, free of charge and reciprocity, to America. In return, Churchill would ask the United States – whose entry into the war remained more than a year in the future – for its essential financial and industrial aid.
This selfless gesture, or blatant cry for help, led to the Tizard Mission. It was an operation that Vannevar Bush, scientific advisor to President Franklin D. Roosevelt, would pronounce ‘the most famous example of a reverse lend-lease’: a reference to the program under which the United States provided aid and materiel to its allies during the war in return for local supplies and no-cost leases on military bases. It was adjudged ‘reverse lend-lease’ because it was one of the few items of intrinsic military value to flow into the United States in those first desperate years of the conflict.
Henry Tizard travelled to Washington, DC, on 14 August 1940, instructing his radar expert, Edward ‘Taffy’ Bowen, to follow by boat a fortnight later, bearing the treasure chest. In the suitcase-sized, black-lacquered deed box, whose sides had been drilled with holes to ensure it would sink without trace if it had to be hurled overboard, lay Britain’s best secrets. Among them were blueprints for a new turbo jet engine, designs for a variable time fuse that enabled the programmed detonation of explosives, and plans for submarine detection devices as well as self-sealing fuel tanks.
At the bottom of the box, beneath bundles of documents and reels of film portraying the graphic horrors of Germany’s relentless air blitz, rested the cavity magnetron. It would be the dramatic final presentation among Tizard’s gifts of goodwill to his American science counterparts at their meeting in Washington’s Wardman Park Hotel.
The effect when the magnetron was revealed and explained was even more theatrical than planned. The Americans were awestruck. The notion of airborne radar challenged their comprehension, given that their technology, like that of Germany, was built around the low-energy klystron.
James Phinney Baxter III, official historian of the Office of Scientific Research and Development, later proclaimed in his Pulitzer Prize–winning book Scientists Against Time:
The British made a great advance . . . but the greatest of their contributions to radar was the development of the resonant cavity magnetron, a radically new and immensely powerful device which remains the heart of every modern-day radar experiment.
This revolutionary discovery, which we owe to a group of British physicists headed by Professor M.L. Oliphant of Birmingham, was the first tube capable of producing power enough to make radar feasible at wavelengths of less than 50 centimetres. When the members of the Tizard Mission brought one to America in 1940 they carried the most valuable cargo ever brought to our shores.13
By war’s end, almost a million magnetrons had been produced, mostly in the United States and on a much smaller scale in Britain.
* * *
Even before the Tizard Mission had set out for the United States, the need to drastically bolster Britain’s defensive capabilities had become critical. The eight-month ‘Phoney War’ that immediately followed Poland’s fall, during which an anxious world
observed Germany’s simmering inaction with trepidation, had given way to the Nazis’ brutal westward push.
Britain’s vulnerability to a repeat of the aerial blitzkrieg that Hitler had unleashed on Poland meant the nation was set to high alert. Despite Churchill’s defiant rhetoric, measures were being quietly taken lest its defences falter.
When news of France’s capitulation was broadcast to a fearful population in June 1940, Oliphant was in his office and promptly telephoned Rosa at home in Barnt Green.
‘France has fallen, you’ll have to take the children and go and live in Australia,’ he decreed in his authoritative tone.
‘I won’t go,’ Rosa countered, in softly stoic defiance. She had been through a similar conversation a decade earlier, when told she was to remain in Adelaide with Geoffrey to escape Britain’s winter. This time, she half-heartedly asserted that she and the children would not depart without Mark, given the political climate heading into that fraught northern summer as the German threat intensified. All the while she knew, however, that it was not a topic for debate.
Although rural Worcestershire seemed safe from the gathering terror of the Luftwaffe’s strikes, Birmingham’s importance as a heavy manufacturing hub meant it was already in Hitler’s bombsights. With troops massed along Europe’s shoreline from France to Norway, the enemy darkening the skies might also be in the streets at any time.
Within a fortnight of being told she was to leave, Rosa and the children had packed several trunks and were booked passage aboard the Orient liner Orcades. Mark then drove them to Southampton, where they joined the exodus of families headed, they hoped, for safer territories aboard blacked-out passenger vessels. Canada’s University of Toronto had already offered to repatriate wives and children of academic staff from sister institutions in Oxford and Birmingham until it was appropriate for them to return – or so grim that their men folk would be forced to join them.
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