Glide Path

by Arthur C. Clarke

  The train was already waiting when he paid off the antique taxi. There was no one else traveling first class, so he had the whole compartment to himself. That was fine; at this time in the morning he did not feel at all sociable, and with any luck he might be able to catch up on some lost sleep.

  London was three hours away, assuming that he arrived on time. Even if he did not, it would scarcely matter; he had four hours to wait between trains, and the railroad would really have to exert itself to make him miss the connection. But four hours was an annoyingly useless sort of interval; when he’d switched from Liverpool Street to Paddington, and had a snack at some cafe, there’d be no time to go anywhere or do anything. “Gone With the Wind” was out of the question, and there was nothing else that he really wanted to see. He thought of revisiting “Fantasia,” still running at Studio One, but he’d seen it for the second time only a few months ago, and those cherubs and centaurs were beginning to pall.

  Alan was confronted with an old problem, and did not know London well enough to solve it. He had never visited the city until the war; for the first two decades of his life it had been remote, vast, and mysterious. It was no longer remote, but its vastness and mystery remained. Nor would they ever be dispelled, for as long as he lived he would remember that magic moment (could it have been only two years ago?) when he had crested the rise of the hills and been confronted by a London no man had ever seen before, or would ever see again.

  With thirty boisterous companions he had been driven down from the training camp where they had been fitted out with their new uniforms, taught how to march, when to salute, and how to behave without disgracing the Royal Air Force. The weeding-out process had already taken place; now they were on their way to learn a trade—that of wireless mechanic. They were also on the way to London, and the fact that the Luftwaffe had an identical goal did not dampen their enthusiasm in the least. The RAF bus that was carrying them reverberated with the bawdy songs they had acquired with their basic training.

  The songs and the laughter ebbed suddenly into silence. The bus was no longer climbing, but had topped the hills and was now coasting down the gentle slope that stretched for miles ahead of them, down into the valley of the Thames. Still far off, yet spanning half the horizon, London was catching the last light of the day.

  But no one had eyes for the city. Floating a mile or more above it were scores—no, hundreds—of brilliant silver teardrops, like a fleet of strange ships at anchor upon the surface of some invisible sea. Though Alan had seen barrage balloons often enough in the past, they had always been in small clusters around some isolated target; he had never imagined the armada that floated above London, and which now transformed the city into a scene from another world.

  The sunlight glancing from the acres of aluminized fabric made the ungainly gas bags look like drops of mercury, almost blindingly brilliant against the darkening sky. It was an unforgettable sight, but even as he admired it, Alan wondered how much protection this airborne shield really provided. In several places, thin columns of smoke were still rising from fires left by the last raid; with a slight sinking feeling, Alan—who had never yet heard a bomb drop in anger—reminded himself that for the next ten weeks he would be living in the middle of the world’s number—one target.

  They were lucky; the Blitz was not yet over, but it had spent its force. Apart from the blackout and the restrictions that now seemed part of life, one could even forget that London was a city at war. The thirty Aircraftsmen Class II (Under Training) who made up Alan’s course were billeted in an infant’s school in the East End, whose pupils had long ago been evacuated into the unfamiliar countryside. Classrooms had been packed with beds and turned into dormitories; there was much ribald mirth about the tiny toilets, but they had to suffice. Discipline was minimal, being enforced by a plump and friendly Sergeant and a remote Pilot Officer who emerged once a day when all the Courses were on parade, and had never been known to reprimand anyone for anything.

  On the whole, it had been a happy time; they had no responsibilities and no worries. At 8:00 A.M. the squads were lined up in the playground, briefly inspected, and marched along the Mile End Road—to the great inconvenience of traffic—until they reached the Thomas Coram Technical Institute, where for six hours a day they were introduced to the fundamentals of radio.

  No—“introduced” was too mild and gentle a word. It had been a high-pressure course designed to pump brains of average intelligence full of electronics in the minimum period of time. Within a few weeks, boys who had previously been unable to change a burned-out fuse were building radios and using cathode-ray oscillographs.

  Alan had expected to find the course easy; after all, had he not been repairing radio sets for a living ever since he left school? He had soon discovered his mistake.

  The empirical trial-and-error skill he had acquired while working in Mr. Morris’s shop (RADIO AND TELEVISION A SPECIALITY, the sign said, though no television set had ever been seen within a hundred miles) was valuable, but totally inadequate for this job. Alan quickly realized that though he could repair a radio, he had never really understood how it worked. His grammar-school physics had stopped short at alternating currents, and had barely hinted at the existence of the electron. As for his mathematics—the less said about that, the better. Alan could still remember the horrified amazement with which he had first encountered the square root of minus one.

  Yet he had made the grade; and now, only two years later, he was an officer, while most of his classmates were corporals or sergeants. He was still not quite certain how it had happened; when he remembered the grim-faced inquisitors of the commissioning board that had interviewed him at Adastral House, it seemed something of a miracle.

  But the ways of the Air Ministry were beyond mortal understanding; and so were those of Group Headquarters. In a few hours he would know what they wanted of him, and meanwhile there was no point in worrying about matters outside his immediate control.

  While the train made its leisurely journey to London, no duties or responsibilities could touch him, and there was nothing that he could do about them even if he wished. He was beyond the reach of the world.

  3

  Originally, 61 Group Headquarters had been built as a country seat by some Victorian merchant prince; its size, impeccable bad taste, and brilliantly contrived inconvenience had made it an irresistible target for the Royal Air Force, which had promptly requisitioned it on the outbreak of war. The current owners, it was rumored, now occupied one of the numerous lodges scattered around the estate—the smallest of which would have accommodated a normal-sized twentieth-century family.

  Wing Commander Stevens’s office, which had once been the third nursery, commanded a fine view of the gardens surrounding the house. To be brutally accurate, it provided an excellent view of where the gardens had been. At the moment it showed a series of prefabricated wooden huts accommodating stores and clerical staff, and an expanse of badly beat-up lawn that was used as a parking place in good weather. In winter it was known as the Slough of Despond and was impassable to all except amphibious vehicles.

  Despite Alan’s fears, the interview had been pleasant enough; indeed, the wingco seemed positively friendly.

  “We need someone,” he said, “for a rather unusual job—someone who picks up new ideas quickly and can put them across to others. Someone who has practical experience, yet can lecture in the classroom. Do you think you qualify?”

  “I really don’t know, sir,” said Alan cautiously. He was still very much on guard, not wishing to show any enthusiasm until he knew what all this was about. One of the first rules he had learned in the Air Force was “Never volunteer for anything.” Like most rules, it sometimes had to be broken, but it had served him well in the past.

  “You spent eight months as a lecturer at No. 7 Radio School, and the Chief Instructor has given you a very high recommendation.”

  “He has, sir?” said Alan, genuinely surprised. It was true that he h
ad enjoyed teaching, and getting down to the fundamentals of new equipment; but it had not really occurred to him that he was good at it. Anyway, he was by no means sure that he wanted to go back to school, with its parades and discipline, after the easygoing life of an operational radar station. By this time, he had practically forgotten how to give a word of command; when he addressed one of his men, he was much more likely to say “Pass the soldering iron, Joe” than “LAC Jones! On the double!”

  The Wing Commander continued to leaf through the dossier on which Alan could see his name and number tantalizingly displayed. He would give a good deal to see what was inside that file, but of course he never would. At least he could now be fairly sure that the electric-shaver incident was not recorded there, and that was a considerable relief.

  Abruptly, W/Cdr. Stevens started to fire a series of technical questions at him. They were all about ten-centimeter radar: how do you tune a klystron; what is the principle of the cavity magnetron; what advantage have wave guides got over transmission lines? It was elementary stuff, and he had no difficulty in dealing with it. At last the Wing Commander seemed satisfied; he closed Alan’s personal file and dropped it decisively in his out-tray.

  “I’m posting you,” he said, “to a Coastal Command airfield in Cornwall, not far from Land’s End. You’ll be joining a very small but very important unit; at the moment it has just one officer, Flight Lieutenant Basil Deveraux, who is attached to a team of civilian scientists. You are to assist him, and if everything works as we hope, then RAF personnel will take over from the scientists and the unit will grow rapidly. That’s all I can tell you; the whole thing is even more secret than ordinary radar, and I can promise that you’ll find it interesting. Ops 4a—second door on the left—will have your travel documents. Good luck!”

  And that was all he saw of 61 Signals Group HQ. Fifteen minutes later, a van picked him up at what had once been the tradesmen’s entrance, and dumped him back at the railway station. Flying Officer Alan Bishop, after two and a half years in the RAF, was now actually on his way to an airfield.

  He was used to these sudden changes of status, but this was the most unexpected yet. When he looked back upon his service life, it appeared to be divided into distinct and almost unconnected strata, like the rock layers pictured in geology books. When you were in one layer, you could not imagine any other existence. Then, suddenly, you were in another—and what lay behind you in time was already dead and fossilized.

  The earliest, or Eocene, layer of his RAF career was already gone almost beyond recall; he even had to think hard to remember the name of the place where it had started. Southbridge—of course! That was where he had said good-by to his civilian clothes, and drawn his first uniform from Stores. (It had fitted very well, too, despite all the jokes, but it was several days before he could stop his cap from falling off every time he saluted.)

  At Southbridge he had been given the number whose last three figures he would remember all his life, for it had been branded into his mind at scores of Pay Parades. When the money was counted out and his name was called, he would step forth from the ranks and reply smartly: “Sir! 727!” Then he would collect his pay, salute, and merge once more into the sea of blue. Being so near the beginning of the alphabet was a great advantage. You never had to wait long for anything, whether it was pay or punishment. The poor W’s and Y’s were sometimes kept in suspense for hours.

  It was at Southbridge that he had learned to drill, and had discovered, to his great surprise, that he enjoyed it. He felt a sense both of solidarity and of achievement when he marched in formation with his fellow airmen, tracing precise geometrical patterns on the parade ground—though according to the Drill Sergeant a flotilla of drunken jellyfish would have done better. He had also discovered—and this was another surprise—that noncommissioned officers were quite human off duty, and not averse to borrowing money from innocent recruits.

  Yes, he had learned a lot at Southbridge, though he had been stationed there for little more than two weeks. It had been the dividing line between two worlds, for once you had put on uniform you were never quite the same again. You had exchanged the freedom and indiscipline of Civvy Street for a planned and regulated existence, in which the very clothes you wore and the way you walked were subject to rules. Even your sex life, according to the widely believed rumor, was suppressed by the Medical Officer, via the medium of bromides in the tea. Not until Alan became an officer himself, and had to inspect the cookhouse as part of his duties, was this ghost laid to rest in his own mind.

  The rabble that had entered Southbridge emerged as fledgling airmen, already steeped in service lore and, in most cases, feeling some pride in their uniform. But at this stage they were good for nothing but sweeping floors, cleaning latrines, and peeling potatoes; they had yet to master a trade, and must now learn the multitudinous skills that were required to fight an aerial war.

  Hence the Thomas Coram Technical Institute, and a hundred similar establishments. Alan had been lucky to receive his basic wireless training in the heart of London, even though it was a London of sandbags and blackouts and air-raid sirens. He had not been quite so fortunate on the next stage of his electronic saga.

  High, cold, and windy on the Wiltshire moors, No. 7 Radio School had been Alan’s university and, later, his home. It was a dismal prospect of barrack huts, parade grounds, and wooden radio towers, yet he had grown to love it. For it was here that he had said good-by to the simple, old-fashioned world of “wireless” and had come for the first time face to face with the unsuspected marvels of radar. Here he had also been introduced to Security.

  It was exciting to feel that every word and drawing in your notebooks was so secret that not a scrap of paper could be taken out of the classroom. The Radio School was a closely guarded enclave set in a remote corner of the camp, surrounded by barbed wire and service policemen. At the beginning of the day the trainees would assemble on the parade ground in the main camp, and would then march almost a mile to their classrooms. When they arrived, the safes would be unlocked and their individually numbered notebooks issued to them; at the end of the day, the books would be collected again. On the rare occasions when one was lost, the whole school was turned upside down until it was discovered.

  Alan had vivid memories of his first radar instructor—a thin, soft-spoken Canadian with a fine gift for sarcasm. Sergeant Lebrun had been a schoolteacher in civilian life and never had any need to fall back upon his three stripes to enforce discipline. His tongue was quite sufficient, and like all good teachers he appeared to have eyes in the back of his head.

  Sergeant Lebrun had smiled with obvious relish at the thirty expectant faces staring back at him, on that first morning in class. “I’ve a surprise for you,” he said. “You think you’ve come here to learn about wireless; some of you may even imagine you know it already. Well, we don’t teach wireless here. We teach RDF—Radio Direction Finding—and even that isn’t what you might suppose.

  “RDF is a means of locating aircraft by radio waves; another name for it is Radiolocation. It’s one of the best-kept secrets of the war, and it’s got to stay that way. That’s why you’re not allowed to take your notebooks over to the main camp, and if you’re ever heard talking about your work here, you’ll be in real trouble. Understand?”

  Course 47 understood.

  “The principle’s very simple. RDF works by sending out a short, sudden radio pulse, and then detecting the echo when it comes back. We have RDF sets here that can spot aircraft two hundred miles away, and can pinpoint them on a map to within a fraction of a mile. That’s how the Battle of Britain was won… with a little help from Fighter Command, of course.”

  No one laughed. The Sergeant’s face did not encourage it.

  “And RDF can do better than that. It can count the number of aircraft in a formation, and tell how high they are flying. It works just as well by day or by night, in rain or in fog, so Jerry can no longer rely on the English weather for protectio
n.”

  A nervous titter started from the back of the room and spread swiftly across the class. Sergeant Lebrun seemed neither pleased nor annoyed—merely a little surprised.

  “If we want to measure distances by radio,” he continued, “there’s one slight problem. Radio waves travel at the speed of light, and that’s the fastest thing in the universe.” He turned to the blackboard and wrote on it, in large, clear figures:

  186,240

  “This is how many miles a radio wave travels in a single second—more than seven times around the world. So we’ve got to be pretty slick to catch an echo from an aircraft only a few miles away. This is how we do it…”

  He turned once more to the blackboard, and began to sketch, while behind him thirty Secret Notebooks lost their blank virginity.

  An hour and several pages later, Alan laid down his pen with a sigh of relief. He was suffering not only from writer’s cramp, but from mental indigestion. Sergeant Lebrun had not, however, quite finished with Course 47.

  “Before you go to Practical class, I’ve an announcement that may interest some of you. There’s a gramophone recital tonight at 1700 in Hut 10b. The program will consist of Beethoven’s “Pastoral” Symphony and Sibelius’ Symphony No. 2. Flight Lieutenant Horsley will give an analysis of the Beethoven. Class dismissed.”

  That was typical, Alan soon discovered, of Gatesbury. The place was an absolute hotbed of culture. Despite the pressure of work, staff and trainees found time to run camp newspapers, music-appreciation classes, debating societies, and even a small symphony orchestra. No airman who entered No. 7 Radio School had a chance of leaving it again if he was a good performer on a musical instrument. He might fail dismally as a radar mechanic; no matter, if he could play the violin.