Academic Reading — Test 32

Reading passage

In the years before the Second World War, the British government grew increasingly anxious about the threat posed by enemy bombers. The widespread belief among military planners was that aircraft would always be able to penetrate a nation's defences, and that cities could be devastated before any warning was given. This fear prompted officials to search for a method of detecting approaching aircraft while they were still far away, ideally beyond the range of human sight and hearing. Earlier attempts had relied on enormous concrete structures known as acoustic mirrors, which were designed to gather and focus the sound of distant engines. These devices proved disappointing, however, because they could be confused by ordinary noises and gave only a few minutes of warning. A decisive change came in 1935, when the physicist Robert Watson-Watt was asked to assess a rather fanciful proposal for a "death ray" that might destroy aircraft using radio waves. Watson-Watt and his assistant calculated that the energy required to harm a pilot was far too great to be practical. Yet the same calculations revealed something more valuable: radio waves striking an aircraft would be reflected back, and those faint echoes could be detected and measured. In a celebrated demonstration near Daventry in February of that year, a passing bomber was tracked using signals from a nearby broadcasting transmitter. The principle of detecting aircraft by radio echo had been established, and the work was given high priority and considerable secrecy. Over the next few years, a network of tall transmitting and receiving towers was constructed along the southern and eastern coasts of Britain. This system became known as Chain Home. The stations sent out pulses of radio energy and listened for the reflections returning from any aircraft in the area. By measuring the time taken for an echo to return, operators could estimate how far away a target lay; by comparing the strength of signals received on different aerials, they could work out its direction. The information was far from perfect, and skilled operators were needed to interpret the flickering traces on their screens, but the system could detect aircraft well over a hundred kilometres away. One limitation was that Chain Home could not easily detect aircraft flying at low altitude, so a complementary system called Chain Home Low was later added to cover that gap. The technology alone, however, would not have been enough. What made British radar so effective during the Battle of Britain in 1940 was the way the information it produced was gathered, checked and distributed. Reports from the radar stations, together with sightings from the Observer Corps once aircraft had crossed the coast, were telephoned to a central headquarters. There the data were combined into a single, constantly updated picture of the air situation, which allowed commanders to direct fighter squadrons to the right place at the right time. This arrangement, sometimes called the Dowding System after the commander who oversaw it, meant that defending aircraft were no longer wasted on fruitless patrols. Instead, they could be held on the ground and sent up only when an attack was confirmed, conserving both fuel and the energy of exhausted pilots. Radar continued to develop rapidly throughout the war. A major breakthrough was the invention of the cavity magnetron, a compact device capable of generating powerful radio waves at much shorter wavelengths than before. Shorter wavelengths allowed for smaller aerials and far sharper detection, which made it possible to build radar sets small enough to fit inside aircraft and ships. Airborne radar helped night-fighters to locate enemy bombers in darkness, while sets carried by patrol aircraft and warships became a serious threat to submarines operating in the Atlantic. The magnetron was considered so important that it was shared with the United States, where it was manufactured in large numbers and developed further. It would be misleading to suggest that radar alone won the war, and historians are careful not to overstate its role. Many factors, including the courage of aircrews, industrial output and intelligence work, contributed to the eventual outcome. Nevertheless, radar transformed the nature of aerial warfare and gave Britain a crucial advantage at a moment of great danger. Perhaps its most important legacy was the demonstration that scientists, engineers and the armed forces could work closely together to turn an abstract physical principle into a practical instrument within a remarkably short period of time. The wartime experience also laid the foundations for the many peacetime uses of radar that followed, from air traffic control to weather forecasting.