LITMIR.BIZ

       THE FIRST PREAMBLE

      Arthur C. Clarke says:

      The incidents at Pearl Harbor lay in the future and the United States was still at peace when a British warship steamed into Nantucket with what was later called “the most valuable cargo ever to reach American shores.” It was not very impressive, a metal cylinder about an inch high, fitted with connections and cooling fins. It could easily be carried in one hand. Yet this small object had a strong claim to being responsible for winning the war in Europe and Asia—though it did take the atom bomb to finish the last of the Axis powers off.

      That just-invented object was the cavity magnetron.

      The magnetron was not in principle a new idea. For some time it had been known that a powerful magnetic field could keep electrons racing in tight circles, thus generating radio waves. However, this fact remained little more than a laboratory curiosity until it was realized that those radio waves could be used for a military purpose.

      When it had such a military use, it was called radar.

      When the American scientists working at the Massachusetts Institute of Technology received that first device, they subjected it to many tests. They were surprised to find that the magnetron’s power output was so great that none of their laboratory instruments could measure it. A little later, powering the giant antennae that had quickly been erected along the Channel coast, that British radar did a fine job of spotting the Luftwaffe’s myriad warplanes as they formed up to attack England. Indeed, radar was responsible, more than any other one thing, for allowing the Royal Air Force to win the Battle of Britain.

      It was soon realized that radar could be used not only to detect enemy aircraft in the sky, but to make electronic maps of the ground over which a plane was flying. That meant that, even in total darkness or complete overcast, the land below could be imaged in recognizable shape on a cathode-ray tube, thus helping navigation—and bombing missions. And as soon as the magnetron was available at MIT, a team headed by future Nobel Laureate Luis Alvarez asked the next question: “Can’t we use radar to land aircraft safely, as well as to shoot them down?”

      So began GCA, or ground-controlled approach, the landing of aircraft in bad weather using precision approach radar.

      The experimental Mark 1 GCA used two separate radars, one working at ten centimeters to locate the plane’s direction in azimuth, and the other—the world’s first three-centimeter radar—to measure height above ground. An operator

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