Larry Knowlton, age 13, of Biloxi, miss., for his question:
WHEN WAS RADAR DEVELOPED?
Radar is an electronic device that can locate distant objects despite darkness, clouds, rain, fog or snow. Although it didn't become an important military device until World War II, the most important discoveries leading to the development of radar came in the late 18009 and the early 19009.
Four men were contributors to the development of radar, which uses radio waves instead of light waves to "see" great distances. The four were Heinrich Hertz, Guglielmo Marconi, Karl Braun and Lee DeForest.
Hertz discovered radio waves in the 18809 and showed that they could be focused into a beam and be reflected from objects. In the 1890s, Marconi developed the first radio sending equipment. Braun invented a cathode ray oscilloscope in 1897, and in 1907 DeForest invented the radio amplifier tube.
The name radar comes from the phrase "Radio Detection and Ranging." Radar sends out pulses of radio waves in a beam. As the waves strike objects, they are reflected like echoes back to the radar. The reflected waves cause dots of lights called blips to appear on a fluorescent screen similar to a TV screen. By watching the blips, an observer can tell the direction and distance to an object.
Much of the early work in the United States on radar was done by scientists at the Naval Research Laboratory. A.H. Taylor and L.C. Young detected reflections from a boat on the Potomac River in 1922 while studying short wave radio.
Young and L.A. Hyland observed similar reflections from aircraft in 1930. The scientists used a system of continuous radio waves called the beat method. This method did not give the range of an object, but it could detect aircraft 50 miles away.
In 1934, Young proposed using pulses of radio waves, the method most widely used today.
By early 1936 pulse radar with a range of 25 miles had been developed, and by 1938 a pulse radar had tracked an aircraft 100 miles. This kind of radar was installed on 20 warships before the Japanese attacked Pearl Harbor on Dec. 7, 1941.
The Army had two excellent types of radar ready by 1941. An Army radar unit in the Hawaiian Islands detected the Japanese air fleet approaching Pearl Harbor, but thought the blips were caused by American bombers.
During World War II, United States and British radar scientists cooperated closely. Microwaves made it possible to develop narrow beamed, highly accurate radars with small antennas for aircraft, ships and mobile ground stations.
American scientists did much of their radar work at the Radiation Laboratory, located at the Massachusetts Institute of Technology.
During World War II, radar gave the U.S. Navy superiority over Japanese forces in night battles. In the Atlantic, airborne radar enabled the Allies to inflict crippling losses on the German submarine fleet.