EARLY HISTORY OF RADAR — PAGE 317 



radar, it fails to meet the radar criteria on several counts. The pulses 

 were much too long, being about half a millisecond. This would 

 blank out the first 50 miles of range. The ratio of pulse spacing to 

 pulse duration was too low, being only four or five, therefore subject 

 to saturation by a very few targets. The receiving equipment was not 

 at the point of transmission, so time of flight of radio pulses to target 

 and back could not be measured in terms of an independent time 

 standard. Only the difference in length of two propagation paths 

 was measured, and direction was not indicated. These deficiencias 

 from the radar viewpoint were imposed by the state of the art in 1925. 

 They detracted nothing from the excellence of the method or the 

 apparatus for probing the ionosphere. In 1930 patent applications 

 were filed by Wolf and Hart for a radio pulse altimeter. The dis- 

 closures were based on the technology of the ionosphere probe, and 

 were therefore subject to some of the same limitations. No develop- 

 ment of radar apparatus resulted from these disclosures. In November 

 1933, Hershberger (U.S. Signal Corps) proposed a method essentially 

 similar to that of Loewy and then did some work on microwave gen- 

 erators in a vain attempt to obtain the power required for useful 

 echoes. In 1936 the French liner Normandie was equipped with a 

 microwave anti-collision device similar to that of Huelsmeyer. 



It is now obvious that contemporary technology contained much 

 that was suggestive of radar. However, none of the art described 

 contained all five elements necessary to radar, and no radar develop- 

 ment resulted from any of it. It is therefore inappropriate to trace 

 the development of radar to any of these proposals or related 

 developments. 



The first incident that led ultimately to radar was the accidental ob- 

 servation by Taylor and Young in September 1922 that a ship in- 

 terrupted some experimental high-frequency radio communication 

 across the Potomac when it intercepted the propagation path between 

 transmitter and receiver. Taylor and Young had for many years been 

 employed by the Navy, and were keenly aware of the problem of 

 screening Naval forces from penetration by other ships in darkness 

 and fog. Though the observation was unrelated to their experiment, 

 the application was obvious to them, and they immediately proposed 

 that high-frequency radio transmitters and receivers be installed on 

 destroyers to detect the passage of other ships between any two de- 

 stroyers in radio contact. Obviously this was not radar. It did not 

 even involve reflection of radio waves, and was in no way related to 

 Marconi's suggestion, as has sometimes been inferred. It is identified 

 with radar here only because Taylor and Young later originated the 

 first radar development project, and this incident started them think- 

 ing in terms of detection of moving objects by radio. 



