2 BELL SYSTEM TECHNICAL JOURNAL 



the ground forces' problems of aircraft warning and searchlight control. 

 At the same time intensive work was being pursued at the Naval Research 

 Laboratory at Anacostia, D. C. under the direction of Dr. A. H. Taylor, 

 Dr. R. M. Page and Mr. L. C. Young. Their work was directed primarily 

 toward developing radar equipment that would be useful aboard ship, and 

 it was from them and from the engineers of the Na\^ Department that the 

 principal inspiration and guidance for the work described in this paper were 

 obtained. 



The first military application in which radar equipment proved its use- 

 fulness was in the detection of approaching aircraft. For this kind of 

 apphcation the radar is not required to locate the approaching planes with 

 very great accuracy and the experimental radars of 1938 and 1939 per- 

 formed this function in quite a useful way. The fact that the first appli- 

 cation of radar was a strictly defensive one may account in part for the 

 great interest and support given radar work in England and in this countr}^, 

 while apparently much less radar work was done before the war by the 

 scientists of Germany and Japan. Thus, when radar later became a power- 

 ful and versatile aid to offense, the enemy nations found themselves years 

 behind in development. 



Very early in their work the men of the Naval Research Laboratory 

 recognized the potential ability of radar to help solve the fire-control prob- 

 lem. Since this problem determined the design of the radar systems to be 

 described later in this paper a brief general discussion of fire control is given 

 here. The term fre control refers broadly to the means b}- which a gun or 

 other weapon is aimed and fused so that, when fired, the projectile will hit 

 or burst near the intended target. A fire-control system includes two 

 major parts: first, a locating device for determining the present position of 

 the target; and second, a computing device which analyzes the present 

 position data, computes the target's course and speed, and the position the 

 target will occupy at the future time when the projectile arrives at that 

 point, and finally furnishes the correct aiming and fusing information to 

 the guns. A modern fire-control system does these things in a continuous 

 manner so the guns remain correctly aimed and can be fired at any time 

 during the engagement. 



Before the war the present position of the target was ordinarily de- 

 termined by optical instruments. Operators tracked the target by con- 

 trolling their telescopes in such a way that the target remained on the 

 crosshairs in their eyepieces. Thus the azimuth and elevation angles 

 were found. Another operator measured the range to the target with an 

 optical range finder, or indirectly estimated range from the angular extent 

 of the target and its estimated size. 



The accuracy of this optical system in determining azimuth and elevation 



