Automation's Finest Hour: Bell Labs and Automatic Control in World War II

h a t does a telephone have to do with an anti-aircraft gun? In World War 11, the two became intimately connected, as telephone engineering reshaped the technology for shooting down airplanes. In 1945, Warren Weaver, former head of research on control systems at the National Defense Research Committee (NDRC), explained the unlikely role of telephone engineering in solving the “antiaircraft problem.” At,first thought it may seem curious that it was a Bell Telephone Laboratories group which came forward with new ideas and techniques to apply to the AA [anti-aircraft1 problems. But for two reasons this was natural. First, this group not only had long and highly expert experience with a wide variety of electrical techniques. Second, there are surprisingly close and valid analogies between the fire control prediction problem and certain basic problems in communications engineering [l]. During World War 11, engineers at Bell Telephone Laboratories applied their expertise in communications to the control of machinery. They designed and built a gun director that employed electronic circuits and servomechanisms to perform calculations. This device replaced earlier mechanical directors and, when integrated with new microwave radars, proved particularly successful at shooting down the V-1 “buzz bombs”-early cruise missiles. By applying theories of feedback amplifiers to servomechanisms and automatic control systems, Bell Labs engineers merged electronic messaging with technological power. This article outlines the contributions of Bell Telephone Laboratories to “system engineering” of anti-aircraft guns. Detailing the labs’ more significant projects illustrates how techniques originally developed for the telephone system acquired utility and conceptual power when applied to military problems. The products of this research, tempered by war, were then adapted to general problems in electronics, communications, and information systems. Research into control systems, which addressed computing, noise and prediction, and communications theory, shaped today’s information society as much as did the digital computer itself. By 1940, more than a decade of development had defined the basic layout of an “anti-aircraft system.” Optical input devices (rangefinders and tracking telescopes) supplied the range, bearing, and elevation of the target . As the war progressed, radar took over these functions, at first just for rangefinding and later for target tracking. A central computer or “gun director” integrated these data with settings for wind, terrain, and predetermined ballistics, which depended on the particular gun and shell. The director predicted the future location of the target based on its speed and direction and calculated as output the azimuth and elevation for aiming the guns, as well as a fuze setting (the time after firing when the shell would explode). These data were transmitted to the guns, which pointed automatically with hydraulic power controls or manually with “follow-the-pointer’’ indicators. Still, the existing solutions used mechanical calculations, which were inadequate, especially as the advent of radar and advances in aircraft technology stressed system performance to its limit. Meanwhile, BTL initiated its own gun director project independent of the earlier