Aircraft Detection Prior to the Invention of Radar

Beginning in the middle of the 1930s, engineering labs in the U.S. and Europe were experimenting with radar systems. Early radars did not have the slick plan position indicator (PPI) displays that modern systems use for plotting target movement for indication of azimuth (direction) and range (distance). Instead, oscilloscopes showed radar returns as amplitude blips along a time base that represented range. Azimuth was determined by where the operator pointed the antenna (rotating versions came later). Since radar cross section stealth technology had not been invented yet, the amplitude of the signal was useful a measure of the size of the target.

Prior to the invention of radar (RAdio Detection And Ranging), other means were needed to detect approaching aircraft during times of war. Human spotters were often posted in open fields, tall building rooftops, shorelines, and hills in order to provide a measure of warning against approaching enemy aircraft (acoustic defense). Effectiveness was dependent on many parameters like quality of eyesight, hearing and alertness of the observers, atmosphere transparency (visibility), light level, aircraft size, configuration, color and noise level, etc. Even under ideal conditions detected aircraft would be no more than a few minutes away from the observer, so that did not leave a lot of time to prepare a response. Observer networks were set up as far in advance of key targets as possible through a radio relay network, but it left a lot to be desired.

That's where the strange, often Dr. Seuss-looking listening devices shown below were designed and employed to aid the observers. These photos are all over the Internet, so I do not know their origins. I will be glad to credit the true owner(s) if contacted, and will provide a hyperlink to the originals. Thanks to Bob D. for letting me know about them.

Compliments of Dr. Seuss	Didn't I see an ad for this in the back of Popular Science?	An alt-az mount - impressive!
Modified cheerleader megaphones	Also useful for listening to avian mating rituals	OK, this one has to be a joke
Dr. Seuss again	This concept was later used as an inspiration for the Ferris wheel	Achtung! Wir hören können alles, was sie sagen.

The douglas-self.com web page link was sent to me after posting these pictures. It has more information on these pictures. You'll probably enjoy perusing some of the other topics he has as well.

Here is a page on early radar development.

See the Homemade Plane Detector article from the May 1942 Popular Science magazine.