SCR - 268 radar The SCR - 268 ( for " Signal Corps Radio no . 268 " ) was the US Army ' s first radar system . It was developed to provide accurate aiming information and used in gun laying systems and directing searchlights against aircraft . The system was already considered out of date by the end of World War II , having been replaced by the much smaller and more accurate SCR - 584 microwave - based system after the Tizard Mission provided the US with the cavity magnetron . Development . The Signal Corps had been experimenting with some radar concepts as early at the late 1920s , under the direction of Colonel William R . Blair , director of the Signal Corps Laboratories at Fort Monmouth , New Jersey . While most of the Corps ' efforts revolved around infra - red detection systems ( a popular idea at the time ) , as well as a newer generation of sound detectors , they also maintained a small program of research on microwave radars based on the " beat principle " , in which an aircraft would cause two signals to interfere . Low generator efficiency and a lack of ranging capability made these efforts impractical . In 1935 one of Blair ' s recent arrivals , Roger B . Colton , convinced him to send an engineer to investigate the US Navy ' s CXAM radar project . The navy ' s system traced its development from experiments conducted by Albert H . Taylor and Leo C . Young at the United States Naval Research Laboratory in the early 1920s . William D . Hershberger duly went to see what they had , and returned an extremely positive report . They decided to try to find a need for such a unit in order to gain funding , and eventually received a " request " by the Chief of Coast Artillery on February 1 , 1936 for a gunlaying system with a range of 15 , 000 yards through rain , mist , smoke or fog . Gaining the support of James B . Allison , the Chief Signal Officer , they managed to gather a small amount of funding and " stole " some more from other projects . By December 1936 they had a working prototype , which they continued to work on and improve . On May 26 , 1937 they were able to show the prototype in a convincing demonstration . After failing to find their target Martin B - 10 bomber where it was supposed to be , they started " hunting " for it and found it 10 miles off course . The radar fed pointing data to a team operating a searchlight , and when it was turned on the bomber was seen to be centered in the beam . It was later learned that the target had been blown off course , making the demonstration all the more impressive . Development of this system was slowed to some degree when a long range early - warning radar became a higher priority and parts of the prototype were salvaged for the SCR - 270 they were building . Nevertheless the system entered production at Western Electric about the same time as the - 270 in 1939 . The radar entered service in 1940 , and about 3100 were produced by the end of the war . Description . The SCR - 268 antenna system consisted of a number of dipole elements arranged in three groups , each in front of a passive reflector , mounted on a large aimable cross . The cross consisted of a short upright pedestal sitting on top of a large base platform , mounting long cross - arms extending from the midpoint of the upright pedestal . The antenna system was about forty feet wide and ten feet high overall . Both the pedestal and the cross - arm could be rotated around their axis for aiming , in azimuth and altitude respectively . The left side of the cross arm , as seen from the back , contained a set of dipoles that were set to be sensitive in angle , while almost insensitive to elevation . It was arranged six dipoles wide and four dipoles high , each with its own reflector . On the far right side was a similar , but smaller , arrangement rotated 90 degrees in order to be sensitive in elevation and not angle . This portion was two dipoles wide and six dipoles high with corresponding reflectors . Finally in the " middle " of the cross , between the upright pedestal and the elevation antenna , was the broadcasting array which created a circular beam about 10 degrees wide . The three radar operators sat at consoles mounted on the pedestal just below the antenna cross - arm , each with their own oscilloscope display . One controlled the azimuth , another the elevation , and the third the range . Pointing the antenna was controlled by rotating large handwheels , the range being reported by a similar wheel . The accuracy of the antennas themselves was not very high , about 9 - 12 degrees , so simply rotating the antenna and looking for a maximum would not point it very accurately . To help with this the antennas were deliberately designed to have two directions of high sensitivity , or " lobes " . Signals from both lobes were displayed , slightly separated , on the layer ' s displays . By adjusting the antenna until the returns from both were equally strong , accuracies of about one degree were possible . Range information was taken from the elevation array , and worked , as it did for most radars of the era , by triggering the trace on an " A - line " oscilloscope and read against a scale at the bottom . A second blip was also generated by equipment attached to the rangefinder ' s handwheel . By rotating the handwheel until the reference blip overlapped the one returned from the antenna , the timing could be read from the wheel . Range accuracy was about plus or minus 200 yards . The system also included two sets of " repeaters " that sent the directional information to a searchlight , and both the directional and range ( as dialed in on the rangefinder ' s handwheel ) to a gun . The accuracy was not enough for direct gunlaying , but in combination with a searchlight the gun ' s existing optical equipment could " fine tune " the radar ' s guidance . The radar operated at 205 MHz with a PRF of 4098 pulses per second of 6 μS duration , with an inter - pulse time of 240 μS . Radio waves ( light ) travel at about 0 . 093 miles / μS round - trip , so the system had a maximum range ( 240 × 0 . 093 ) . It broadcast about 75 kW of power , which was , in theory , more than enough to offer longer range . The radar was mobile , requiring four prime movers for support . Two towed the radar base and the antennas themselves , another pulled a K - 34 trailer van providing power , and the fourth a van that converted the power to high voltage for the radio equipment . In total , including the trucks , the SCR - 268 weighed 82 , 315 pounds . That the system was mobile at all was more a testament to the US ' s overwhelming industrial might than any quality of the radar itself . The SCR - 268 was not a particularly advanced design by the standards of the era . Early units were technically behind the times in terms of tracking in particular ; while the SCR - 268 was being introduced , the Germans were upgrading the Würzburg radar , first to use lobe switching , and finally to conical scan the next year . These sorts of changes were simply not possible on the SCR - 268 due to its long wavelength , which demanded a non - circular antenna . The only way to " fix " this problem was to move to a microwave radar of their own , an effort that started after the Tizard Mission . This led to the introduction of the SCR - 584 , which fit the entire radar system on a single trailer , added conical scanning , and was generally much more accurate and far easier to operate . SCR - 268s were removed from service almost immediately with the ending of the war . The SCR - 268 was one of the first radar sets to use lobe switching of its receiving antennas as a means to locate AA ( anti - aircraft ) searchlight beams on aircraft . Since it did not lobe - switch its transmitted signal it would be classes as one of the first LORO radars . Surviving examples . There are no known surviving examples of this array .