SCR - 68 The SCR - 68 ( SCR was a military term meaning Set , Complete , Radio ) was a military radiotelephone used by the US Army Signal Corps as an aircraft radio in the waning months of World War I . Due to its many problems , primarily its inability to communicate with other radios , like its ground component the SCR - 67 or the larger truck mounted SCR - 108 , over large distances , the SCR - 68 quickly became obsolete . Nonetheless , the SCR - 68 was one of the first steps towards developing more effective messaging between pilots and commanders , even beyond military usage . Capabilities . The SCR - 68 had a few distinct characteristics that separated the SCR - 68 from other types of radio . The SCR - 68 operated at 750 kHz ( 400 meter wavelength ) , using a long wire antenna reeled out behind the aircraft . It could receive and transmit messages over a maximum range of eighteen miles . The artillery observer ( navigator ) managed the SCR - 68 , receiving and relaying messages for the pilot . During World War I , most planes were two - person open - cockpit aircraft . Instead of communicating between themselves in the air , the pilot and the observer sent messages through the SCR - 68 where the headphones would eliminate most outside noises . Like a private telephone line , the pilot and observer could communicate with each other ; however , this action prevented the SCR - 68 from receiving any transmissions . Problems . Advancements with the SCR - 68 were marred by its flaws . Military tests by British soldiers reported the difficulty of getting the proper balance with the oscillating and control values . The SCR - 68 range was reliable within a five mile radius , a serious issue when the airplane needed to travel long distances . Another issue with the SCR - 68 was the static noise that came from the “ ripples ” in the generator commutation . The noise was faint and was only considered a problem when receiving messages that exceeded 5 miles . It was later found that metal shielding placed around the wiring helped to prevent this problem . Origins . The US Army pushed for better technology to gain an advantage in World War I . The US Army asked private American companies to build a device that would establish better communication between military aircraft and themselves . Western Electric developed the SCR - 68 that met qualifications : the radio was condensed to a size that could fit inside the airplane , simple for an Observer to use in flight , and the antenna would not drastically affect the movements of the aircraft . Another problem in the past included a communication device that eliminated the most disturbances from engine noise ; the SCR - 68 provided that by including a microphone and a sound - proof helmet . By the summer of 1918 , approximately 3 , 000 units were manufactured and distributed to the US Army . Parts . Radio Set . Inside the suitcase - shaped box BC - 11A was the circuit apparatus used for receiving and transmitting messages . The dials were used to control the frequency of the radio . The flip paddle switched the radio from receive to transmit and vice versa . The dimensions of the box were 17 inches by 10 inches by 7 inches and weighed 21 pounds . Intercom . The BC - 10 ( SCR - 57 ) intercom control box for switching between onboard communication and ground communication . Antenna . The A - 21 retractable antenna was located in the rear of the aircraft and was expanded by the air observer while in flight . It could reel out to 300 feet in length , was made out of two copper wires and weighed 19 . 5 pounds . Depending on the amount of antenna allowed behind the airplane , the antenna functioned at a wavelength of 750 kHz . Generator . The GN - 1 wind - powered generator was located on the braces of the landing gear , to gather adequate wind power and not hinder any other parts of the aircraft . The generator , as well as three 22 . 5 volt batteries located in the BC - 11 , provided a plate voltage at 300 volts and a filament voltage at 30 volts . The wind - powered generator was not very efficient , requiring the airplane to travel at fast speeds in order for the generator to work properly . Other . • T - 3 Single button Chest microphones for sending messages • HS - 1 Headphones , to eliminate external sounds