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.