The U.S. developed an aircraft-mounted radiotelephone near the end of the war known as the SCR-68 (Set, Complete, Radio). This DH-4 has one, indicated by the generator on the wheel strut. That generator is a good example of linking a modification to a new capability: voice communication instead of telegraphy. The U.S. Army Signal Corps discovered many problems with it, primarily its inability to communicate beyond three miles. To communicate with the ground-mounted SCR- 67, the observer extended a 300-foot, long wire antenna out the rear of the aircraft. The SCR-68 was one of the first steps towards developing more effective messaging system between pilots and commanders and opened a whole new challenge for signals intelligence (SIGINT).