DARPA’s history and drive appears to date back to the 1970's when they saw many vulnerabilities of U.S. aircraft and their on-board equipment was easy in terms of detection and attack by potential enemies, who were deploying new SAM'S (surface-to-air missiles) technology , These systems integrated radar-guided and air-launched radar-guided missiles, all networked with early warning, acquisition, and targeting radars, and coördinated within sophisticated command and control frameworks.
Because of such threat to security DARPA embarked on a program to develop strategies and technologies for reducing radar detectability,this also included technologies that changed more conventional shapes of aircraft to something much more reductive to radar detection through a combination of shaping (to minimize the number of radar return spikes) but it didn't just stop at that the list goes on with radar absorbent materials; infrared shielding, exhaust cooling and shaping, and enhanced heat dissipation; reduced visual signatures; active signature cancellation; inlet shielding; and windshield coatings.
all this development eventually led to a project named 'HAVE Blue', this was the first practical combat stealth aircraft, after making its first test flight by the end of 1977. The test and refinements continued leading to the realization of of the F-117A stealth fighter, which became operational in October 1983. In the follow-on development, the TACIT Blue aircraft, could operate radar sensors while maintaining its own low radar cross-section. This also inspired development of the B-2 stealth bomber.
Since their inception these stealth aircraft have destroyed key targets in conflicts in Iraq, both in the 1991 'Desert Storm operation' and in 2003 during 'Operation Iraqi Freedom'; in Afghanistan during Operation Enduring Freedom in 2001; and in Libya in 2011