Heat, smoke, and that loud "wop-wop" sound make helicopters easy targets on the battlefield. For these reasons, helicopters make the unlikeliest candidates for stealth technology. But during the 1990s and early 2000s, Boeing-Sikorsky challenged that notion with the RAH-66 Comanche helicopter.
The Light Helicopter Experimental program is the brainchild of the U.S. Army. It charged Boeing-Sikorsky with developing armed reconnaissance and attack helicopters. The result incorporated stealth technologies that minimized radar and human detection.
Two prototypes were built and tested but the project was ultimately canceled in 2004.