The Boeing/Sikorsky RAH-66 Comanche was an advanced five-blade armed reconnaissance and attack helicopter designed for the U.S. Army. The RAH-66 program was canceled in 2004 before production started and after nearly $7 billion was spent on the program.
During the early 1980s, the U.S. Army began formulating a requirement for a replacement of its helicopters then in service, resulting in the Light Helicopter Experimental (LHX) program. In 1991, the Boeing-Sikorsky team was chosen to produce prototypes. The Comanche would incorporate stealth technologies, featuring a number of designs previously untried. It was to employ advanced sensors in its reconnaissance role, and was intended to designate targets for the AH-64 Apache. The aircraft was also armed with missiles and rockets to destroy armored vehicles.
The two RAH-66s are now museum exhibits.
Source: Wikipedia, "Boeing/Sikorsky RAH-66 Comanche", available under the CC-BY-SA License.