UH-60X Stealth Blackhawk (MHX)
In the 1 May 2011 operation that killed Osama bin Laden, it emerged that the 160th Special Operations Aviation Regiment, which operated the helicopters during the raid, used a highly modified version of the UH-60. Features apparently include a modified tail section with extra blades on the tail rotor and other additions which significantly lowered noise levels from that of conventional UH-60s.
It also had low-observable technology similar to that of F-117 that enabled it to evade Pakistan Air Force radars. The aircraft seemed to include features like special high-tech materials, harsh angles, and flat surfaces, found only on sophisticated stealth jets. This came to light only when one of the helicopters used in the operation crashed and was subsequently destroyed except for its tail section. Low observable versions of the Black Hawk have been studied as far back as the mid-1970s