From the published pictures and quick minded people adapting the public information we can easily tell the helicopter destroyed was no regular MH-60. The tail rotor design is very different from the standard H-60. The Nightstalkers helicopter tail encompasses rarely seen design features that are only similar to the canceled RAH-66. The tail rotor is five bladed compared to the standard 4 blade design plus the rotors hub is in a shape never seen before even further to having a rotor cover not featured on any other type of H-60 known. What these design elements are for no one is quite sure, but there are some theories. Obviously the design probably incorporates some type of stealth. It was noted the Pakistani military did not detect the helicopter force. The design elements probably add some type of radar &/or sound stealth. Helicopters are much harder to hide with stealth than aircraft, but the the 160th is considered by many to have the best helicopters pilots in the world. So a combination of low level flying and stealthier helicopter helped insure the raid was successful.
There are some question that this maybe be a completely new helicopter, but I side with that the helicopter is an advance stealth offshoot of the MH-60. The tail design and shape is too similar to probably be a different type of helicopter. I have actually seen a standard MH-60 & it's big brother the MH-47G in person since I used worked at an airport near where the 160th is based in KY so that's one of the reason I am siding with the modified MH-60 side.
Since questions have begun to run wild on the web, plus the wildly available pictures, we may actually see the first manned black aircraft in years go public.
Here are some pictures and links to show the differences and provide some better information.
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