Someone who knows, points out:

One point worth clarifying from the initial reports I have seen – the UH-60 Blackhawk is not an attack helicopter, it is a untility helicopter. It is primarily used to transport troops and supplies, though it does have other uses. The Army actually ‘codes’ the nomenclature of its helicopters. UH-## are utility helicopters, AH-## are attack heilcopters (i.e. AH-64D Apache), CH-## are cargo helicopters (i.e. CH-47 Chinook), OH-## are observation helicopters (i.e. OH-58D Kiowa), and MH-## are modified versions of the basic helicopter.