I was wondering whether this would be better on AH&N (or in the Rotorheads flight manuals thread), but I thought some Rotorheads might like to see these ...
Google has digitized some old US Army operator's manuals held in library collections.
You can download a PDF by clicking the drop-down next to the cog shaped icon (on the right). Google eBooks terms of service apply - they appear on the front page of the downloaded PDF.
OH-6A
Operators Manual: Helicopter, Observation OH-6A. - Google Books
CH-54B
Operators' Manual: Army Model CH-54B Helicopter - Google Books
What a mighty beast!
UH-1H
UH-1H/V Helicopter: Operator's Manual - Google Books
I found a few others e.g. AH-1S, AH-64A, as well as maintenance manuals.