This is a recording of the rebel yell used by Confederate soldiers in many of the battles. It is nothing like the "Yee Haw" most people associate as the Rebel Yell, it is more of a bark. What I also found interesting is that there wasn't just one Rebel Yell: each regiment had their own variation.
The recording is from a veteran from Northern Virginia. And when I heard it, the little hairs on my neck stood straight up: No wonder Union soldiers turned and ran.
http://www.youtube.com/watch?v=ssLMroT2euQ