A question on Jeopardy last evening made me look up the Gatling gun on Wikipedia. This got me interested in the weapons used during the "Uncivil" War. According to the web, prior to the war, most infantry tactics were based on the use of the smoothbore musket.
Because this gun had limited range and accuracy, what I read said that firing lines further away than 100 yards didn't do much damage on each other, so the troops would mass together and make a run for it when attacking. If there were enough of them and they ran fast enough, the defensive line could not react quickly enough to hurt them.
The Civil War musket however, was rifled, which made an enormous difference. It was still a muzzle-loader, but had much more accuracy and a far longer range than the old smoothbore and it completely changed the conditions under which soldiers fought. The massed charge of Napoleonic tradition was now hopelessly out of date.
The hideous casualty list of Civil War battles was directly related to the fact that soldiers were fighting with rifles but were using tactics suited to smoothbores. It took the generals a long time to learn that a new approach was needed. Leadership, leadership, leadership, or the lack of it..."for want of a nail, the kingdom was lost".
I recommend a great book, Attack and Die, by McWhiney and Jamieson, that goes into "Civil War Military Tactics and the Southern Heritage" in great detail if you want to order it.
Nonetheless the rebel yell had to have figured into the equation. I will look it up next and report back!!!