Military slang; can basically mean anything apart from 'no'. General expression of enthusiasm. Something semi-meaningless to shout when psyching up for rowing all-out.
See [here] for a brief explanation, also [here] for the same a different spelling but a better definition. [George W. Bush has had this word used at him.] And I believe he used himself, once, but I can't find the news story I saw that in.
"Those soldiers in the link sound really dumb!"-- King DJ
It would appear the actual spelling is HUA. An explanation of the origin of the term can be found [here] and the best use I've come across are the examples at the bottom of [this page] --Edith.
Ah that's a great word. :-) Brings back all the good bits in "scent of a woman".