It is short for something akin to "Heard and Acknowledged."
The differences matter incredibly much. Say Hoo-wah to a Marine and he will at best laugh at you for being weak sauce in the Army. Say Hoo-rah to a Soldier and he will laugh at you for joining the Corp. Nobody messes with SEALs (or Delta or the ilk). And I resemble the Air Force remark, military-industrial techno-complex represent
Bloodbird, fyi, resent not recent.
I know. Was a typo. I R Iletareate.
Somewhat besides the point, I have never been able to respect or even laugh at that 'not so friendly rivalry' among the US military branches. I heard a story once about an Army grunt that got beat up by a marine (both being civilians at the time) for, supposedly, getting the above wrong. I'm not entirely sure how true it is, but I've heard of similar cases at different times. Regardless, when you have a military where different branches apparently look down on each other and get to such cases, you have an issue, not an endearing quirk, and should look into fixing you fuck-up ASAP. I ran into a smaller case of this when I was in the military myself, but while I was, at the time, thinking of the above-mentioned issue, ours seemed more of an internal competition to excel and be better than said other branch, not a superiority issue that leads to looking down on your own fellow soldiers.
Having said all of that, learning where that over-rated expression comes from (or rather, what it's short-hand for) is nice, so thanks for sharing. Guess "Acknowledged" isn't cool enough for the military in the US. Now that I think about it, I guess it really isn't.