Phonetic spelling of the military acronym HUA, which stands for "Heard Understood Acknowledged." Originally used by the British in the late 1800's in Afghanistan. More reciently adopted by the United States Army to indicate an affirmative or a pleased response.
1: Sgt: "Y'all got the game plan?"
PFC(s): "Hooah sargeant!"
2: Sgt: "Y'all ready for chow?"
PFC(s): "Hooah sergeant!"
Naval response indicating that an order has been received, is understood, and will be carried out immediately. In operational situations, this is usually shortened to simply "aye." In constrast to "Aye Aye sir," a response of "Yes Sir" usually indicates that the person understands but is contemplating performing the ordered task at a later time or date.
Ships Captain: "Lieutenant, I need those reports by 1400hrs."
Executive Officer: "Aye aye sir."
Officer of the Deck: "Helm, make your course 149."
Helmsman "Making course 149, aye."