“Hoo-ah” is an all-purpose exclamation, affirmation and declaration of pride that started in the Army but has since spread into the Air Force and Navy. The Marines have their own version—“Ooh-rah” (which is also sometimes used in the Navy). Until Scent of a Woman, the phrase was hardly ever heard outside of military bases.
The expression can mean many things, including: “Howdy!” “Good to go.” “Congratulations!” “I agree.” “Let’s go!” and “Have a nice day!” As retired Brigadier General Creighton Abrams, director of the Army Historical Foundation, explained, “It all started out as kind of an exclamation point, and that was just fine. Then it became something almost perfunctory, as in saying, ‘Hoo-ah’ instead of saying goodbye. Unfortunately, it’s become a bit much.”
The origin of the expression is obscure, which has not prevented a host of theories from arising. One is that it was a toast given by a Seminole chief at a banquet after truce talks during the Indian wars of the 1840s. The Department of Defense believes it might be an abbreviation of “heard, understood and acknowledged.” Some have suggested it may come from the Army adage “Hurry up and wait.” The author of a book of military expressions entitled Swear Like a Trooper suggests it may be derived from the British “Huzzah!” of the 1700s.
Steve Chawkins, “History of the Hoo-ah: Tracking an Exclamation,” Los Angeles Times, 4/15/03