I heard the story of its origin from a retired Vietnam era Special Forces guy in 1990 who heard it from a Korean War guy in the 1960's. Similar story about being ordered to take an objective (hill top in Korea) during the din of battle and the response was a mis-heard "who us?".
PSG (Platoon Sergeant) - "HUA!!"(you could add SNAFU to that)
2. Depending upon the pronunciation it might also be an alternate spelling and way to say the word "whore." Specific to New York and New Jersey dialects.
2. "Oh my Gawd...she is such a Hooah!"