A motivational cry used by the United States Marine Corps. Sometimes also used as a general response to an order or question. Recon Marines in Korea (1953), traveling by submarine, often heard the dive klaxon which sounded like "Aarrugah." These Marines began using the word as a motivational tool, but it was too long and slowly became modified into what it is today. It was popularized during the 80s and 90s.
::Marine climbs rope at the end of the obstacle course and slaps the wooden beam at the top, yelling "Oorah!" ::
"Son, you good to go?"
"Grab that pack!"