A friendly Drill Instructer pulled me aside and explained a better way, the Marine Corps OOH-RAH, which in 1977, Not One person in the Army that I heard of ever used anything similar to.
So, I credit the USMC with the origin of OOH-RAH. I heard some Marine cut it from a Russian term URRAH, loosely translated into:Kill them all. That could be false, I dunno.
........and sounds funny when WMs say it.