So, go to this website (I have it in my favorites), type in the acronym and presto: answer. And if the acronym is unusual enough (like OODA) not to pop up right away, you're shunted over to another website, the Acronym Finder.
Try it - you'll like it.
http://www.militarywords.com/result.aspx?term=HVT
Janet
p.s. OODA = observe, orient, decide, act, as in OODA loop.