First time I saw it done was in ROTC, and my recollection is about the same as Pete's- the NCO showed us how, but I didn't get a warm fuzzy on how to do it and I didn't get any hands on (although I know I wasn't complaining at the time, I was freezing my butt off). Later, as a PL, I made my squad leaders teach me how to do it, but I don't recall having to ever do it myself (I had a good track driver who took care of it before the LT could mess it up).