In the 70's I was working in the Colorado River bottoms of Central TX. Those planes flew out of San Angelo (I think) where they trained. They would pop up to be painted by radar then fly for maybe 100 miles along the River, then pop up to be painted again. They sneak up on you with just a little hiss, just enough to get you to turn and look before they blow by you at 50' of altitude, causing you to about load your drawers and did make me drop to the ground. Loud don't describe it. God bless our troops.