We get black helicopters at all hours on a fairly regular basis - we're a few miles from the base, and this particular army base is really more for research than active training, but there is some traffic. Haiku, the sheltie in my avatar, frequently demands I let him outside to chase the big mean nasty helicopters away, even if it's 2 AM when they fly over. As far as he's concerned, he's doing a fantastic job - no helicopters have landed in our yard yet!