When I was working security at Thames Shipyard in NL, I got a few good surprises. The first was an fighter going down the river at about 50', under the bridge and over the railroad bridge at about 5:30am. The second was some sort of ceremony at the Coast Guard academy, two choppers in formation with a private jet at about 100' right over my guard shack. That was one of the loudest things I have ever heard, and the choppers kicked up a bunch of dust in the shipyard lot.