Some years ago I travelled to France to crew for my Dad who was bringing his small sailboat back across the channel to the UK.
About halfway across, Dad had gone below and I was sailing along in the middle of nowhere, with nothing anywhere near us.
Suddenly, I heard a very loud "ba boom" and thought, hmmm, I wonder what that was?
Dad came running up the steps from below saying "what have we hit, what have we hit" (thanks for your confidence in me Dad). Nothing I said, very offended. We both looked around seeing nothing and eventually I looked up to see the beautiful sight of a Concorde miles above us flying Westwards in a clear blue sky.
I guess the " ba boom " was the two shock waves of the nose and the leading edge sweeping past us.
Terrific sight. Terrific machine.