A story from an SR-71 Pilot
We trained for a year, flying out of Beale AFB in California, Kadena Airbase in Okinawa, and RAF Mildenhall in England. On a typical training mission, we would take off near Sacramento, refuel over Nevada, accelerate into Montana, obtain high Mach over Colorado, turn right over New Mexico, speed across the Los Angeles Basin, run up the West Coast, turn right at Seattle, then return to Beale. Total flight time: two hours and 40 minutes.
One day, high above Arizona, we were monitoring the radio traffic of all the mortal airplanes below is. First, a Cessna pilot asked the air traffic controllers to check his ground speed.
"Ninety knots," ATC replied.
A twin Bonanza soon made the same request.
"One-twenty on the ground," was the reply.
To our surprise, a Navy F-18 came over the radio with a ground speed check. I knew exactly what he was doing. Of course, he had a ground speed indicator in his cockpit, but he wanted to let all the bug-smashers in the valley know what real speed was.
"Dusty 52, we show you at 620 on the ground," ATC responded.
The situation was too ripe. I heard the click of Walter's mike button in the rear seat. In his most innocent voice, Walter startled the controller by asking for a ground speed check from 81,000 feet, clearly above controlled airspace.
In a cool, professional voice, the controller replied, "Aspen 20, I show you at 1,982 knots on the ground." We did not hear another transmission on that frequency all the way to the coast.
I believe this story came from Brian Shul's book, "Why I Fly"