[Jack Hydrazine]

"...at speeds of up to mach 3.5..."

A teacher of mine, who was a retired air traffic controller, clocked the SR-71 doing 3,500 kts when he was doing ATC. Even though the speed was listed as "SC" (Speed Classified) he drew up a couple of marks on his monitor that specified a given distance and then he timed it.

5,000kts. x 1.15 = 5,750mph/760mph (speed of sound assuming ISA) = Mach 5.3.

This wiki says:

http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
"The only American engines designed to operate continuously on afterburner, the J58 engines were most efficient around Mach 3.2,[43][44] and this was the Blackbird's typical cruising speed."

J-58 static test.

[Rembrandt]

I was a Navy Viet ling monitoring the NVN air forces. We got advance notice of SR-71 flights out of Okinawa. We watched the NVN track it as it went West across the South China Sea and two minutes later it was over Laos after having crossed North Vietnam, easily 5.3 Mach. We also tried to figure out the speed and were astounded.

The blackbird carried photographic equipment which ran continuously and could produce images from 100K feet which could be deciphered and yield the exact height of a person or the license number of a vehicle even through clouds. That was in the latter ‘60’s!