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!
I’m glad some one can confirm what my teacher witnessed on his radar. I read on a wiki somewhere that the J-58s could theoretically push the SR-71 to about Mach 5.0.
It is amazing what our technology could do in the 50s and 60s. Just imagine what our most advanced stuff can do today.