Quote: With a Radar Cross Section equivalent to a small light aircraft, the SR-71 appeared on enemy radar screens too late for a missile computer to estimate its direction for a successful shoot-down.
How true! As a co-op engineering student, I worked for an Eglin AFB contractor, with two of my quarters spent at its A7 site, which had a copy of the Soviet SAM-2 S-band missile radar. One day a Blackbird was to fly by, so we set out to see it. At that time, we had also had a copy of the SAM's VHF acquisition radar in the parking lot, so I was tasked with watching its PPI scope. We were told where the Blackbird was inbound and outbound, but neither radar picked it up. Its radar profile was small and there was little time. I got two sweeps to look for it inbound and two outbound. Never saw it.
Time is a critical factor in intercepts. Those who'd like to know the specifics might read Stephen Bungay's definitive look at the Battle of Britain The Most Dangerous Game. German bombers and their fighter escorts would form up on the north of France and when it was ready they'd head out for England. The distance was so small that the window of time for Hurricanes and Spitfires to take off and reach a swoop-down attitude at the proper location was just two or three minutes from the time when the target of the attack became clear. It took incredibly quick decision making and coordination to get the fighters up and correctly positioned to do that. Fortunately, the Germans never quite realized what they were up against.
And to be frank, I suspect we're similarly underestimating just how much effort the Russians are devoting to their air defenses. They did not like being taunted by the Mach-3 SR-71. They're getting ready for the Mach-6 SR-72.