I could literally write a small pamphlet about the history of the SR-71 in milspeak, but that would just take up too much space... so I'll tell you some things generally not known about the Habu: airframe stressed for Mach 4 flight, stellar and inertial linkage for precise navigation (pre-Sat), max speed sustained Mach 3.4 (at 3.5 engines degrade, faster and the engines would come apart and blow), max height avg= 84,000 ft, max est. ceiling 102,000 ft (some experts claim between 100-120,000 ft), airframe 90% titanium, tanks only seal at 2000 mph (they leak on the ground), special tankers required for operations due to special high flash fuel, pilot and RSO wore spacesuits similar to shuttle crews, and the vertical tails were canted slightly inward to deflect radar (although not required)... so it had some stealth! Also, there was a plan to build a faster delta version, but was denied due to budget constriants (32 Habus were enough).