Phileas,
As we all know, the SR71 [High Altitude Recconasance Aircraft] was developed from the A11/A12 Fighter developement prototype.
At that time, the USA were developing/had in service, the B58 Hustler, Mach2 at 60,000.....B70 Valkerie, Mach3 at 80,000
The USSR, had the Bounder,Blinder,Beauty,Backfire bombers,ALL High speed/High altitude in developement/in production.
Don't forget the Vulcan and Victor bombers, they reularily flew at 45-50,000, as did thr Canberra PR9
bf2005,
The "Beluga" was a "New Build" airframe designed and manufactured to replace the old "Super Guppy" aircraft
watp,iktch