Other matters of note and corrections concerning the Valkyrie XB-70A:
The two prototypes produced, known as AV/1 (Air Vehicle/1) which bore tail number 20001 and AV/2 which bore 20207, were subtly different aircraft. AV/1 was constructed using extensive wind tunnel testing and some 18 months worth of computer modeling (remember, this is the 1960's), while AV/2 incorporated many design modifications that were made after testing of AV/1. These included changes to the canards, the nose and other minor structural, aerodynamic, and control aspects of the craft.
Problems with the AV/1 were manifold, owing to the number of new technologies and construction methods employed. These ranged from the first large scale use of honeycombed reinforced surface panels to a hydraulic system that operated at 4000psi, some 35% higher pressure than any other aircraft at the time. The problems with the honeycomb surface panels were so severe that they separated in flight the first time the plane broke Mach 3, after only one short foray to its maximum speed, AV/1 had a speed limit placed upon it: Mach 2.5 (1,850 mph/2980 kph).
AV/2 was plagued by fewer gremlins. It performed exceptionally, cruising in excess of Mach 3 without any difficulties. Even after the possibility of production was ruled out, it was obvious that AV/2 would be an ideal test bed for technologies necessary for a supersonic transport (SST) as well as general sonic boom research.
On the morning of June 8th, 1966, AV/2 performed a few passes over some recording instruments at Mach 1.4, 32,000ft above sea level. Then, at the request of GE it joined a formation of 4 other aircraft powered by GE; an F-4 Phantom II, an F-104 Starfighter, a T-38 Talon and an F-5 Freedom Fighter (also known as the F-5 Tiger). The aircraft flew in close formation for some 45 minutes, with the photographers constantly requesting a tighter formation; then just as formation was being broken for return to Edwards Airforce Base disaster struck. The F-104 that had been flying off of the XB-70's starboard wingtip was caught in the wake vortices generated by the massive delta wing. It was hurled into the wing and then carried with the airflow up over the back of the aircraft, where it smashed into both vertical stabilizers (tails). The pilot of the F-104, Joseph A. Walker, was killed instantly.
The XB-70 continued to fly for roughly another minute before it too lost control. The pilot, Al White, was able to eject safely, though he was injured in the 33G impact to which he was subjected upon landing. Carl Cross, the co-pilot who was making his first XB-70 flight, died when the XB-70 impacted in a flat spin in the desert just north of Barstow, California.
To this day, you can find parts of that XB-70 littering the desert.