The XB-70 Valkyrie is a bomber designed during the cold war to deliver a nuclear weapon deep into Soviet territory. With a top speed over Mach 3 and a service ceiling over 77,000 altitude it was able to outrun any interceptor aircraft of the day.
There were only two prototypes built. The first (No 62-001) on Sept. 21, 1964. Testing of "Ship #1" found the aircraft to have poor directional stability above Mach 2.5. The first prototype only made a single flight above Mach 3.
Wind tunnel studies and testing at the NASA Ames Research Center at Moffett Field, CA, resulted in the construction of the second XB-70A (No 62-207). This aircraft had an additional 5 degrees of dihedral on the wings which resulted in much better handling. "Ship #2" made its first flight on July 17, 1965, and achieved Mach 3 for the first time on Jan. 3, 1966. The aircraft made a total of nine Mach 3 flights by June.
The second prototype made at least 4 sustained flights at Mach 3 and 70,000 ft of significant duration:
Feb 17, 1966, Flight # 2-22, 15 minutes Mach 3 at 70,000 ft
April 8, 1966, Flight #2-32, 16 minutes Mach 3 at 70,000 ft
April 12, 1966, Flight #2-33, 20 minutes Mach 3 at 70,000 ft
May 19, 1966, Flight #2-39, 32 minutes Mach 3 at 70,000 ft
The second prototype was lost on June 8, 1966, from a midair collision with NASA F-104N chase plane flown by Joe Walker.