XB-70
It was built during the cold war to out run fighters and carry a nuclear payload since the B-52 was pretty much a sitting duck to fighters. It flew at Mach 3 once, and funding was cut off partially since it was costly and second it had a fatal air collision during a photo shoot. So it never made it to production. It was used by NASA for testing before it was sent to the Air Force musuem in Dayton, Ohio. I've seen it in person and it's gorgeous.
Performance
Maximum speed: 2,056 mph. (Mach 3.1) at 73,000 ft.
Cruising speed: 2,000 mph. (Mach 3.0) at 72,000 ft.
Range: 4,288 miles
Service Ceiling: 77,350 ft.





Pictured with it's Three Wingtip Configurations


Pictured with an X-15
Only pictured seen with the two prototypes
Cockpit of XB-70



Engines of XB-70

The Crash of the number 2 XB-70, an F-104 collided with it during the photo shoot. The pilot of the F-104 died obviously in the flamming aircraft you can see, and the one of the two pilots survived the in the XB-70.







Video of the XB-70 landing
http://www.dfrc.nasa.gov/gallery/movie/XB-70/index.html[/img]