- The North American XB-70 is one of the most unusual looking aircraft in aviation history, and only two were constructed. It was originally designed as a Mach 3 high-altitude bomber, but was later used as a research aircraft. This new book by John Campbell and Garry Pape gives a short, detailed history of the XB-70, including production, flight tests, and the fatal crash of Aircraft N.2 in 1965. Aircraft N.1 is now at the U.S. Air Force Museum at Wright-Patterson AFB.