"The High and Mighty One". Built as B-52A converted to NB-52A to carry/launch X-15. To AMARC Oct '69. Now on display at Pima, Air Museum. The horizontal lines are non-powered flights of the X-15, slanted lines are powered flights.
NB-52A Stratofortress "The High And Mighty One", this aircraft, one of 3, was used as a test vehicle and carried the X-15 aloft. Each X-15 symbol represents an X-15 flight that was launched from this aircraft.