| Date | Event |
|---|---|
| June 1952 | NACA Committee on Aerodynamics recommends increase in research dealing with flight to Mach 10 and to altitudes from 12 to 50 miles. Also recommends that NACA endeavor to define problems associated with space flights at speeds up to the velocity of escape from Earth's gravity. |
| July 1952 | NACA Executive Committee adopts recommendations of Committee on Aerodynamics. |
| September 1952 | Preliminary studies of research on space flight and associated problems begun. |
| February 1954 | NACA Research Airplane Projects panel meeting discusses need for a new research airplane to study hypersonic and space flight. |
| March 1954 | Laboratories requested to submit views on most important research objectives and design requirements of a new research airplane. |
| May 1954 | NACA teams establish charaeteristics of a new research airplane, which subsequently becomes the X-15. |
| July 1954 | Proposal for new research airplane presented to the Air Force and Navy. |
| December 1954 | Memorandum of understanding for a "Joint Project for a New High-Speed Research Airplane" signed by representatives of the Air Force, Navy, and NACA. |
| December 1954 | Invitations issued by the Air Force to contractors to participate in the X-15 design competition. |
| September 1955 | North American Aviation, Inc., selected to develop three X-15 research airplanes. |
| February 1956 | Reaction Motors, Inc., awarded development contract for XLR-99 rocket engine, |
| December 1956 | X-15 mock-up completed. |
| September 1957 | Design configuration set. Construction starts. |
| October 1958 | Factory rollout of No. 1 airplane. |
| June 8, 1959 | First glide flight, No. 1 airplane. |
| September 17, 1959 | First powered flight, No. 2 airplane. |
| November 15, 1960 | First flight with XLR-99 engine. |
| February 7, 1961 | Last flight with interim rocket engine. |
| March 7, 1961 | First flight to Mach 4. |
| June 23, 1961 | First flight to Mach 5. |
| October 11, 1961 | First flight above 200 000 ft. |
| November 9, 1961 | First flight to Mach 6. |
| December 20, 1961 | First flight of No. 3 airplane. |
| July 17, 1962 | First flight above 300 000 ft. |
| November 9, 1962 | No. 2 airplane damaged during emergency landing. |
| June 27, 1963 | 50th flight over Mach 4. |
| January 28, 1964 | 100th flight in series. |
| June 25, 1964 | First flight of rebuilt No. 2 airplane. |
| August 12, 1964 | 50th flight over Mach 5. |
| August 14, 1964 | 75th flight over Mach 4. |
| October 15, 1964 | 50th flight by No. 1 airplane; 119th flight in program. |