BradG wrote:If in doubt, err on the inclusive side. Makes things more interesting that way.
There's no doubt in regard this program - it was a joint effort between USAF,USN & NASA. It was to the most part funded by the US military and run/overseen by NASA. USAF provided the launch a/c - BUFFs as we know. The majority of the funding for the X-15 came from the USAF. X-15 flew with both military and civilian pilots right through to the end of the program. It was not like other X programs when the military was finished, they handed over the rocket planes to NASA as they did with X-1, D-558 II, etc. X-15 carried the "Stars & Bars" and USAF serial numbers so in my mind it cannot be considered a civilian aeroplane. The program itself though was a joint effort between all parties concerned.
Pilots were both military and civilian. One USAF pilot was lost - Maj. Mike Adams, when he lost control of X-15 No.3 on re-entry. He got into a hypersonic flat spin, recovered from that but the pitch dampers went and he got into a neck snapping pitch up/down exceeding the structural limits of both his neck and the X-15 itself tragically. The high speed runs were largely done in the X-15A2 - the stretched version with the large externals. USAF Major "Pete" Knight flew the Bull to it's fastest speed of Mach 6.7 - so fast that parts started to melt. It was rebuilt but never flew again after that flight.
X-15 pilots include:
X-15 pilots in order by dates of first flights # of Flights
A. Scott Crossfield, North American Aviation, 14
Joseph A. Walker, NASA, 25
Robert M. White, United States Air Force (USAF), 16
Forrest S. Petersen, United States Navy, 05
John B. McKay, NASA, 29
Robert A. Rushworth, USAF, 34
Neil A. Armstrong, NASA, 07
Joe H. Engle, USAF, 16
Milton O. Thompson, NASA, 14
William J. Knight, USAF, 16
William H. Dana, NASA, 16
Michael J. Adams, USAF, 07
Total Number of Flights: 199
So, X-15 was a military aircraft but operated/managed by a government/civilian organisation in a joint arrangement with the USAF & USN. One cannot call the X-15 a civilian aircraft even though NASA oversaw its operation. Note too that NASA did not appoint the military test pilots to fly it - only NASA's own test pilots. If the X-15 was purely owned/operated by NASA as some other X-planes were, then indeed it would be civvie, but it wasn't.
https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-052-DFRC.html