The SR-71, tail number 844, had been displayed for years at NASA’s Armstrong Flight Research Center, which is located alongside Edwards Air Force Base.' A famed SR-71 Blackbird spy plane has disappeared from a California military facility, fuelling speculation after NASA recently unveiled an image resembling the legendary aircraft while announcing plans to expand its experimental X-plane programme. The SR-71, tail number 844, had been displayed for years at NASA’s Armstrong Flight Research Center, which is located alongside Edwards Air Force Base.' Satellite imagery indicates that the aircraft has not been visible at the facility since at least May 17, according to Aviation Week defence editor Steve Trimble, who first reported its disappearance. The timing has attracted attention because NASA Administrator Jared Isaacman recently unveiled a silhouette resembling an SR-71 during the All-In Summit in Los Angeles. Isaacman said NASA was rebuilding its fleet of experimental X-planes and returning to high-speed and high-altitude flight research. "In the service of the first A [aeronautics] in NASA, we are rebuilding our X-plane fleet. The X-59 is researching quiet supersonic flight, but it’s just the beginning," Isaacman told The War Zone. "It will not be long before NASA once again is flying as high and as fast as we had in decades past, and then even more." When an image resembling a Blackbird appeared during a live interview afterwards, Isaacman added to the speculation by asking: "You sure that’s a Blackbird?" The missing aircraft is significant because it was not an ordinary museum display. Originally designated US Air Force serial number 61-7980, it was the final SR-71 produced and the last one to fly. Its final flight took place in 1999. According to Aviation Week sources, the aircraft was moved into a hangar earlier this year for an inspection. The publication reported that the combination of the aircraft's disappearance and Isaacman's comments has raised the possibility of a programme involving the aircraft returning to flight more than 26 years after its final mission. NASA has not confirmed that such a programme is underway. The agency has instead pointed to its broader plans for experimental aircraft designed to advance high-speed and high-altitude flight. The California desert has long been used to test experimental aircraft, and NASA is continuing that work with the X-59.