X-3 Stiletto

The distinctively slender Douglas X-3 Stiletto (only one was built) was active between 1952 and 1956. A rare bird among the X-Planes, it was designed to take off from the ground and under its own power. But early flights, NASA said, "showed that the X-3 was severely underpowered and difficult to control. Its takeoff speed was an astonishing 260 knots! More seriously, the X-3 did not approach its planned performance. Its first supersonic flight required that the airplane make a 15-degree dive to reach Mach 1.1. The X-3's fastest flight, made on July 28, 1953, reached Mach 1.208 in a 30-degree dive."

Still, the control problems for the X-3 helped researchers investigating similar problems with production model fighter jets, and its high-speed takeoffs and landings led to improvements in tire technology, according to NASA. And it was notable as well for its pioneering use of titanium.