The twin-turbojet X-3, the only one built, was designed to test sustained flight at twice the speed of sound. It also explored the use of very short wings and titanium airframe construction. The X-3 made its first test flight at Edwards Air Force Base, Calif., in October 1952. The X-3 was transferred to the museum in 1956. TECHNICAL NOTES: Engines: Two Westinghouse J34s of 3,370 lbs. thrust each (4,900 lbs. thrust with afterburner) Maximum speed: 650 mph (level flight), but designed for Mach 2 S