The radical Douglas X-3 Stiletto was built primarily of titanium, and was intended to test high speed flight and low-aspect ratio wing design. Initial requirements indicated the aircraft would carry the J-46 engine and be capable of reaching cruising speeds above Mach 2.0. Problems with the J-46 engine, led Douglas engineers to substitute underpowered J-34 turbojets. Although the plane once achieved Mach 1.2 in a dive, it never went supersonic in...