The Douglas X-3 existed purely as a research aircraft, designed to study the barrier of sustained, supersonic jet-powered flight at speeds of Mach 2. During the 1940s, the jet engine continued to grow as a viable propulsion system for military aircraft. The alternative was rocket power but these systems were fuel-hungry and of limited tactical scope concerning fighters/interceptors. The turbojet suffered from some of the same limitations and this, in turn, would limit the range and performance of many designs of the post-war period. Consideration was given to hybrid-powered aircraft which retained use of a propeller-turning engine coupled with a rocket or turbojet engine for an increased boost. However, these did not reveal any dramatic performance benefits against the best piston-powered, propeller driven fighters of World War 2 and thereafter.
By the late 1940s, jets continued their evolution to the point that the next major conflict would give rise to the first jet-versus-jet duels in the skies over the Korean Peninsula. From the Korean War came the North American F-86 Sabre and Mikoyan-Gurevich MiG-15 "Fagot" fighters as well as other well-known types. Despite their sleek designs and jet propulsion systems, these aircraft were only able to reach Mach 1 speeds in a dive. What was sought were aircraft who could perform faster in a sustained way and go beyond the Mach 1 ceiling to stay there.
The X-3 followed such famous mounts as the Bell X-1 for the Americans. The new design was born from the work of Fancis Clauser, Schuyler Kleinhans, and Baily Oswald and became one of the most unique and easily identifiable research craft of the 1950s. The finalized design incorporated a fuselage just slim enough to house the necessary 2 x Westinghouse J34 afterburning turbojets in a side-by-side arrangement as well as the requisite fuel stores, control systems, undercarriage and cockpit. The main wing appendages could therefore be left quite short in length and of a straight design approach, their thin chords providing the least amount of resistance possible. The tail section was an extended piece of the fuselage and mounted very small-area tailplanes. The cockpit was embedded into the rounded fuselage with the canopy well-integrated while offering limited vision for the pilot. At the front, the aircraft came to a very sharp point in keeping with the X-3's sleek design. The aircraft was also given a retractable tricycle undercarriage which allowed it to taxi, take-off and land on its own without the need for a mothership to launch it. The X-3 was notable for being one of the first aircraft to utilize titanium in its construction.
Due to its highly unorthodox, rather futuristic shape, the X-3 became known as the "Stiletto" due to its dagger-like appearance.
The United States Air Force commissioned for two flyable X-3 aircraft during June of 1945 (World War 2 would end in August of that year). Manufacture of the pair was then formally approved during June of 1949. Initially, the program sought use of 2 x Westinghouse J46 afterburning turbojets outputting at 6,600lbs thrust each but these were eventually replaced by the lower-thrust Westinghouse J34 of 4,850lbs thrust (each) when the expected J46s could not meet the program demands. Nevertheless, work on the X-3 proceeded into the early 1950s to which the first aircraft made a first flight on October 15th, 1952 across a dry lakebed during a high-speed taxiing run. In December of 1953, the aircraft was passed on to the United States Air Force for further flights.
By this time, many shortcomings in the X-3 were revealed. Chief among these was the X-3s lack of power which degraded performance. Pilots cited poor controlling as well, making the X-3 something of a lethal aircraft to fly for any period. Indeed, the design failed to net the expected Mach 2 speeds in sustained flight and only ever was able to reach the maximum speed of Mach 1.2 through a 30-degree dive. Even the Mach 1.0 barrier proved elusive, the X-3 required to enter a 15-degree dive. More or less a failure of its test program, the X-3 was retired in short order. Its final flight occurred on May 23rd, 1956 (for a total of 51 flights) and the planned second X-3 was never completed. The sole X-3 then became a museum showpiece at the United States Air Force Museum of Dayton, Ohio.
Despite it never achieving its program goals, the X-3 provided valuable research data in the area of "inertia coupling", a lethal aerodynamic load concentration phenomena that could endanger both aircraft and crew in seconds (this phenomena led to delays in brining the famous North American F-100 Super Sabre into being). The X-3's razor-thin wings also influenced those seen on the upcoming Lockheed F-104 "Starfighter" which utilized similar short, slim "wing-stubs" in its configuration.