Its primary mission was to investigate the design features of an aircraft suitable for sustained supersonic speeds, which included the first use of titanium in major airframe components.

Douglas designed the X-3 with the goal of a maximum speed of approximately 2,000 mph (3,200 km/h),[2] but it was seriously underpowered for this purpose and could not even exceed Mach 1 in level flight.

The X-3 featured an unusual slender, streamlined shape having a very long, gently-tapered nose and small trapezoidal wings.

The aim was to create the thinnest and most slender shape possible in order to achieve low drag at supersonic speeds.

The extended nose was to allow for the provision of test equipment while the semi-buried cockpit and windscreen were designed to alleviate the effects of "thermal thicket" conditions.

Due to both engine and airframe problems, the partially completed second aircraft was cancelled, and its components were used for spare parts.

During a high-speed taxi test, Bridgeman lifted the X-3 off the ground and flew it about one mile (1.6 km) before settling back onto the lakebed.

These showed that the X-3 was severely underpowered and difficult to control; its takeoff speed was unusually high—260 miles per hour (230 kn; 420 km/h).

The poor performance of the X-3 meant only an abbreviated program would be made, to gain experience with low aspect ratio wings.

The initial flights looked at longitudinal stability and control, wing and tail loads, and pressure distribution.

The mass of its engines, fuel and structure was concentrated in its long, narrow fuselage, while its wings were short and stubby.

It showed the dangers of roll inertia coupling, and provided early flight test data on the phenomenon.