The Douglas Skystreak (D-558-1 or D-558-I) was an American single-engine jet research aircraft of the 1940s. It was designed in 1945 by the Douglas Aircraft Company for the U.S. Navy Bureau of Aeronautics, in conjunction with the National Advisory Committee for Aeronautics (NACA). The Skystreaks were turbojet-powered aircraft that took off from the ground under their own power and had unswept flying surfaces. Development The D558 program was conceived as a joint NACA/U.S. Navy research program for transonic and supersonic flight. As originally envisioned, there would be three phases to the D558 program: a jet-powered airplane, a mixed rocket/jet-powered configuration, and a design and mockup of a combat aircraft. A contract for design and construction of six D558-1 aircraft for the first phase was issued on 22 June 1945. The original plan had been for six aircraft with a mixture of nose and side air inlets and varying wing airfoil sections. That plan was quickly reduced to three aircraft of a single configuration with a nose inlet. Plans for the second phase with mixed rocket/jet propulsion were also dropped. Instead, a new aircraft, the D558-2, was designed with mixed rocket and jet propulsion for supersonic flight. Construction of the first 558-1 began in 1946 and was completed in January 1947. The fuselage used magnesium alloys extensively, while the wings were fabricated from more conventional aluminum alloys. It was made of HK31, which is 3% thorium and 1% zirconium and the rest magnesium, being much lighter than inconel and having a much higher heat capacity. The airframe was designed to withstand unusually high loads of up to 18 times gravity due to the uncertainties of transonic flight. The forward fuselage was designed so that it, including the cockpit, could be jettisoned from the aircraft in an emergency. The aircraft was configured to carry more than of test equipment, including sensors (primarily strain gauges and accelerometers) in 400 locations throughout the aircraft. One wing was pierced by 400 small holes to enable aerodynamic pressure data to be collected. The Skystreaks were powered by one Allison J-35-A-11 engine (developed by General Electric as the TG-180) — one of the first axial-flow turbojets of American origin — and carried 230 US gallons (871 L) of jet fuel (kerosene). Operational history All the Skystreaks were initially painted scarlet, which led to the nickname crimson test tube. NACA later had the color of the Skystreaks changed