The initial concept for the Model 27 was for the fighter to be carried half-exposed under the B-29, B-35, or B-36. The USAAF rejected this proposal, citing increased drag, and hence reduced range for the composite bomber-fighter configuration. On 19 March 1945, McDonnell's design team led by Herman D. Barkey, submitted a revised proposal, the extensively redesigned Model 27D. The smaller aircraft had an egg-shaped fuselage, three fork-shaped vertical stabilizers, horizontal stabilizers with a significant dihedral, and 37° swept-back folding wings to allow it to fit in the confines of a bomb bay. The diminutive aircraft measured long; the folding wings spanned . Only a limited fuel supply of was deemed necessary for the specified 30-minute combat endurance. A hook was installed along the aircraft's center of gravity; in flight, it retracted to lie flat in the upper part of the nose. The aircraft had an empty weight just short of . To save weight, the fighter had no landing gear. During the testing program, a fixed steel skid under the fuselage and spring-steel "runners" at the underside of the wingtips were installed in case of an emergency landing. Despite the cramped quarters, the pilot was provided with a cordite ejection seat, bail-out oxygen bottle, and high-speed ribbon parachute. Four machine guns in the nose made up the aircraft's armament.