The development of B-25 began in 1938. After a series of improvements, NA-62 was demonstrated to USAF and was accepted in the production. First production version was flown on August 19, 1940. The fuselage is narrow with a large radiator under the fuselage aft of the wings. Low-set wings are unswept.
Tailplane is unswept with squared tips.
Landing gear with tail wheel is retractable. First prototype NA-73 was flown on October 26, 1940. The fuselages had P-51H wings and were connected by a rectangular wing. Instead of standard P-51 tailplanes, a single rectangular tailplane connected the fuselages in the rear. The fuselage is round with a teardrop canopy and a round air intake in the slanted nose.