North American Aviation's first twin-engined military aircraft, the NA-21 prototype was constructed at North American's factory in Inglewood, California, where work on the aircraft began in early 1936. Evaluated against the Douglas B-18 Bolo, it was found to be considerably more expensive than the rival aircraft, and despite the ordering of a small number of evaluation aircraft, only the prototype was ever built. The North American XB-21 (manufacturer's model designation NA-21) and sometimes referred to by the name 'Dragon', was a prototype bomber aircraft developed by North American Aviation in the late 1930s, for evaluation by the United States Army Air Corps.
