The experimental NA-21 Dragon was North American Aviation’s first venture into multiengine design. It was a high-altitude bomber armed with single 0.30-inch (0.76-centimeter) machine guns in each of five positions, including in a ball-type turret in the nose. The NA-21 could carry 10,000 pounds (4535 kilograms) of bombs short distances or carry 2,200 pounds (998 kilograms) of bombs for 1,900 miles (3057 kilometers).

After a few small changes, the NA-21 was accepted for testing at Wright Field — now part of Wright-Patterson Air Force Base — but orders did not follow. The Air Force bought the single NA-21 in 1939 and redesignated it the XB-21.