The experimental NA-21 Dragon was North American's first venture
into multiengine design. It was a high-altitude bomber armed
with single .30-inch machine guns in each of five positions,
including in a ball-type turret in the nose. The NA-21 could
carry 10,000 pounds of bombs short distances or carry 2,200
pounds of bombs for 1,900 miles. After a few small changes, the
NA-21 was accepted for testing at Wright Field but orders did
not follow. The Air Force bought the single NA-21 in 1939 and
redesignated it the XB-21.