The North American XB-21 was submitted to the Army Air Corps in the spring of 1937 for evaluation as an improved twin-engine bomber. The improved Douglas B-18A was the competitor for the XB-21. Douglas could produce the B-18A much cheaper than North American could build the XB-21 ($64,000 vs. $122,000), so the competition was won by Douglas. Five service test models of the XB-21 were ordered as YB-21, but the contract was canceled before any aircraft were built.
The XB-21 featured power nose and ventral turrets with a single .30-cal. machine gun in each; however, the nose turret was removed and replaced by a solid metal shell and the ventral (top) turret was removed completely during testing. The XB-21 was capable of carrying a 10,000 pound bomb load for about 600 miles and 1,960 miles with a 2,200-pound bomb load.
Model NA 21
TECHNICAL NOTES: Armament: Five .30-cal. machine guns and 10,000 lbs. of bombs Engines: Two Pratt & Whitney R-2180-1 supercharged radials of 1,200 hp each Maximum speed: 220 mph at 10,000 ft. Cruising speed: 190 mph Service ceiling: 25,000 ft. Range: 1,960 miles with 2,200 lbs. of bombs (600 miles with 10,000 lbs. of bombs) Span: 95 ft. 0 in. Length: 61 ft. 9 in. Height: 14 ft. 9 in. Weight: 40,000 lbs. maximum weight Crew: Six (eight with the nose and ventral turrets) Serial number: 38-485