The deferred deliveries of the P-40 to the USAAAC were picked up again with the P-40B. In September 1940, 131 P-40Bs were procured by the Army to replace the deferred P-40s The P-40B (Model H81-B) differed from the P-40 in having an extra 0.30-inch machine gun installed in each wing, bringing the total to four 0.30-inch guns in the wings. The two 0.50-inch guns in the fuselage were retained. The engine was still the V-1710-33. Serials were 41-5205/5304 and 41-13297/13327 (c/ns 15973/16103).
The first P-40B flew on March 13, 1941. The airplanes were delivered in full camouflage. In contrast to the earlier P-40, the tail stripes and upper right and lower port wing stars were no longer present, but a star now appeared on each side of the fuselage. The P-40B retained the same dimensions of the P-40, but weight was increased to 5590 pounds empty, 7326 pounds gross, and 7600 pounds maximum loaded. Because of the additional weight, the P-40B had an inferior performance to the P-40, maximum speed being 352 mph, service ceiling being 32,400 feet, and initial climb rate being 2860 feet per minute. Normal range was 730 miles, but a maximum range of 1230 miles could be attained at the minimum cruise settings.
The export equivalent of the P-40B was the Tomahawk IIA (Model H81-A2). They differed from the American version by having the wing guns replaced by four 0.303-inch Brownings. 110 were produced for the RAF. RAF serials were AH881/990. 23 of these planes were transferred to the USSR, and one (AH938) went to Canada as an instructional airframe.