In 1941, as a result of air combat reports coming in from Europe, modifications were introduced into the North American B-25 production line at Inglewood beginning with the 25th aircraft built, resulting in a change in designation to B-25A.
The B-25A introduced armor protection for the crew, including a 3/8-inch armor plate added to the pilot's, co-pilot's and bombardier's seats as well as to the gunner's compartments. The aircraft was also equipped with self-sealing fuel tanks, which reduced total fuel capacity from 912 to 694 US gallons, although provision was made for the installation of a 418 gallon tank in the bomb bay for ferrying. This made for a significant increase in weight, resulting in a slight degradation in the performance.
The first Air Corps operational unit with the B-25A was the 17th Bombardment Group at McChord Field, which included the 34th, 37th, and 95th Squadrons, plus the attached 89th Reconnaissance Squadron. This outfit, which formerly flew Douglas B-18s, moved to Pendleton, Oregon in June of 1941. Other B-25As were sent to the 30th Bombardment Group at New Orleans, the 43rd Bombardment Group at Bangor, Maine, the 39th Bombardment Group at Spokane, Washington, and the 44th Bombardment Group at MacDill Field in Florida. One B-25A went to Wright field for tests.
A total of 40 B-25As were built before the production line switched over to the B-25B version.
40-2189/2228 North American B-25A Mitchell company numbers 62-2858/62-2897
Engines: Two Wright R-2600-9 Double Cyclone fourteen-cylinder air-cooled radials, each rated at 1700 hp for takeoff and 1500 hp at 2400 rpm. Equipped with Bendix Stromberg PD-13E-2 carburetors. Performance: Maximum Speed 315 mph at 15,000 feet. Service ceiling 27,000 feet, Cruising speed 262 mph. Climb to 15,000 feet in 8.4 minutes. Range 1350 miles with 3000 pounds of bombs. Weights: 17,870 pounds empty, 27,100 pounds maximum loaded. Dimensions: wingspan 67 feet 6.7 inches, length 54 feet 1 inche, height 15 feet 9 inches, wing area 610 square feet. Fuel: two forward wing tanks, total 368 gallons. Two rear wing tanks total 324 gallons. One droppable bomb bay tank, 418 gallons. Armament: One 0.30-inch machine gun in flexible mount in the nose. One 0.30-inch machine gun in a flexible dorsal position. One 0.30-inch machine gun in flexible waist position. One 0.50-inch machine gun in flexible tail position.