The B-type wing was structurally an A type modified to carry one 20 mm Hispano cannon per wing, which replaced the two inner .303 machine guns. The retractable underwing landing lamp was repositioned. The cannon was installed in the innermost machine gun bay, next to the wheelwell, while the second gun was deleted altogether. The area where the inner guns’ ammunition trays had been located, outboard of the cannon bay, was converted into a compartment to accommodate the 60-round drum magazine for the cannon. The upper and lower wing skins now incorporated blisters to clear the large ammunition drum (the underwing blisters came in two different shapes). The remaining outer pairs of .303’s were not changed at all. Only one armament suite could be fitted to a Spitfire with the B-type wing: Two 20 mm Hispano Mk II cannon, each with a 60-round drum, and four .303 caliber Browning machine guns in the outer positions, with 350 rpg. Alloy-covered ailerons were standardised on this wing type.