The B-339E, or Brewster Buffalo Mk I as it was designated in British service, was initially intended to be fitted with an export-approved Wright R-1820-G-105 Cyclone engine with a (peak takeoff) engine. The Brewster aircraft delivered to British and Commonwealth air forces were significantly altered from the B-339 type sold to the Belgium and French forces in accordance with their purchase order. The Brewster factory removed the Navy life raft container and arrestor hook, while adding many new items of equipment, including a British Mk III reflector gun sight, a gun camera, a larger fixed pneumatic tire tail wheel, fire extinguisher, engine shutters, a larger battery, and reinforced armor plating and armored glass behind the canopy windshield.