The Army Air Corps ordered 38 improved B-17Bs as B-17C in 1940. The B-17C changed from 1,000-hp to 1,200-hp Wright R-1820-65 radial engines. Flat sliding gun panels were installed instead of waist gun blisters, providing greater crew safety and cleaner design. The ventral gun blister was replaced by a "bathtub" turret also.
Twenty B-17Cs were transferred to the RAF (Fortress I), which used them during the early stages of World War II. The remaining 18 C models were modified to the D model configuration and became second line RB-17Ds late in their service lives.
TECHNICAL NOTES: Armament: One .30-cal. and six .50-cal. machine guns and 4,800 lbs. of bombs Engines: Four Wright R-1820-65 turbo-supercharged radials of 1,200 hp each Maximum speed: 323 mph at 25,000 ft. Cruising speed: 227 mph Service ceiling: 37,000 ft. Range: 3,400 miles (maximum ferry range) Span: 103 ft. 9 in. Length: 67 ft. 11 in. Height: 15 ft. 5 in. Weight: 48,500 lbs. gross weight (actual - normal load) Serial numbers: 40-2042 to 40-2079