The B-17D was an improved version of the B-17C. Changes included an improved electrical system, more extensive armor plating, self-sealing fuel tanks, and cowl flaps. One of the only external differences, and the easiest way to distinguish between the C and D, was the cowl flaps present on the B-17D. The Army Air Corps ordered 42 Ds in 1940. Twenty B-17Cs were sent to the RAF, but the remaining 18 aircraft were converted to the B-17D standard.
A flight of B-17s en route to Hawaii on Dec. 7, 1941, were assumed to be the large formation of aircraft tracked on radar early that Sunday morning. This formation turned out to be the carrier-based attack and fighter aircraft of Japan. The B-17s arrived later in the day and became the first B-17s to see combat in the Pacific Theater of Operations during World War II.
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: 40-3059 to 40-3100