Model Variants (Including Prototypes)
Model 299 - Boeing Model Test Aircraft; fitted with 4 x Pratt & Whitney 750hp engines; later lost to an accident attributed to human error.
Y1B-17 - Thirteen ordered for further development; later redesignated to B-17.
Y1B-17A - Engine test aircraft (only one produced); later redesignated to B-17A model.
B-17B - First production model
B-17C - 38 such samples produced and fitted with 4 x Wright Cyclone engines generating 1,200hp each.
B-17D - Similar to C production model to which all existing C models were brought up to D model standard.
B-17E - Mass production model; Enlarged tail section.
B-17F - Improved defensive armament
B-17G - Improved variant; Bendix chin turret implemented.
B-17H - Modified air-sea rescue conversions; fitted with rescue equipment.
Fortress I - B-17C models as supplied to the RAF in 1941.
Fortress IIA - B-17E models as supplied to the RAF in 1942.
Fortress III - B-17G models as supplied to the RAF.
F-9C - B-17G models converted for reconnaissance; ten such models utilized.
PB-1W - US Navy / Coast Guard maritime surveillance models of which 24 were utilized.
PB-1G - US Navy / Coast Guard maritime surveillance models of which 16 were utilized.
TB-17H - Modified air-sea rescue conversions; fitted with rescue equipment.