During 1935, in response to an Army request for a large, multiengine bomber, Boeing financed the design of the Flying Fortress prototype, the B-17 (Model 299). The B-17 went from the drawing board to flight test in less than 12 months. The low-wing, four-engine monoplane bomber combined the aerodynamic features of the XB-15 giant bomber, still in the design stage, and the Model 247 transport. The B-17 was built in astonishing numbers to support Allied demand. At one point, the Seattle plant rolled out 19 B-17s in 24 hours. Between 1935 and 1945, 12,731 B-17 Flying Fortress bombers were built by Boeing, Douglas, and Lockheed's Vega division plants across the country.