The Model 299 was the original bomber design built by Boeing to fulfil an August 1934 requirement by the United States Army Air Corps for a bomber capable of carrying 2,000 lb (907 kg) of bombs 2,000 mi (3,218 km) at 200 mph (322 km/h).
The 299 was powered by four Pratt & Whitney S1EG Hornet radial engines rated at 750 horsepower (560 kW) each at 7,000 feet (2,100 m), giving a maximum speed of 236 miles per hour (380 km/h) and a maximum gross weight of 38,053 pounds (17,261 kg).
It carried a bomb load of eight 600 pounds (270 kg) bombs, with a defensive armament of five machine guns, with one in a nose turret and one each in dorsal and ventral mounts and two in waist blisters.
The aircraft went through several alterations in each of its design stages and variants.
Of the 13 YB-17s ordered for service testing, 12 were used by the 2nd Bomb Group of Langley Field, Virginia, to develop heavy bombing techniques, and the 13th was used for flight testing at the Material Division at Wright Field, Ohio.
Experiments on this aircraft led to the use of a quartet of General Electric turbo-superchargers which would become standard on the B-17 line.
A 14th aircraft, the YB-17A, originally destined for ground testing only and upgraded with the turbochargers, was redesignated B-17A after testing had finished.