Outwardly, the B-17B differed from the Y1B-17 only in having a revised rudder with larger area, larger flaps, and a revised nose that eliminated the greenhouse gun turret in the upper nose and the belly bomb-aiming window in the lower nose. The upper nose turret was replaced by a simple socket for a 30-inch machine gun in the extreme tip of the nose. The bomb-aiming window was replaced by an optical flat in the lower part of the Plexiglas nose fairing over which the famous Norden bombsight was mounted. The revised nose resulted in a decrease in overall length of 7 inches. A small plastic dome was added to the cabin roof. More-powerful R-1820-51 engines were fitted which delivered a maximum power of 1200 hp for takeoff and 900 hp up to 25,000 feet. Internally, many systems were changed and crew members were relocated. The brakes were changed from pneumatic to hydraulic.

The Norden bombsight was a gyro-stabilized bomb sight originally developed by Carl L. Norden and Capt. Frederick I. Entwistle. It was capable of quickly calculating the plane's forward velocity and drift and making corrections in order to achieve a hit. In later versions, the Norden bombsight was connected with the autopilot, and actually flew the plane during the final run into the target. In the press releases of the day, it was claimed to be so accurate that it could "put bombs in a pickle barrel". The Norden bombsight was considered so secret that it was installed, carefully covered, in the aircraft only immediately before takeoff and was taken out immediately after landing, always under the supervision of an armed guard.

The first B-17B (38-211) flew for the first time at Seattle on June 27, 1939. 39 B-17Bs were built in a single run at Boeing. However, the USAAC serial numbers were scattered over several batches, indicating how difficult it was at the time for the Air Corps to obtain funding--it could only order B-17Bs a few at a time.

All 39 of the B-17Bs were delivered to the USAAC between July 29, 1939 and March 30, 1940. The B-17Bs were issued to the 2nd, 7th, and 19th Bombardment Groups, except for the first example which was retained at Wright Field for tests.

In November of 1939, seven Fortresses flew from Langley Field to Rio de Janeiro, Brazil on a good-will mission. All planes returned safely with no major incidents, once again demonstrating the safety and reliability of the B-17 design.

Many B-17Bs were modernized in 1940-41 to use such such features as the flush-type side openings for 0.50-inch machine guns that had been introduced on the B-17C.

A B-17B serving with the 41st Reconnaissance Squadron of the 2nd Bomb Group based in Newfoundland attacked a U-boat on October 27, 1941. Although the U-boat was undamaged in the attack, this incident was the first in which bombs were dropped in anger by the Army Air Forces in action against German forces. Since the United States was officially not at war with Germany at the time, the incident was not reported in the press.

38-211/223 	Boeing B-17B
38-258/270 	Boeing B-17B
38-583/584 	Boeing B-17B
38-610 		Boeing B-17B
39-1/10     Boeing B-17B

Specification of Boeing B-17B:

Four Wright R-1820-51 Cyclone radial engines rated at 1200 hp for takeoff.

Maximum speed 292 mph at 25,000 feet.

Service ceiling 24,620 feet.

Maximum range 3101 miles.

Dimensions: Wingspan 103 feet 9 3/8 inches, length 67 feet 10.2 inches, height 15 feet 5 inches, wing area 1420 square feet.

Weights: 27,652 pounds empty, 37,997 pounds gross, 46,178 pounds maximum.

Armed with five 0.30-inch machine guns, with one gun in each of nose, dorsal, ventral, and two waist positions.

A maximum of eight 600 pound bombs could be carried in an internal bomb bay.