The Boeing B-17B of 1939. After extensive testing of the service test airplanes, ten B-17Bs such as shown here were ordered in 1937 for delivery in 1939 and 1940. Differing only in minor detail from the Y1B-17A, the "B" featured a redesigned nose with a flat panel for the bombardier, and the elimination of a notch under the forward section. Also fitted were a navigator's blister above the cockpit, and constant speed full-feathering propellers. Power of the Wright Cyclone engines was also increased to 1,200 hp and gross weight increased to 46,000 lbs. A total of 39 airplanes of this model were built.