The heavily armored B-17F was distinguished by its molded plexiglass nose assembly and wide paddle-blade propellers. It could fly farther than previous B-17s because of the 1,000 gallons of additional fuel stored in self-sealing tanks. Under the Boeing-Douglas-Vega nationwide, collaborative production effort, Boeing built 2,300 B-17Fs, Douglas 600; and Lockheed (Vega), 500.