The Boeing B-17 Flying Fortress and the Consolidated B-24 were the United States' two standard heavy bombers until the arrival of the Boeing B-29 Superfortress in 1944. The B-17 served in almost every theater of World War II, but it used mostly by the US Eighth Air Force, based in the UK, to bombard German targets. The first missions were in daylight hours to improve accuracy, but this strategy plus a lack of adequate fighter coverage, resulted in very heavy losses of aircraft and crew. Its first bombing mission was with the RAF as Fortress Is, but it was hardly ready for war. As refinements progressed, along with better pilot training and tactics, it became a formidable weapon in the Allied war against Germany.
The Flying Fortress was designed in response to a USAAC competition, announced on August 6, 1934, to find a modern replacement for the assorted twin-engine Keystone biplane bombers and greater performance than the Martin B-10. While the performance of the B-10 was considered adequate at the time, the Keystones lumbered along at about 115 mph (185 km/h), were very unmaneuverable, lightly armed and carried only a limited bomb load.1 The requirement was for a multi-engine bomber to be used for coastal-defense.
Specifications required were:
• Range of at least 1,020 miles (1,640 km).
• Speed of 200 to 250 mph (322 to 402 km/h).
• Bomb load of 2,000 lb (907 kg).2
A Boeing design team began work on the Model 299 prototype in June 1934 and construction began in August of the same year. The most significant rival to the Model 299 was the Douglas DB-1, which was based on the Douglas DC-2. The third competitor was the Martin 146.
The 299 would be built at Boeing’s expense and there would be no reimbursement if it did not win a contract. After Boeing failed to win a contract to produce the Boeing B-9, the Model 299 was a make-or-break gamble for Boeing.3
The B-17 (Model 299) was a cross between the Boeing 247 passenger airliner and the experimental XB-15 (Model 294). The B-17 prototype used some of the same construction techniques as the Boeing 247. It was a semi-monocoque all-aluminum fuselage and the pilot and copilot sat side-by-side in a conventional cockpit. It was powered by four 750 hp Pratt & Whitney R-1690 Hornets. The XB-15 was a larger version of the B-17, but it was considered experimental.