The USAAC announced a competition in 1934 for a new multi-engined bomber with the requirement that it carry ~2000 lbs of bombs 2000+ miles at 200+ mph (with 250 mph preferred). The three entrants to the competition were famously the Douglas B-18, the Martin 186, and the Boeing Model 299, which would go on to become the B-17. The core difference in design taken by Boeing relative to the other two competitors came in the choice of the number of engines and thus the possible size of the aircraft that could be designed. Boeing decided to use 4 engines, allowing them to design a much larger aircraft that had higher range and bombload than the competing designs. Why did Douglas and Martin choose not to design 4-engined bombers for this competition?

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    $\begingroup$ According to Wikipedia "while the Boeing design was clearly superior, its four engines eliminated it from consideration and the crash of the prototype put its purchase on hold". Apparently Boeing built a prototype that was not in line with the requirements (it was twice as big as the other two!), basically betting that at a certain point during the war the Army would have needed it. Their bet was right. $\endgroup$
    – sophit
    Apr 6, 2023 at 8:29
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    $\begingroup$ Is your question "Why did Boeing choose to use 4-engines on the B-17?" or "Why did Douglas and Martin choose not to design 4-engined bombers for this competition?". They don't seem like the same question at all. $\endgroup$ Apr 6, 2023 at 13:59
  • $\begingroup$ Both questions. I think they are intertwined. Clearly the Boeing and Douglas engineers made a different technical choice and I think the question is understanding why each group made the choice they did. So understanding both the thoughts of the Boeing engineers and Douglas engineers is valuable. $\endgroup$ Apr 6, 2023 at 21:08

1 Answer 1


Martin actually did have a competing design, the twin boom XB-16 that went along with the Boeing XB-15 submitted for another USAAF requirement to travel 5000 miles.

Douglas, after their enormously successful DC-3, also had a 4 engine DC-4E airliner on the drawing board.

But Boeing was simply in the right place at the right time with proven experience that resulted in designs such as the 314 Clipper and not only the B-17 bomber, but also the 307 Stratoliner.

As it turned out, even though the Martin and Douglas designs were light years ahead of designs from the previous decade and as fast as contemporary fighters of the early 1930s, the decision to adopt the larger 4 engine Boeing aircraft as "heavy bombers" paid off in better defensive capability, larger payload, and longer range.

The two engine designs lived on as "medium bombers" better suited for shorter range tactical support missions.


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