The Boeing 720 was a modification of the Boeing 707. Why was it given the unusual number of "720" instead of a "707-xxx" or "7x7" designation?


Because the launch customer, United Airlines wanted it. From Boeing frontiers:

The 720 was a ... first marketed to the airlines as the model 707-020. United Airlines was very interested in the 707-020 but had previously decided to go with Douglas and the DC-8. To help United avoid any negative public relations for going back to the 707, Boeing changed the name of the 707-020 to the 720.

According to aviationweek, the name change was at the behest of William ‘Pat’ Patterson, the president of launch customer United Airlines.

  • 2
    $\begingroup$ You'd think it would be negative PR for Douglas, but these decisions don't need to be rational... $\endgroup$
    – OrangeDog
    Apr 14 '16 at 14:25
  • $\begingroup$ @OrangeDog I really doubt that a company cares about the PR results for another company that performed below expectations, which is why I assumed United moved away from Douglas. $\endgroup$
    – Nzall
    Apr 14 '16 at 15:26
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    $\begingroup$ @NateKerkhofs Exactly, it's not clear why Pat though that would be bad PR for United. $\endgroup$
    – OrangeDog
    Apr 14 '16 at 15:27
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    $\begingroup$ On second thought, I doubt it was like that at all. I bet it was more analogous to a new iPhone launch. We don't think of new airplane launches quite the same now, they are mostly about efficiency and so forth. In the sixties, airplanes were advancing with speeds rivaling Moore's law. Imagine Apple launching an iPhone 4, having a lackluster performance or availability problems, and switching back to a slightly modified iPhone 3. Would they want to call it an iPhone 3? Would that be good for PR/sales? $\endgroup$
    – wedstrom
    Apr 14 '16 at 16:20
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    $\begingroup$ @wedstrom continuing that digression, Intel's "Core" CPUs all trace their ancestry back to the Pentium Pro through Pentium 3 and not the Pentium 4, which turned out to be pretty much an evolutionary dead end. And yeah, in the process they re-branded and now "Pentium" is only used for low-end stuff. $\endgroup$
    – hobbs
    Apr 14 '16 at 18:49

The 720 first flew before the 727 project began. At that time, there was no "7x7 series" – just the 707.

(The 717 passenger plane didn't come along until the 1990s, though the internal Boeing model number of what are usually called the C-135 Stratolifter and KC-135 Stratotanker was also 717, and that did exist at the time the 720 was produced.)


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