It seems F13 wasn’t used because of superstition. Instead, a YF-17 prototype (late 1960’s) lightweight fighter was designed to be cheaper than the F15 but lost out to the F16. So after a redesign, it became the F/A-18.


Peter Suciu writing in 19FortyFive makes the following points:

To reduce confusion, the US  Tri-Service aircraft designation system was introduced in 1962 as follows:

  • A - attack aircraft.
  • B - bomber.
  • C - cargo.
  • E - special electronic installation.
  • F – fighter.
  • K – tanker.
  • L - laser-equipped.
  • O – observation.
  • P - maritime patrol.
  • R- reconnaissance.
  • S - anti-submarine warfare.
  • T – trainer.
  • U – utility.
  • X -special research.

When developing the YF-20 Tigershark Northrop was offered the F-19 designation, but wanted an even number because so many Soviet aircraft had odd numbers!


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