a reply to: CrownCartwheelCreed
You are making the same mistake that spaceman42 made in thinking that there is a linear progression in these designations. That is not the case.
The practice of using non-standard mission/design/series (MDS) designations began with Project HAVE DOUGHNUT in 1968. The project pilots were trying
to figure out how to log their flight time in the AF Form 5 and Navy flight records. For security reasons, they obviously couldn't list the airplane
as a MiG-21. The solution was to use a designation that had not been previously used, and would never be assigned to a production aircraft. The
"Century Series" designations (F-100 and beyond) had been phased out in 1962, and only one designation was needed for the project. They picked YF-110B
since YF-110A had been briefly used to designate the Air Force version of the F4H-1 before it was formally designated F-4C under the new standardized
Now, a lot of people would like to draw a straight line between the YF-110B and the YF-117A with all the known and missing designations in a neat row,
but it didn't work that way. The numbers were not assigned in any linear or logical order. In 1969, two MiG-17F aircraft were acquired for evaluation
purposes. Although the two airplanes were physically identical and were sometimes even flown together on dual sorties, they each received separate
designations and project names. The HAVE DRILL project aircraft was designated YF-113A. Because the AF Form 5, at that time, did not accommodate tail
numbers, the HAVE FERRY project aircraft was designated YF-114C.
In 1970, a borrowed Chinese-built MiG-17F (J-5) was flown at Phu Cat Air Base, Vietnam, with the designation YF-113C. This designation was recycled in
the early 1990s for a completely different aircraft.
In 1970, the YF-114C was joined by a MiG-17PF (designated YF-114D), and several MiG-21s. Since, by this time the AF Form 5 had been modified to
accommodate tail numbers, the MiG-21s were all designated YF-110B.
The Red Hats pilots who fly these planes refer to the aircraft as "classified prototypes." Although they are not true prototypes, the airplanes are
used for experimental and developmental testing (the latter being more along the lines of operational test and evaluation). Non-standard designations
were also applied advanced technology demonstrators and full-scale development prototypes of domestic manufacture (YF-117A (Senior Trend), YF-117D
(Tacit Blue), YF-118G (Bird of Prey), etc.). Recently, a few two-digit designations have surfaced, as well.
Again, these numbers are not assigned in a linear progression and any "missing suffixes" are usually just those that were never used (or not yet