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1. In 1961 the Army also evaluated the Northrop N-156 and Fiat G.91 as possible FAC/tactical reconnaissance aircraft. USAF determination in insisting that it should operate such aircraft in support of the Army caused the cancellation of further testing.

2. The DoD designation system dictates that the AV-8 should have a designation in the "V"-series, with "A" as a modified mission symbol. However, it is incorrectly placed in the "A"-series as A-8 with "V" as the aircraft type symbol. Recent research by Andreas Parsch indicates that the DoD assigned the designation AV-6B to the aircraft in 1970. Judging from the fact that the same description for the aircraft was seen for the AV-8A designation in 1974, it seems that initially at least the correct designation (AV-6B) was assigned.

3. There is some confusion regarding the designations of A-11 and A-12 as they relate to the Blackbird. The popular explanation is that Lockheed assigned the designation A-1 to the first preliminary design of the Blackbird, and continued in sequence with new designs until the final prototype, the A-12. However, in some documents the aircraft is referred to as the A-11, and Kelly Johnson himself is said to have referred to the aircraft as the A-11. In addition, when President Johnson publicly revealed the existence of the Blackbird, he referred to it as the A-11. Some sources suggest that this was a slip of the tongue, but in any case, both designations are non-standard. The Blackbird was not even considered as an attack aircraft until much later (in the form of the B-71), and both A-11 and A-12 are not in keeping with the chronological assignment of other numbers of that era in the "A" series. Finally, the A-12 was subsequently assigned to the A-12 ATA, precluding the possibility that the A-12 was a standard designation.

4. The Blackbird's original designations (A-11 or A-12 or both - see note 3) are both non-standard. This leaves the A-11 designation unassigned in the the Joint DoD designation system of 1962.

5. Because the Martin B-26 was out of service in 1948, there was no designation conflict when the Douglas A-26 was redesignated to B-26; this was obviously done to keep the number "26" associated with the aircraft. Although technically no conflict existed between the two aircraft, the repetition of the designation causes some confusion.

6. B-61 - B-68 (excluding B-66) are missiles and were later redesignated as such.

7. B-72 - B-87 are missiles and were later redesignated as such.

8. The name "Yic" came from the prototype designation of the aircraft, Y1C-24.

9. The F-19 designation is rumored to have been skipped in order to promote the F-20 as a "new generation" fighter. This has since been confirmed by Andreas Parsch through an FOIA request to the DoD. Apparently, Northrop requested the number "20" versus "19" to avoid a confusion with the MiG-19, which may sound a little unusual, but is apparently the case. See Andreas Parch's excellent summary of "unknown designations" for a more complete explanation. The F-19 was earlier assumed to be the designation for the Lockheed Stealth Fighter, now properly known as the F-117A. By skipping the F-19 designation, the U.S. was able to truthfully deny any knowledge of an "F-19 Stealth Fighter." (See note 12 for possible explanations of the F-117 designation)

10. F-98 and F-99 are missiles and were later redesignated as such.

11. The F-101B was originally designated the F-109, but was later dropped. The designation was subsequently reassigned to the experimental F-109 VTOL interceptor.

12. There are several theories as to the designations F-112 through F-116 as a result of the Stealth fighter's designation of F-117. Once again, Andreas Parsch has come up with an answer that is more plausible than some of the earlier theories put forth. I'll leave those theories intact in this note, but for now will reprint Andreas' e-mail regarding his findings:

an "informed source"[*] has provided me with some information about the 
allocation of "pseudo-designations" to aircraft tested secretly by the U.S. 
Air Force.

[*] I know that "informed source" does sound dubious. However, he told me 
his name and mentioned a few other people involved, but has asked not to be 
identified in any public message. The background about how and where he 
obtained the information constitutes a coherent, and in principle 
verifiable, story. It also explains the lack of information regarding the 
actual aircraft types which used the various YF numbers.

These designations, as well as (fake) serial numbers were assigned for the 
purpose of creating USAF standard flight logs. The time frame of the 
information is late 1970's, and involves (at least) the 6513th Test Squadron 
"Red Hats". The following is a (probably incomplete) list of designations, 
together with bogus serial numbers, where available:

Designation             Serial Numbers
YF-110B                 75-001, 75-004, 75-010
YF-114D                 75-008

The omission of a suffix on the "YF-113" is intentional. FWIW, the original 
(real) serials 75-001 though -016 were all cancelled allocations.

Best wishes
As for previous ideas and rumors, one theory holds that the designations F-112 - F-116 are assigned to aircraft based at the USAF's Soviet aircraft squadron stationed at Nellis, possibly at the Tonopah Test Range (TTR) where the F-117 was being developed. However, another theory postulates that many test flights operating out of Nellis AFB, including those of acquired Soviet MiG aircraft, used the arbitrary call sign "117" and that it was used so often that Lockheed assigned it to the Stealth fighter to disguise its identity. In using the same call sign as that of other test aircraft, the stealth fighter would then be thought of as another secret aircraft of the MiG squadron by anyone hearing its designation and not an operational aircraft. A more outlandish scheme claims that after the 1962 designation system change, new fighters were "recessively" assigned designations following the F-111, the last fighter to have a pre-1962 designation. Therefore, it would be F-112 (F-14) Tomcat, F-113 (F-15) Eagle, F-114 (F-16) Fighting Falcon, F-115 (YF-17) Cobra, and F/A-116 (F/A-18) Hornet, leading up to the F-117 Stealth fighter. There is, however, a major flaw to this notion. If the new 1962 system were ignored and a "recessive" continuation of the pre-1962 system maintained, the Navy would presumably have kept its old system intact, so it would be F13F Tomcat, F-112 Eagle, F-113 Fighting Falcon, F-114 Cobra, and F5H Hornet, leaving open F-115 and F-116. However, most accounts totally ignore the F-5 and the YF-12 Blackbird prototype which flew in 1964; adding in these two aircraft could fix the flaw in this "recessive" theory, but the whole idea seems too bizarre. I also received an e-mail with a different version of this "recessive" theory (thanks to William Blake!): F-112 is the F-5 Tiger II, F-113 is the F-15 Eagle, F-114 is the F-16 Fighting Falcon, F-115 is the F-17 Cobra, F-116 is a classified aircraft, bringing us to the F-117 Nighthawk. This does, however, ignore the YF-12 Blackbird.

13. Helicopter designations in the new DoD system have been haphazardly assigned at best since 1962, with some following numerically from H-46 to H-67, but with others assigned designations from H-1 to H-8. No explanation is apparent at this time.

14. The USAF TTTS T-1A was named Jayhawk after the naming of the HH-60J, causing some inter-service rivalry over the name.

15. The P-73 & P-74 designations were skipped to give the Fisher Eagle "a good symbolic number", allegedly because the manufacturer wanted to associate the aircraft with the French 75 cannon of World War I fame.

16. It is of note that the R#V series continues from the Lockheed R#O series with the R6O/R6V as an overlapping transition.

17. There has been an apocryphal story that President Johnson misreported the designation RS-71 as SR-71, so the USAF kept it that way in order to avoid embarrassment on his part. Its mission description was correspondingly altered from "reconaissance-strike" to "strategic reconaissance". Both designations are non-standard, but the "-71" obviously came from the B-71, a proposed bomber variant of the [Y]F-12. The story about President Johnson has since been refuted (thanks to Jeff Rankin-Lowe and the Military_Aircraft_Designations mailing list!). Apparently USAF Chief of Staff LeMay simply liked SR-71 better than RS-71 and had LBJ's speech altered as such.

18. While the BT-2 design was being developed, Northrop became Douglas-El Segundo. Hence the designation became SBD and not SBT.

19. Why the DoD decided to follow the T-48 with T-1 (Jayhawk) rather than T-49 is a mystery. It now appears that all new trainers are being assigned numbers after the T-1, with the Slingsby T-3 Firefly and T-6 Texan II as examples, but so far with the T-2, T-4, and T-5 designations unassigned.

20. The "PT"-series continues in the Air Force designation of 1948 with the T-28.

21. When the F-111 was modified to act in the strategic attack role, the "B" modified mission symbol should have been placed before the "F," not after. The correct designation would then be the BF-111, not FB-111.

22. Upon the conversion of the T-37 to an attack role in 1963, it was correctly issued the designation of AT-37. It was tested and decided not to produce the aircraft, so it was relegated to a museum in 1964. However, in 1966 after the need for COIN was found in the Vietnam War was obvious, it was decided to produce the COIN variant of the T-37. The new variant was designated YA-37A, obviously just as a matter of convenience or association with the T-37. Technically, however, the aircraft should have been assigned a wholly new designation in the attack series, with "A" indicating that attack was now the new, basic mission. In that case, however, it should not have retained the number "37," and should instead have been assigned a chronological number in the "A" series, most likely A-7.

23. The A-1 designation was apparently skipped in the attack series beginning in 1926 to avoid confusion with the Cox-Klemin ambulance aircraft. Although there was a Fokker A-2 ambulance aircraft as well, it was out of service by the time the A-2 designation was assigned to the Douglas A-2 attack aircraft.

24. The F-22 designation was almost assigned to the F-15 STOL Maneuvering Technology Demonstrator, but was instead assigned the designation NF-15B.

25. One source suggests that the AP-2 was also operated by the Army and that the AP-2 designation was used rather than RP-2 to disguise its reconaissance mission, and thus avoid any "turf wars" with the USAF. The author cannot recall in which source this was located to verify this claim, however.

26. A FOIA request by Andreas Parsch yielded some more information on the H-36, H-38, and H-44 designations. Although most sources attributed H-36 and H-38 as reserved for the U.S. Navy, there was no information at all for the H-44. According to Andreas' request, on June 1, 1959, an Air Force letter was issued for H-36 for project "Long Ears" with an additional statement, "it is not desired to reveal any further information on the nature of these projects." The same letter also revealed that the H-38 designation was assigned to project "Short Tail" and the H-44 designation was assigned to project "Big Tom." As Andreas points out, it is unusual that these three, non-sequential, numbers were allocated at the same time. However, he offers an explanation. The designations H-36 and H-37 were skipped in the early 1950's by the U.S. Navy, which is probably why most sources attributed those designations to the Navy. Assuming that at the time the letter was issued (6/1/59) that the last Air Force "H" designation used was H-43, then it would make some sense for the Air Force to allocate two unused designations (H-36 and H-38) as well as the next chronological designation (H-44). 27. The skipping of the P-1 designation in the 1962 Joint designation scheme was most likely due to the fact that it was convenient to redesignate the P2V, P3V, P4Y, and P5M to P-2, P-3, P-4, and P-5, respectively. 28. Similar to note 27, the S-1 designation was most likely skipped out of the convenience of renaming the S2F to S-2 and continuing from there. 29. The T-4 and T-5 designations were skipped so that the the new JPATS trainer could have the T-6 "Texan II" designation, a reference to the classic T-6 Trainer. 30. Per Andreas Parsch's excellent website, the USAF "introduced the Q category for drones in 1947. Existing PQ models were redesignated. While no new OQ-numbers were assigned, existing OQ drones retained their designations." The Q-3 designation is a bit of an anomaly, as one source reports that (contrary to the rest of the Q designations) OQ-3 was redesignated to Q-3. Other sources claim that the Q-3 is merely a different version of the Q-1/ 31. Again according to Andreas Parsch's site, the Q-6, Q-7, and Q-11 designations may or may not have been assigned, since the OQ-6, OQ-7, and OQ-11 aircraft were still in use. 32. A FOIA request by Andreas Parsch did not yield any information as to why the number "39" was skipped.

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