Non-Standard DOD Aircraft Designations

Copyright © 2002-2023 Andreas Parsch

1 Introduction

2 Designations

3 Acknowledgements

1 Introduction

This article will show a few misapplications of the U.S. Joint Aircraft Designation System of 1962. I want to present and discuss the various thoughts about why the particular designations were assigned, and what designations would have been correct. Please note, that the list of non-standard designations is not intended to be complete. There are many more designations, which do not strictly follow the official rules and regulations. Especially the use of non-standard prefixes and suffixes has become standard ;-) in recent years! If your favorite "wrong" designation is not included, please drop me a line, and it will be added.

There are also numerous aircraft used by the U.S. armed services which do not use any official military designation at all, or worse yet, use a "pseudo-designation" which somehow looks like a real one (e.g. "MH-90" or "UC-880"). These undesignated aircraft are outside the scope of this article.

1.1 Allocation of Designations

The current regulations for allocating aircraft and missile designations, called MDS (Mission, Design, Series) designations, are defined by Air Force Instruction (AFI) 16-401. For a detailed explanation of the terms, definitions, and code letters of the MDS system, please refer to the article about Current Designations Of U.S. Military Aircraft on this site.

The procedure for allocation of an official MDS designator follows a lot of bureaucratic red tape, and is explained in detail in the article about Allocation of Official Aerospace Vehicle MDS Designations). The bottom line is that there is no "single point of blame" when an MDS is allocated which doesn't conform to the regulations.

1.2 Errors in Designations

While it probably can't be expected that the regulations are always followed to the letter, there have been some gross violations of them. I want to briefly summarize the various types of errors made in these "wrong" designations. The list of examples for each category is far from complete.

1) Some aircraft use non-standard or misleading basic and/or modified mission letter(s). Examples include: F/A-18, F/A-22, CC-130J, FB-111, F-117, AL-1, SR-71, TR-1 and EA-37B.

2) Several designations use out-of-sequence design numbers (e.g. A-37, B-21, KC-767, F-35, F-117, RU-38, T-6) or reuse previously assigned numbers (e.g. AV-8, RC-7B, KC-10, FV-12, OA-1K, EA-37B).

3) The series suffix letters are frequently not assigned alphabetically. Typical cases include special suffix letters for export versions of aircraft (e.g. UK variants usually use the suffix "K", as in C-130K or F-4K), or use of identical suffix letters for rather different variants (e.g. F-16C/D for all single/two-seaters of the F-16 despite significant changes). The use of "special" suffixes or dual letters, where a new series letter would have been appropriate, is also not uncommon (e.g. AV-8B+, F-16CJ). However, the latter are always unapproved semi-official designations.

4) Another frequent misapplication of the designation system is the allocation of several different basic (Mission-Design) designations to the same aircraft design. The most striking example is the Boeing 707. The designations C-18, C-137, E-3, E-6, E-7 (cancelled and replaced by EC-18), E-8 and T-49 all refer to modified 707s. All these designations are valid by themselves, but according to the regulations, only one basic designator (C-137, as it was the first) should have been used for the military Boeing 707. The Boeing 747 is similar with five different basic designators (C-19, C-25, C-33, E-4, L-1).

5) The opposite of the previous type of error can also be found, although not as often. Sometimes the same basic designation is used for rather different aircraft. Typical examples include the H-1 series, shared by the UH-1 and AH-1 helicopters, and the C-12J, which is a different type of aircraft (Beech 1900) than the other C-12s (Beech King Air 200).

2 Designations

2.1 Boeing (McDonnell Douglas/BAE) AV-8 Harrier

While the AV prefix is of course perfectly fine for the Harrier VTOL attack aircraft, the number 8 is not. The V-8 designator was originally allocated to the Ryan XV-8A Fleep, an experimental Army aircraft with some resemblance to today's "ultra-light" aircraft.

When the Harrier was selected for operational use by the U.S. Marines, it was originally designated as AV-6B. This was a logical designation, because the Harrier was a direct development of the Hawker-Siddeley Kestrel, which had been tested in the U.S. under the designation XV-6A. However, for unknown reasons, it was later decided to designate the Harrier in the attack series - the next available number was A-8. However, someone obviously was very "smart" ;-) and realized that the Harrier was still a VTOL aircraft, which are represented in the designation system by the "V" vehicle type symbol. So instead of A-8, it became the AV-8 ... and the fact that the next number in the V-series wasn't anywhere near 8 had been completely overlooked (or - more probable - ignored)!

The initial AV-6B was a logical choice, but if for some reason a new design number had been necessary, the Harrier should have become the AV-12 (the V-series had reached V-11 at the time). When later allocating a designation to a then proposed supersonic Harrier development, the Navy did a much better nomenclature finding job, and came up with the perfectly valid designation of AV-16A.

As a side note, available official documentation doesn't show any official reason for the redesignation. The official confirmation of the redesignation of AV-6B to AV-8A explicitly requested the cancellation of the XV-6A and XV-8A designations to avoid any further confusion. It also said that the AV-8A designation was orginally confirmed only orally, and adds that in the future the proper paths for MDS assignment and allocation should be used (implying that the oral confirmation was given prematurely) to avoid unnecessary confusion (thereby apparently referring to the reuse of the not-yet-cancelled V-8 designator).

It is possible that the U.S. Marine Corps wanted to avoid having both "A-6" and "AV-6" aircraft in the inventory. One interesting theory even says that AV-8 was chosen because it reads as "aviate" - certainly attractive for USMC aviators! A designation allocated just for pun :-)?

2.2 De Havilland RC-7B

The RC-7B is not a modified version of the de Havilland C-7A Caribou (DHC-4). Instead, the designation was assigned by the U.S. Army to the de Havilland Dash-7 modified as intelligence gathering aircraft for the ARL-M (Airborne Reconnaissance Low - Multimission) program. Apparently, someone in the Army just liked to assign the number "7" to the DASH-7 airframe.

Apart from the obvious problem, that the same basic designator (C-7) is now applied to two completely different aircraft, there are two more remarkable facts about this "mis-designation":

Available documentation shows that the Army requested an MDS for the ARL-M aircraft, and explicitly asked for an "RC-7" designation:

Although the remainder of the request clearly described the aircraft as a modified DHC-7, no reference whatsoever was made to the fact that "C-7" had been previously used for a different de Havilland aircraft. When the request was forwarded by the USAF Nomenclature Office to HQ USAF for approval, the following information was included:

It seems that someone at Nomenclature Office correctly determined that the next series letter in the C-7 series was "B", but did not realize that the C-7A was a different type of de Havilland aircraft than the DHC-7. This is the only explanation I can imagine for the description "C-7A modified ...". Interestingly, the number of engines was correctly given as "4" in this letter, but it finally ended up as "2" in DOD 4120.15-L (possibly because someone thought that a "modified C-7A" must have the same number of engines as the C-7A itself).

Update: On 15 August 2004, the designation EO-5C was officially allocated to the ARL-M aircraft. This is one of the rare cases where a non-conforming designation was officially replaced by a correct one.

2.3 Lockheed Martin CC-130J Hercules

Other than one would expect at first glance, the CC-130J is not the Canadian version of the C-130J Hercules. Instead it's the new USAF designation for the stretched variant of the C-130J, previously known as C-130J-30. The "CC" prefix is however not covered by the designation system. It would mean "a transport aircraft modified for the transport role", which doesn't make sense. As a side note, the suffix letter "J" for the modernized Hercules is also non-standard, because it's a reuse of a previously allocated suffix. The next proper suffix would have been C-130W (following EC-130V).

According to Lockheed Martin, the USAF could not use the C-130J-30 designation, because "the documentation structure within the Air Force cannot support a suffix such as -30". This appears strange, because such "block number" suffixes are widely used by the USAF, e.g. for the numerous F-16C/D variants. Anyway, whatever the exact reason is, the USAF apparently found out that they couldn't use the C-130J-30 designator. The Nomenclature Office actually proposed C-130W, and the C-130J Program Manager eventually agreed to that. However, for reasons unknown to me, HQ USAF/XPPE did not approve C-130W, and suggested CC-130J instead. It seems they wanted to keep the -130J suffix for the stretched version, and so the only way out was a modified mission prefix. As a matter of a fact, however, the stretched C-130J is a transport and nothing else, and therefore no other modified mission letter than "C-for-Transport" was applicable. This is about the only explanation for the CC prefix I can think of. As has been confirmed by Lockheed Martin, any CC-130Js modified for other missions will retain the second C to distinguish them from non-stretched C-130Js modified for a similar purpose. E.g., a search-and-rescue variant of the CC-130J would become the HCC-130J.

Update: On 5 January 2004, the CC-130J designation was changed to a plain C-130J in the DOD's official MDS designation table. Whether this is only a "paper change" or if the USAF will actually cease to use the CC-130J designator remains to be determined.

2.4 Boeing (McDonnell Douglas) F/A-18 Hornet

The origin of the Hornet's F/A-18 designation lies in the fact that originally two different versions were planned (F-18 and A-18), the capabilities of which were eventually combined in a single production version. The A-18 designation would have been out-of-sequence, and therefore non-standard, too.

Slashes or other "special characters" are not allowed in aicraft designators. In fact, the aircraft appears as FA-18 in DOD's designation listing (DOD 4120.15-L). "FA" is actually a valid prefix (attack aircraft, modified for fighter role), but the designation is now in the "A" series, and therefore out-of-sequence. It is interesting to note that the "F" modified mission letter was not included in the designation system until at least 1977. It is quite possible that its introduction coincides with the adoption of the FA-18 designation for the Hornet.

The Hornet should have simply retained the F-18 designation. The "F" designator explicitly includes fighters with ground-attack capability (otherwise, almost all fighters would have to be designated "AF"). If for any reason the ground-attack features had to be emphasized, an "AF" prefix could have been used.

Anyway, the actual reason for the "F/A" prefix is relatively simple - sort of. As soon as it had become clear that the air-to-air (Fighter) and air-to-ground (Attack) roles of the Hornet would be integrated into a single variant, the Naval "attack community" refused to a fly an F-designated aircraft, and vice versa. The "AF" prefix wasn't acceptable either, because to the "attackers", it still looked like no more than an adapted fighter (which it is, of course!), while the "fighters" complained that the "A" came first! As it turned out, the only "acceptable" designation prefix was "F/A".

It has also been argued that the new F/A-18E/F "Super Hornet" versions should have received a completely new design number (i.e. F/A-24A/B) because of the extensive changes. However, enlarged variants of aircraft with significantly larger internal volume but very similar overall appearance didn't always receive new basic designations in the past, either.

2.5 Lockheed Martin F-35

The F-35 designation for the Joint Strike Fighter is the latest in a line of out-of-sequence designations. What's new about this one is the history of its creation. On 26 October 2001, a press conference was held at the Pentagon to announce the winner of the JSF competition, held between the Boeing X-32 and the Lockheed Martin X-35. When the X-35 had been declared the winner, one of the questions asked was about the designation for the production JSF. USD ATL (Under Secretary of Defense for Acquisitions, Technology and Logistics) Edward C. "Pete" Aldridge mentioned the X-35 designator of the Lockheed Martin demonstrators, briefly exchanged a few words with his co-presenter, JSF Program Manager Major General Mike Hough, and then said it would be called "F-35". That's it. The transcript of the press conference can still be found here.

As it turned out, no designation whatsoever had been reserved, let alone approved, for the production JSF at that time, and Aldrigde and Hough - obviously not knowing much about the aircraft designation system used in their department - simply replaced the X by an F. Of course, just about everyone interested in the subject had expected the logical designation of F-24. In fact, Lockheed Martin had also expected this, and was reportedly a bit upset about the turn of events, apparently already having referred to the hoped-for production JSF in-house as the "F-24".

The official request for MDS designations for the three JSF variants was placed by the JSF Program Office on 17 December 2001. The paragraph requesting "F-35" said:

It was not before 16 April 2002 that the requests for F-35A, F-35B and F-35C (for the CTOL, STOVL and CV variants respectively) were forwarded by the USAF Nomenclature Office to HQ USAF/XPPE for approval. This is an unusually long delay, and may indicate that there was much discussion about the validity of the F-35 designation and/or the reasoning why it should be assigned (the latter boiling down to "It should be 'F-35' because some high-ranking but ill-informed official said so"). Nevertheless, the Nomenclature Office included the following paragraph in its letters (example for F-35A):

However, the recommendation was to no avail, and on 5 June 2002 HQ USAF confirmed the F-35 designations (without further commenting on the F-24/35 controversy).

Note: As of December 2006, the official USAF biography of Col. Joseph A. Lanni says that he has flown classified prototypes, and lists YF-24 among the types he has flown. It appears that the YF-24 designation has been used (semi-)officially for an as yet undisclosed aircraft. Since this YF-24 designation reportedly came into existence before 2001, it put the DOD into a dilemma when designating the JSF: Either use F-24, and confuse anyone who is cleared to know about the secret YF-24, or use F-25, and be flooded by questions about F-24 (the whole "F-19 game" again)! So the apparently "accidental" selection of F-35 for the JSF would have been an easy way out. After all, the public was already used to the assignment of out-of-sequence numbers for all kinds of reasons.

2.6 General Dynamics FB-111 Aardvark

This strategic bomber version of the F-111 should have been the BF-111 - a fighter, modified for strategic bombing (there is currently no "B" modified mission letter, but there is no reason not to introduce it). I haven't found any source suggesting an explanation for this wrong designation. Maybe SAC just refused to fly its bombing missions in an aircraft with a basic "fighter" designation ;-). Also, "FB" can be conveniently read as "fighter-bomber".

2.7 Lockheed Martin F-117 Nighthawk

This is probably the best known "illegal" designation of them all! Both the type letter "F" and the number 117 of the Nighthawk's designation don't conform to the regulations in the designation system.

Why "F"?

Although it is commonly called the Stealth Fighter, The Nighthawk should have received an "A" designation. It has no air-to-air role whatsoever, and the "A-for-Attack" designator is in fact prefectly made for tactical ground-attack aircraft like the F-117. The topic has been discussed to death among enthusiasts, but there seem to be essentially two possible reasons for the assignment of an F-designation:

Why "117"?

Although not officially acknowledged, it is known that aircraft (mostly Soviet/Russian ones, but also including U.S. "black" prototypes) used in secret testing at Groom Lake or Tonopah AFB have designations assigned that look like continuations of the pre-1962 "century series" designators (see article on Cover Designations for Classified USAF Aircraft). Examples given include YF-110 for MiG-21s and YF-113 for MiG-23s. Suffix letters (as in YF-113E or YF-113G) are also used. The YF-113G designator actually refers to a completely different aircraft type (most likely a U.S.-built testbed) than YF-113 designations with other suffixes. It is de facto known that all of these "designations" use a "YF" prefix (for simplicity and/or secrecy), even if they don't refer to fighter aircraft. By far the most plausible theory about the Nighthawk's designation says that the aircraft (then known as SENIOR TREND) acquired the YF-117A designation in this scheme. When the aircraft was prepared for operational service, flight manuals etc. had to be printed, and these were labeled with F-117A, either on purpose or because of some intra-service communication problem. Because nobody wanted to re-label all documentation and manuals for the aircraft, the designation was kept even after the Nighthawk went public.

As to why exactly "117" (and not, say, 116 or 118) was selected for the SENIOR TREND aircraft, no really convincing ideas have come forward. In fact, all evidence points to an arbitrarily selected number - one number is as good as the other. It should be noted that the SENIOR TREND hadn't reserved the 117 for exclusive use - the Northrop TACIT BLUE aircraft was designated YF-117D.

Why no "F-19"?

Independent from the question, why the number 117 was allocated to the Nighthawk, there was much speculation about the missing designation F-19. For a long time, the only known fact was that F-19 was never officially allocated to any unclassified aircraft project. But since some time, we know that the designation F-19 was definitely skipped. The reasons are documented in the F-19 section in the article about missing USAF/DOD aircraft designations.


If one puts everything together, the only "valid" designation for Lockheed's stealth fighter would have been A-11A. The fact that this designation has been reserved, but apparently not used, in the 1986/88 time frame is an interesting factoid in this context.

2.8 Boeing AL-1

AL-1A is the designation for the planned ABL ("Airborne Laser") aircraft, a Boeing 747 equipped with a high-power laser to intercept and destroy ballistic missiles. The designation has several flaws.

First, the "L-for-Laser" basic mission prefix was introduced just for this aircraft. While the addition of new letters is nothing to object to, a mission letter based on the type of weapon used by an aircraft is grossly against the original purpose of the designation system. Before "L" all prefix letters described the mission (or vehicle type) of an aircraft regardless of the equipment used to fulfill this mission. Nobody would have considered designating, say, nuclear capable aircraft with an "N" designator, yet an equivalent thing was now done for laser-equipped aircraft.

It seems that the ABL was considered as such a "revolutionary" weapon that only a new "special" designation would do. The original letter which initiated MDS assignment for the aircraft, dated 15 April 1996, includes the paragraph:

While the rules were simply bent to allow for the "L" prefix, the "A" modified mission letter is just another misapplication. "A" is defined as "Ground Attack", something which the ABL will never do. The "AL" prefix was probably chosen because it can be conveniently read as "Airborne Laser" or "Attack Laser" (another name sometimes used for the aircraft). However, designation prefixes were never meant to be acronyms (a similar error was made when the ASAT missile prototype was designated as ASM-135 (ASM = Anti-Satellite Missile), when AIM-135 would have been appropriate). The correct prefix would have been "F", which is explicitly defined as applicable to aircraft designed to intercept and destroy other aircraft or missiles. This is exactly the mission of the ABL.

The correct designation for the AL-1 would have consisted of an existing basic designation for the Boeing 747, prefixed by an "F" modified mission letter. There have been several basic designations assigned to the 747 (thereby also violating the regulations), but the most applicable would be the two non-cancelled ones, E-4 (used for E-4A, E-4B) and C-25 (used for VC-25A). Therefore the ABL should have been designated as either FE-4C or FC-25B. I admit that both of these designations look rather unusual with their "F-for-Fighter" prefix, but they are in perfect agreement with the designation system as defined. It is interesting to note that the designation YFC-36A was reserved by the USAF Nomenclature Office in spring 1996 for a "four-engined" (no other details available) Air Force aircraft. While I cannot definitely confirm this, the "YFC" prefix of this designation strongly suggests that it was tentatively reserved for the ABL in case the new L-for-Laser mission designator would not be approved.

2.9 Lockheed SR-71

The SR-71 designator is actually a continuation of the pre-1962 bomber series, which ended with the B-70 Valkyrie. Late in its career, the B-70 was proposed for the reconnaissance/strike role, with an RS-70 designation. The "RS" prefix (sometimes written as "R/S") was actually allowed as an explicit "special case" in the orignal 1962 issue of the designation regulations. When it was clear that Lockheed's A-12 aircraft (then used by the CIA) had much greater performance potential, it was decided to "push" a USAF version of that one instead of the RS-70. This USAF version was to become the RS-71.

"Conventional" wisdom now says that then president Lyndon B. Johnson messed up the designation in his public announcement and called it the SR-71 - and nobody wanted to correct the president. Because the strike mission had been cancelled anyway, "SR" was quickly reinterpreted as "Strategic Reconnaissance". However, a first-hand witness of those events recently revealed in Aviation Week & Space Technology, that LBJ did not misread anything. In fact, then USAF Chief of Staff LeMay simply didn't like the "RS" designator - he already objected it when the RS-70 was discussed, preferring "SR-70". When the RS-71 was to be announced, he wanted to make sure it would be called SR-71 instead. He managed to have LBJ's speech script altered to show "SR-71" in all places. Using archived copies of LBJ's speech, it can actually be verified that it reads SR-71 both in the script and on the tape recording. However, the official transcript of the speech, created from the stenographic records and handed to the press afterwards, shows "RS-71" in three places. It seems that not the president but a stenographer did accidentally switch the letters, and thus create a famous aviation "urban legend".

Anyway, the correct designation for the SR-71 would have been simply R-1A. There is an R-for-Reconnaissance mission letter in the designation system and it doesn't make any distinction between strategic, tactical or other reconnaissance.

2.10 Lockheed TR-1

The second production batch of the U-2R was initially designated TR-1A (and TR-1B for the two-seat trainer). This was purely for political reasons, to emphasize the reconnaissance role of the aircraft. While the "R" primary mission letter and the design number 1 are text book examples for correct use of the designation system, the "T" prefix letter is not! In the TR-1, it stands for "Tactical", apparently to contrast it from the "SR - Strategic Reconnaissance" designator of the SR-71. In 1991, when the Cold War and the need for such "diplomatically correct" designations had ended, the TR-1A/B was redesignated as U-2R/TU-2R.

Note: The NASA used a version of the TR-1A/U-2R for environmental reconnaissance work, calling the aircraft "ER-2". This was not a military designation, and does not fit into the "R-2" slot of the R-series (which has, so far, only the non-standard members TR-1 and SR-71). The TR-3A designation, which was rumoured to be allocated to a secret stealth battlefield surveillance platform (which almost certainly doesn't exist), is purely fictitious.

2.11 Boeing KC-767

In September 2002, KC-767A was officially approved as the designation for the projected Boeing 767 tanker conversions to be leased by the U.S. Air Force. Instead of using the next number in the C-series and designating the aircraft as KC-42A, the manufacturer's design number was used.

The MDS request from the CDARA (Commercial Derivative Air Refuelling Aircraft) program office to the USAF Nomenclature Office, dated 6 August 2002, says:

As usual (nowadays), the Nomenclature Office stated their objection when forwarding the request to HQ USAF, and included the paragraph:

Also as usual, HQ USAF/XPPE ignored the objection, and confirmed the KC-767A designation on 18 September 2002 with the words:

The special reference to the "approving authority for MDS designators" is unusual for these confirmation memos, and may indicate that XPPE wanted to make clear just who is the boss on all MDS issues ;-).

3 Acknowledgements

I would like to thank the following people who helped to write this article:

Comments and corrections to: Andreas Parsch

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Last Updated: 28 November 2023