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Exceptions to the Tri-Service System

- question from name withheld

As previously discussed, the Tri-Service System was adopted by the Army, Air Force, and Navy/Marine Corps to provide a common, simpler naming convention for both aircraft and weapons. However, the system has not always been faithfully applied and the two cases you mention represent only a sample of the inconsistencies.

The first case that you mention is the F-19. At least officially, there never was any aircraft designated as the F-19, but there have been persistent rumors that this designation was given to some sort of secret stealth fighter that still remains classified. Or perhaps the designation was set aside for some secret fighter development program that was later cancelled. Another possibility is that the number was purposefully skipped to confuse potential adversaries like the Soviet Union and convince them to waste resources spying on some secret program that never actually existed. A more down-to-earth explanation is that Northrop requested the designation F-20 for its radically updated variant of the F-5 in order to make the aircraft seem more revolutionary. When the F-20 designation was approved by the Air Force, F-19 was skipped. The only other designation previoulsy skipped in the fighter series was F-13, but this is thought to be due to the military's somewhat superstitious nature and the perception that 13 is unlucky.

As for the F-35, the explanation is far less mysterious. The two prototypes developed under the Joint Strike Fighter program were the Boeing X-32 and Lockheed Martin X-35. These aircraft were numbered under the Experimental X-plane series rather than as fighters. However, it was decided at some point that the winner of the JSF contract would be designated by the X-plane number rather than renumbered under the fighter series. Thus, the winning X-35 demonstrator became the F-35 fighter as opposed to being redesignated the F-24, which would have been the next available value. While F-24 might have been a more logical choice, who are we to argue with the Pentagon.

Some other examples of illogical aircraft designations include:

F/A-18 Hornet: When originally proposed, the Hornet was to have been built in two versions, a Navy fighter (F-18) and a Marine Corps attack plane (A-18). If adopted, this Marine designation would also have been unusual since the next available position in the Attack series was A-12. Nonetheless, it was later decided that the two missions could be merged into a single multi-purpose aircraft, and the resulting design was christened the F/A-18. What is odd is that the F-16 and even recent upgraded versions of the F-15 and F-14 are also multi-purpose fighter and attack aircraft, yet none of them were ever given F/A designations. At most, a true application of the Tri-Service System would suggest that the basic model should be called the F-18 and a specialized attack variant called the AF-18, which itself would be atypical. A further interesting note is that the Tri-Service system specifially forbades the use of slashes or other special charcters in aircraft designations, and the Hornet is actually listed as the FA-18 in official DOD documents. In actual operational usage, we all refer to the plane as the F-18 and consider the F/A designation to be nothing more than a poorly thought out curiosity. Some have also argued that the new F/A-18E/F Super Hornet is sufficiently different from the earlier models to warrant a new designation of its own, the F-24 being the next available choice.

F-117 Nighthawk: Perhaps one of the most well-known examples of unusual designations is the F-117 stealth "fighter," which in actuality is not a fighter by any stretch of the imagination. The aircraft is actually a precision strike plane best designated as an attack aircraft or perhaps a bomber. Some sources suggest that Air Force brass, dominated by ex-fighter pilots, couldn't stand the idea that the service's most advanced plane of the time would be designated as anything other than a fighter. In addition, it has always been a mystery as to why the number 117 was chosen since this does not correspond to the current fighter series. It is actually a better fit in the pre-1962 series, which featured aircraft such as the F-100 Super Sabre, F-106 Delta Dart, and F-111. The prevailing theory is that this digit was chosen to help maintain secrecy, especially since F-112 through F-116 are thought to have been applied to Soviet aircraft acquired and tested by the US military. Perhaps it was hoped that anyone who stumbed upon the designation F-117 would assume that this too was a captured foreign plane.

AV-8 Harrier: While the designation AV is correct (V stands for vertical or short takeoff and landing, A for attack), the curious fact is that the Harrier seems to have adopted the number 8 in the A series rather than the next available value in the V series. V-8 had actually already been applied to the Ryan XV-8A Fleep, an experimental ultra-light vehicle evaluated by the Army. While A-8 would have been an acceptable and logical designation, the VTOL capabilites of the plane probably make it a better fit in the V series, in which case AV-14 would have been a more reasonable choice (V-13 was also available, but would have likely been skipped as previously discussed). The AV-6 might even have been acceptable since the Hawker-Siddeley Kestrel, a research plane that led to the Harrier, had been evaluated in the US under the designation XV-6A. Perhaps the cutest explanation for the AV-8 designation is that some clever Marine Corps officer realized that it sounded like "aviate." And that's probably the only time I'll ever be able to use "Marine Corps" and "cute" in the same sentence!

RC-7B ARL-M: The designation C-7 had been applied to the DeHavilland Canada DHC-4, a turboprop-powered cargo plane. However, the RC-7B is a completely different aircraft, a DHC-7. It is quite unusual for two different aircraft to be given the same basic designation. In addition, earlier versions of the RC-7B had been designated as the O-5A and EO-5B, so why this particular model was not designated the RO-5C, for example, is even more peculiar.

FB-111: Although the F-111 has never been operated as a fighter, the aircraft was originally seen as a multi-role attack fighter performing tactical bombing missions for the Air Force and air superiorty duties for the Navy. When a further strategic bombing variant was designed for the Strategic Air Command (SAC), it should've been designated as the F-111_ where _ would be the next available suffix letter, or perhaps as the BF-111 indicating a fighter modified for bombing duties. However, the FB-111 designation is technically invalid under the designation system.

SR-71 Blackbird: This designation is unusual on many counts, expecially when it is realized that it was originally intended to be the RS-71 or even R/S-71 standing for Reconnaissance and Surveillance. While S typically stands for Anti-Submarine, this special case was explicitly allowed in the original 1962 Tri-Service agreement. Nevertheless, the number 71 is also strange and appears to come from the pre-1962 bomber series which ended at the B-70. The most likely explanation is that a reconnaissance version of the B-70 was proposed as the RS-70, and the RS-71 followed suit. Now comes the interesting part--how the RS-71 became the SR-71. It has long been thought that the change in designation was the result of a mistake by Pres. Lyndon Johnson when he announced the existence of the plane. Supposedly he had inadvertantly reversed the two letters in a speech, and the new designation became official because no one wanted to embarrass the president. However, it has since been revealed that USAF Chief of Staff Curtis LeMay purposefully changed the designation in the president's speech because he preferred the designation SR-71 and wanted to ensure that that's how the plane would be known. Having pulled off his devious ploy, the SR was quickly explained away as standing for Strategic Reconnaissance. In a true application of the Tri-Service system, the aircraft should have been designated simply as the R-1A.

AL-1: The AL-1A is the designation being given to the Airborne Laser project, a Boeing 747 fitted with a high-power laser designed to destroy ballistic missiles. For starters, there is no provision for an "L" in the basic mission section of the Tri-Service System. The designation was created purely for this aircraft since it is equipped with a laser. Second, the "A" is also incorrect since the aircraft is not designed for ground attack. The designation was obviously intended to stand for "Airborne Laser" even though this clearly violates the basic purpose of the Tri-Service System. Since the basic aircraft is a 747 which already holds two basic mission designations, (which in itself is a further violation of the naming convention), the most correct decision would have been to adopt one of these and modify it for the new mission. Therefore, the AL-1 should instead be either the _E-4 or _C-25 where _ would be the most applicable modified mission prefix. "L" is already in use, standing for an aircraft modified for use in cold weather, so perhaps some other letter should have been adopted to stand for an "aircraft equipped with high-energy weapononry."

CC-130J Hercules: No, the CC-130J is not a Canadian model of the C-130J, following the examples of such aircraft as the CF-18 or CF-100. This is the designation applied a stretched model of the C-130J for the US Air Force previously known as the C-130J-30. The "CC" designation was supposedly selected because the -30 suffix was not supportable within the Air Force's documentation system. Apparently adopting a new suffix letter (C-130K, for example) was not acceptable and the only choice left was a new modified mission letter. But since the C-130J-30 is still only a cargo transport, the only modified mission letter that made any sense was "C." Thus, the aircraft became the CC-130J indicating "a transport aircraft modified for the transport role." But this is probably only the latest example of the many odd designations applied to the long-lived venerable C-130 design.

TR-1: Originally known as the U-2R, this improved model of the U-2 spy plane was re-designated as the TR-1 to represent its "tactical reconnaissance" role. While the R-1 is perfectly acceptable, the T modified mission designation is not since "T" stands for trainer. It is interesting that at the conclusion of the Cold War, the TR-1 designation was dropped and the aircraft were again designated as the U-2R.

A-37 Dragonfly: The Cessna A-37 was a light attack development of the T-37 Tweet, a two-seat jet trainer. When Cessna developed this attack variant of the aircraft, the "A" designation for attack was simply substituted in place of the "T" for trainer. In keeping with the Tri-Service system, the aircraft should have been dubbed the AT-37, a "trainer modified for the attack role." Or if the new aircraft had been considered so different from the original that it deserved its own basic mission designation, it should have been given the next available digit in the Attack aircraft series.

There is also a great deal of confusion in the Trainer series which was not restarted in 1962 but continued to number new planes consecutively under the pre-1962 system until at least the late 1980s. The only exceptions were the Lockeed T-1 SeaStar, a designation applied to a Navy version of the T-33, and the North American T-2 Buckeye. Yet inexplicably, the Trainer series was restrated in the 1990s with the introduction of the Beech T-1 Jayhawk. Yet even more inexplicably, several numbers have been skipped in this new series which includes only the T-1, T-3 Firefly, and T-6 Texan II. The latter case is most likely due to the legacy of the original Texan trainer of World War II fame which was also known as the T-6.

In addition, the Experimental X-plane series has never been restarted. Though the first member of this series, the X-1 predates the 1962 Tri-Service system, subsequent aircraft have continued to be numbered according to the pre-1962 values ever since.

It should also be pointed out that the suffix letters that appear at the end of aircraft designations are often not sequential. For example, certain foreign customers are typically given the same suffix letters even if that is not the next available letter. Examples include the F-4K sold to the United Kingom, the F-15J for Japan, and the F-16I sold to Israel. Many aircraft have also been given unusual suffixes such as the AV-8B+, F-14A+, and F-16CJ. These are typically for unofficial use only.

Finally, for the truly picky, here is the full text of the official Tri-Service MDS system as specified by Air Force Joint Instruction 16-401 of 1 September 1997.
- answer by Jeff Scott, 23 June 2002

I want to know what parameters indicate the generation of an aircraft, both military and civilian. For example, the F-14 is considered a fourth generation fighter. Can you sort aircraft by their generations?

In the article dealing with the aircraft numbering system in use by the military, the information about the F-18 should be changed. The original design of the aircraft was the F-17. It was changed after the McDonnell company took the original project over from Northrop.

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