Aircraft Designations, United States

The United States Army Air Force (USAAF) followed a 1924 system which included function and model number as the basic elements of an aircraft\'s designation. This system, however, was very different from that used by the US Navy (USN) which is explained separately below. This dual designation system was not unified until 1962 when a common system was finally adopted by all four branches of the military. It is also worth mentioning that in 1948, shortly after World War II, the USAF changed its designation system once again. The USAAF system was based on six elements though only the first four are commonly used. The basic designation included function and a model number after a hyphen. Model numbers were assigned sequentially depending on function. Thus, the P-51 was the fifty-first pursuit (fighter) aircraft designed for the USAAF. Model numbers were, for the most part, never repeated even if a design was canceled or unsuccessful while the "unlucky" number 13 was often skipped.

Variants were designated with a series letter suffix after the model number. Using the Mustang example, the P-51A was the initial production variant. Series letters was almost always sequential although some interesting cases involved different series for the same aircraft built in different factories, like was the case with the P-51B (built at North American\'s Inglewood factory) and the identical P-51C (built in their Dallas factory). For some strange reason, some aircraft with structural changes did not incur in a series change, this was the case with the P-47D which was produced in in both razorback and bubble-canopy versions. Though not generally seen in most public specifications, USAAF aircraft also featured a block number after the series. These reflected different production runs, which sometimes featured very minor variant changes. After the block number was the manufacturer identification which designated the factory where the production run was undertaken. Thus, the complete designation of a certain production run of the Mustang could be the P-51B-10-NA, where the 10 reflected the production block, and NA designating the North American Inglewood factory. For simplicity reasons, block numbers and manufacturer ids are not included in this site unless there\'s a significant difference between them.

Finally some variants featured a status prefix before the function. These usually indicated prototype or pre-production variants. For example, the XP-51D was the prototype version of the P-51D production variant of the Mustang. Status prefixes are explained in detail in the chart below. After 1941, the USAAF began assigning official names to aircraft. The naming system was for the most part arbitrary with some manufactures using similar names for similar aircraft. The best example for the USAAF is the Boeing series of heavy bombers which were known as "Fortresses", like the Boeing B-17 Flying Fortress and its successor the B-29 Superfortress.

The US Navy (USN) had a very different system from the USAAF. This system had been used since 1922 and was eventually copied by the Japanese Navy. The basic designation system of the USN included the aircraft function, model and manufacturer. The function letter came first, a complete list of functions can be seen in the chart below. This was followed by a sequential number related to the manufacturer (unlike the Japanese system which was related to the function). Finally, a letter suffix indicated the manufacturer. To better illustrate this, the F4U Corsair was the fourth fighter built by Chance-Vought (manufacturer code U) for the USN. It is worth mentioning that the first model of a same function built by a certain manufacturer did not have a model number. Thus, the first fighter designed by Chance-Vought was known simply the FU, not as the F1U. Confusion begins to arise since manufacturer letters were frequently used by more than one company and model numbers were not allowed to repeat among the same letter. Thus, the F2A Buffalo was actually not the second fighter built by Brewster since an earlier FA design had been originally drawn up by General Aviation which had also been assigned the manufacturer letter A before Brewster.

Variants were designated by a dash followed by a sequential variant number known as the Aircraft Configuration Sequence. Should more differentiation be necessary, a sub-variant letter was appended at the end, this was known as the Special Purpose Suffix. This means that the F4U-1A is the first variant of the Corsair which additionally featured a raised cabin and improved cockpit glazing. The Special Purpose Suffix caused further confusion as it was not sequential and the same letter frequently referred to different things. Like the USAAF, an experimental prefix was used to designate prototypes, thus, the XF4U-1 was the first prototype of the Corsair.

Perhaps the most confusing part of the USN designation system was that the manufacturer code was applied based on the company which built that particular variant of an aircraft, not necessarily the company which designed it. A good example of this is the TBF Avenger torpedo-bomber, designed by Grumman (manufacturer code F). We have the initial production variant of the Avenger known as the TBF-1 (built by Grumman) while a follow-up variant known as the TBM-3 built by General Motors. At first glance these appear to be different aircraft but in fact are simply different versions of the same basic design built in separate plants.

Unlike the Japanese system where aircraft were always designated depending on the service that assigned the aircraft requirement, the USN and USAAF used different designations for those aircraft which both services used. The best example of this is the B-24 Liberator bomber which in USN service was known as the PB4Y reflecting its new role as a maritime patrol bomber. Likewise the SBD Dauntless dive bomber in USAAF service was known as the A-24. Finally, the USN (like the USAAF) eventually adopted an official naming system beginning in 1941. Names were arbitrary but we could see certain companies assigning similar names to their aircraft. The most notable case in the USN is Grumman, who\'s fighters were given "cat" names like the F4F Wildcat and F6F Hellcat. This particular tradition has continued to this day.

To avoid the confusion of using separate designation systems for the different services (often for the same aircraft), a uniform system was established in 1962 for the US Armed Forces and which has been in use since then. It is generally quite similar to the revised USAF system used after 1948 which was notable for introducing the F designation for fighters rather than the archaic P thus transforming some legendary aircraft still in use like the P-51 into the F-51. The US Navy was particularly affected as all its then-current aircraft were radically changed such as the McDonnell F4H becoming the F-4. For those aircraft which were relatively new in 1962, the new designations quickly replaced their old ones although older Korean War-era planes up to this day remain better known by their previous nomenclature.

The new system is characterized by a four-letter designation indicating the aircraft\'s role, followed by a hyphen, a model number, and a letter suffix for variants. The first letter to the left of the hyphen indicated the vehicle type but this was not present in normal aircraft, only on other craft such as helicopters, gliders and VTOL planes. The second letter to the left, and the most important since it was the first letter of normal aircraft, referred to its basic mission. Thus, the A-10 is a normal attack aircraft whereas the AV-8 is a VTOL attack aircraft and the AH-64 an attack helicopter. The third letter to the left was optional and described the modified mission if present (in other words, a variant of an aircraft which performed a different role) such as the RAH-66 attack helicopter with reconnaissance capability or the KC-130 tanker variant of the Hercules transport. Finally, a status prefix was added in case the aircraft was not standard as is case of experimental models and prototypes such as the YF-22 prototype Raptor fighter. On occassion there are exceptions to these rules, most notably the FB-111 which was a bomber variant of the F-111 whose correct designation should have been BF-111 and also the F-117, commonly known as the "Stealth Fighter", but which is in fact an attack aircraft with no air-combat capability whatsoever. Also, the unconventional F/A-18 designation of the Hornet refers to the fact that there had originally been two versions (a fighter and an attacker) but were later merged into one.

To the right of the hyphen is the design number which is generally sequential followed by a letter suffix indicating the series, or variant (also supposedly sequential). Finally, block numbers and manufacturer codes (each preceded by a hyphen) are also part of the designation system although seldom used ordinarily. A full example would be the F-4G-43-MC which refers to Block 43 of the G variant of the fourth fighter designed by McDonnell. The new 1962 designation system also called for design numbers to be reset back to 1, most likely since various aircraft types (fighters and transports) had surpassed the century mark. Nevertheless there are also a number of glaring exceptions to the numeration rules regarding aircraft which are out of sequence. Again, the F-117 comes to mind especially considering that it was originally believed to be designated the F-19, a number which was mysteriously skipped. More recently, the successor to the B-2 bomber has been announced as the B-21, the number making reference to the 21st century. However, the aircraft is still in development which means that its official designation once in service could end up being sequential.

Like before, post-1962 names are generally arbitrary although companies occasionally recycle previous successful names on their newer aircraft. During the Cold War, many companies also followed similar naming patterns such as McDonnell (supernatural names), Vought (pirate names), Douglas ("Sky" prefix), and Republic ("Thunder" prefix) although this practice has become far less prevalent given the reduced number of designs and manufacturers in the industry today. Non-naval helicopters are also usually given the name of Native American tribes.