1962 United States Tri-Service aircraft designation system
The Tri-Service aircraft designation system is a unified system introduced in 1962 by the United States Department of Defense for designating all U.S. military aircraft. Prior to then, the U.S. armed services used separate nomenclature systems. Under the tri-service designation system, officially introduced on 18 September 1962, almost all aircraft receive a unified designation, whether they are operated by the United States Air Force (USAF), United States Navy (USN), United States Marine Corps (USMC), United States Army, or United States Coast Guard (USCG). Experimental aircraft operated by manufacturers or by  NASA are also often assigned designations from the X-series of the tri-service system. The 1962 system was based on the one used by the USAF between 1948 and 1962, which was in turn based on the Type, Model, Series USAAS/USAAC/USAAF system used from 1924 to 1948. The 1962 system has been modified and updated since introduction. History. The Tri-Service system was first enacted on 6 July 1962 by the DoD Directive 4505.6 "Designating, Redesignating, and Naming Military Aircraft" and was implemented via Air Force Regulation (AFR) 66-11, Army Regulation (AR) 700-26, Bureuea of  Weapons Instruction (BUWEPSINST) 13100.7 on 18 September 1962. Anecdotally, the Tri-Service system was partly brought about due to Secretary of Defense Robert McNamara's confusion and frustration with the different designation systems the Navy and Air Force used at the time which resulted in the F-4H and F-110 both being used to refer to, essentially, the same aircraft. The 1962 Tri-Service system was modified in 1971 by the Joint Regulation 4120.15E. Designation system. The designation system produces a "Mission-Design-Series" (MDS) designation of the form: Of these components, only the "Basic Mission", "Design Number" and "Series Letter  are mandatory. In the case of special vehicles a Vehicle Type" symbol must also be included. The U.S. Air Force characterizes this designation system as "MDS", while the Navy, and Marine Corps refer to it as "Type/Model/Series" (T/M/S). Status prefix. These optional prefixes are attached to aircraft not conducting normal operations, such as research, testing and development. The prefixes are: A temporary special test means the aircraft is intended to return to normal service after the tests are completed, while permanent special test aircraft are not. The Planning code is no longer used but was meant  to designate aircraft "on the drawing board". For example, using this system an airframe such as the F-13 could have initially been designated as ZF-13 during the design phase, possibly XF-13 if experimental testing was required before building a prototype, the YF-13; the final production model would simply be designated F-13 (with the first production variant being the F-13A). Continuing the example, some F-13s during their service life may have been used for testing modifications or researching new designs and designated JF-13 or NF-13; finally after many years of service, the airframe would be permanently grounded due to safety or  economic reasons as GF-13. Modified mission. Aircraft which are modified after manufacture or even built for a different mission to the standard airframe of a particular design are assigned a modified mission code. They are: The multi-mission and utility missions could be considered the same thing; however they are applied to multipurpose aircraft conducting certain categories of mission. M-aircraft conduct combat or special operations while U-aircraft conduct combat support missions, such as transport (e.g., UH-60) and electronic warfare (e.g., MC-12). Historically, the vast majority of U.S. Coast Guard air assets included the H-code (e.g., HH-60 Jayhawk  or HC-130 Hercules). In the 21st century, the Coast Guard has used the multi-mission designation for their armed rescue helicopters (MH-60 Jayhawk or MH-65 Dolphin). Basic mission. All aircraft are to be assigned a basic mission code. In some cases, the basic mission code is replaced by one of the modified mission codes when it is more suitable (e.g., M in MH-53J Pave Low III). The defined codes are: The rise of the multirole fighter in the decades since the system was introduced has created some confusion about the difference between attack and fighter aircraft. According to the current  designation system, an attack aircraft ("A") is designed primarily for air-to-surface missions (also known as "attack missions"), while a fighter category "F" incorporates not only aircraft designed primarily for air-to-air warfare, but also multipurpose aircraft designed also for attack missions. The Air Force has even assigned the "F" designation to attack-only aircraft, such as the F-111 Aardvark and F-117 Nighthawk. The only "A" designated aircraft currently in the U.S. Air Force is the A-10 Thunderbolt II. The last front line "A" designated in the U.S. Navy and Marine Corps was the A-6 Intruder, with the  only strictly "A" designated fixed-wing aircraft remaining is the A-29 Super Tucano leased under the "Imminent Fury" program. Of these code series, no normal aircraft have been assigned a "K" or "R" basic mission code in a manner conforming to the system. Vehicle type. The vehicle type element is used to designate the type of aerospace craft. Aircraft not in one of the following categories (most fixed-wing aircraft) are not required to carry a type designator. The type categories are: A UAV control segment is not an aircraft, it is the ground control equipment used to command a  UAV. Only in recent years has an aircraft been designated as a spaceplane, the proposed MS-1A. Design number. According to the designation system, aircraft of a particular vehicle type or basic mission (for manned, fixed-wing, powered aircraft) were to be numbered consecutively. Numbers were not to be assigned to avoid confusion with other letter sequences or to conform with manufacturers' model numbers. Recently this rule has been ignored, and aircraft have received a design number equal to the model number (e.g., KC-767A) or have kept the design number when they are transferred from one series to another (e.g., the  X-35 became the F-35). Series letter. Different versions of the same basic aircraft type are to be delineated using a single letter suffix beginning with "A" and increasing sequentially (skipping "I" and "O" to avoid confusion with the numbers "1" and "0"). It is not clear how much modification is required to merit a new series letter, e.g., the F-16C production run has varied extensively over time. The modification of an aircraft to carry out a new mission does not necessarily require a new suffix (e.g., F-111Cs modified for reconnaissance are designated RF-111C), but often a new letter is assigned  (e.g., the UH-60As modified for Search and Rescue missions are designated HH-60G). Non-systematic aircraft designations. Since the 1962 system was introduced there have been several instances of non-systematic aircraft designations and skipping of design numbers. Non-systematic or aberrant designations. The most common changes are to use a number from another series, or some other choice, rather than the next available number (117, 767, 71). Another is to change the order of the letters or use new acronym based letters (e.g. SR) rather than existing ones. Non-systematic designations are both official and correct, since the DOD  has final authority to approve such designations. Skipped design numbers. The design number "13" has been skipped in many mission and vehicle series for its association with superstition. Some numbers were skipped when a number was requested and/or assigned to a project but the aircraft was never built. The following table lists design numbers in the 1962 system which have been skipped. Manufacturer's code. From 1939, a 2-letter manufacturer's code was added to designations to easily identify the manufacturer and the production plant. For example, F-15E-50-MC, the "MC" being the code for the McDonnell Douglas plant  at St. Louis, Missouri. Block number. In 1941 block numbers were added to designations to show minor equipment variations between production blocks. The block number appears in the designation between the model suffix and manufacturers code (for example F-100D-85-NH). Initially they incremented in numerical order -1, -2, -3 but this was changed to -1, -5, -10, -15 in increments of five. The gaps in the block numbers could be used for post-delivery modifications, for example a F-100D-85-NH could be modified in the field to F-100D-86-NH. Not all types have used block numbers. 1962 United States Tri