1962 United States Tri-Service aircraft designation system

Experimental aircraft operated by manufacturers or by NASA are also often assigned designations from the X-series of the tri-service system.

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, Bureau of Weapons Instruction (BUWEPSINST) 13100.7 on 18 September 1962.

[2] 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 F4H and F-110 both being used to refer to, essentially, the same aircraft.

[5][6][7] The most recent changes were mandated by Joint Regulation 4120.15E Designating and Naming Military Aerospace Vehicles[8][Note 2] and were implemented[9][Note 3] via Air Force Instruction (AFI) 16-401, Army Regulation (AR) 70-50, Naval Air Systems Command Instruction (NAVAIRINST) 13100.16 on 3 November 2020.

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).

[11] These optional prefixes are attached to aircraft not conducting normal operations, such as research, testing and development.

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).

The Air Force has even assigned the F designation to attack-only aircraft, such as the F-111 Aardvark and F-117 Nighthawk.

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.

A pair of armed Phantom jet fighters in flight at high altitude
Before the introduction of the tri-service designation system, the F-4 Phantom II was designated F4H by the U.S. Navy, and F-110 Spectre by the U.S. Air Force.