US Military Aircraft Designation Systems

Prior to 1962, the US Air Force and US Navy each had their own designation systems for their aircraft. The following information on the early Air Force and Navy designations is borrowed from the rec.aviation.military FAQ:
  1. USAAF (US Army Air Force) system, adopted 1924

    A designation consists of a letter (or set of letters) indicating the type and mission of the aircraft, and a sequence number indicating a specific aircraft within a category, separated by a hyphen. The number may be followed by a series letter to indicate a variant of an aircraft. Most aircraft are also given a proper name, but this is not part of the formal designation.

    Mission codes used in the USAAF system included the following:

        A  = Attack
        AG = Assault glider
        AT = Advanced trainer
        B  = Bomber
        BC = Basic combat
        BG = Bomb glider
        BQ = Guided bomb
        BT = Basic trainer
        C  = Cargo transport
        CG = Cargo glider
        CQ = Target control
        F  = Photographic reconnaissance
        FG = Fuel-carrying glider
        FM = Multiplace fighter
        G  = Gyroplane
        GB = Glide bomb
        GT = Glide torpedo
        JB = Jet-propelled bomb
        L  = Liaison
        O  = Observation
        OA = Observation amphibian
        OQ = Target
        P  = Pursuit
        PB = Biplace pursuit
        PG = Powered glider
        PQ = Manned target
        PT = Primary trainer
        R  = Rotorcraft
        TG = Training glider
    These codes were sometimes modified by one of the following prefixes, indicating a special status or modification:
        C = Cargo transport
        F = Photographic reconnaissance
        K = Ferret
        R = Restricted operations
        T = Trainer
        U = Utility
        V = Staff/VIP transport
        X = Experimental
        Y = Service test
        Z = Obsolete
    The first version of a type had no series letter; the second was suffixed with "A", the third with "B", and so on. To avoid confusion with the numbers "1" and "0", the letters "I" and "O" were usually skipped. For example, the B-29A is the second version of the 29th bomber aircraft identified by the USAAF.
  2. USAF (US Air Force) system, adopted 1948

    The USAF system (1948) was similar to the USAAF system; it retained the three-part code, although the series letters now started with "A" for the first version rather than the second. The mission codes were rationalized somewhat. For example, "F" for "Fighter" replaced "P" for "Pursuit" (the existing P-series aircraft were redesignated, and new aircraft receiving F-series numbers continuing the old P-series). Similarly, "H" for "Helicopter" replaced "R" for "Rotorcraft", and "R" for "Reconnaissance" replaced "F" for "Photographic". The "L" for "Liaison" code was replaced by "O" for "Observation", and most of the two-letter codes were combined into one (e.g. a single "T" series replaced the old "AT", "BT", and "PT").

  3. USN (US Navy) system

    Before the adoption of the Tri-Service system in 1962, the US Navy had its own system of aircraft designations, completely different from that used by the USAAF and USAF. This system consisted of up to five parts:

    (1) One or two letters to indicate the function. These included:

        A  = Attack
        BF = Fighter-bomber
        F  = Fighter
        HC = Transport helicopter
        HO = Observation helicopter
        HU = Utility helicopter
        J  = Utility
        N  = Trainer
        O  = Observation
        P  = Patrol
        PB = Patrol bomber
        R  = Transport
        SB = Scout bomber
        T  = Trainer
        TB = Torpedo bomber
        W  = Early warning
    (2) A sequence number, to distinguish between aircraft of the same function built by the same manufacturer. The number was left out if it was 1.

    (3) A letter to indicate the manufacturer. Because the US Navy used aircraft from considerably more than 26 different manufacturers, most of the letters of the alphabet were shared between several companies. The same company also frequently used more than one letter at various times. If the same aircraft was built by more than one firm, the designation was changed to reflect the individual manufacturers. For example, the Chance-Vought F4U Corsair was also built by Goodyear, whose Corsairs were designated FG. Some of the most important manufacturers were:

        A = Brewster, Noorduyn
        B = Beech, Boeing, Vertol
        C = Cessna, Curtiss, de Havilland Canada
        D = Douglas, McDonnell
        E = Cessna, Piper
        F = Fairchild, Grumman
        G = Goodyear
        H = McDonnell
        J = North American
        K = Fairchild, Kaman
        L = Bell
        M = Bell, Martin, General Motors
        O = Lockheed, Piper
        P = Piasecki
        Q = Fairchild
        S = Sikorsky, Stearman
        T = Northrop
        U = Chance-Vought
        V = Lockheed, Vultee
        W = Wright
        Y = Consolidated, Convair
    (4) After a dash, a number to indicate a subtype.

    (5) Optionally, a letter to indicate a minor variation on a subtype.

    For example, the F4U was the fourth fighter designed by Chance-Vought for the US Navy. The F4U-1A was a modified version of the first subtype of the F4U.

When Robert McNamara became Secretary of Defense under Pres. Kennedy, he found the differences between these systems so confusing that he ordered the Air Force, Navy, and Army to devise a simpler naming convention common to all three services. Thus was born the Tri-Service system of 1962. For the most part, this system is the same as the Air Force convention.

As indicated above, the numbering of aircraft was restarted at 1 when the services switched to the new system. While Air Force aircraft in service at the time retained their original designations (e.g. the F-111 and B-52), all Navy aircraft then in service were renumbered to conform to the new system:

Although the new system is much simpler and easier to understand, it hasn't always been applied faithfully. For example, why was the F-117 stealth fighter numbered under the older convention even though it was developed almost 20 years after switching to the new system? Why does it have an "F" designation when it isn't really a fighter? Why were the F-13 and F-19 designations skipped? Regardless, I hope this discussion alleviates your confusion about the diferent designation schemes used by the US military.
- answer by Jeff Scott, 4 February 2001

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