F-16 Reference

US Tri-Service Designation System Electronic Equipment

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In 1962, the US Military adopted the so-called "Tri-Service" designation system, which is still used today. Under the system, the three services (USAF, USN and USMC) were to use common designations for aircraft, guided missiles and electronic equipment. The conventions are described in the DEPARTMENT OF DEFENSE PUBLICATION 4120.15-L and are officially known as the MDS (MISSION, DESIGN, AND SERIES SYSTEM). Below are the details of the designation system for electronic equipment:

General Format

A typical designation for electronic equipment has the following format:

with X for an arbitrary letter and the hash-mark for an arbitrary digit. Not all letters or digits are necessarily used, and AN/ is optional. All characters have a special signification, according to their position in the designation:

  1. Joint Service Indicator
  2. AN is the optional joint service indicator, seperated from the rest of the designation by a slash. The numbers of the sections below correspond with the numbers in the figure above.

  3. Platform / Installation
  4. Indicates the nature of the platform on which the equipment is installed.

    Platform / Installation
    Prefix Platform
    AAirborne (Piloted Aircraft)
    BUnderwater Mobile (Submarine)
    CAir Transportable
    DPilotless Carrier
    FFixed (Ground)
    GGeneral Purpose Use
    MGround Mobile
    TGround Transportable
    UGeneral Utility Assemblies
    VGround Vehicular
    WWater Surface and Underwater Combination
    ZPiloted and pilotless airborne combination

  5. Equipment Type
  6. Indicates the type or nature of the equipment.

    Equipment Type
    Prefix Type
    AInfrared or Invisible Light
    CCarrier (Wire)
    GTelegraph or Teletype
    IInterphone or Public Address
    JElectromechanical or Inertial Wire Covered
    NSound in Air
    QSonar and Underwater Sound
    SSpecial Types, Magnetic Combination of Types
    VVisual or Visible Light
    XFacsimile or TV
    YData Processing

  7. Purpose
  8. Indicates the primary task for which the equipment was designed.

    Prefix Purpose
    AAuxilary Assemblies
    DDirection Finding, Recon, and/or Surveillance
    EEjection and/or Release
    GFire Control or Light Finding
    HRecording / Reprocucing
    MMaintenance or test assemblies
    NNavigational Aids
    QSpecial or Combinations of Purposes
    RReceiving / Passive Detection
    SDetecting and/or Range Bearing, Search
    WAutomatic Flight / Remote Control
    XIdentification and Recognition
    YSurveillance and Control

  9. Design Number
  10. Supposedly in sequential order, it indicates the model of the vehicle within the basic mission category

  11. Series
  12. Indicates (alphabetically) major modifications to the original design, which is indicated by the A. I and O are usually skipped in order to avoid confusion with the 1 and the 0.

  13. Configuration Number
  14. Indicates a minor modification.


The AN/ALQ-131B is a Joint-Service, airborne countermeasures device for special purposes, model nr.131, modification B.

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