Miscellaneous Designation Systems

Copyright © 2000-2026 Andreas Parsch

1 Army Nomenclature System

2 Navy MARK/MOD Nomenclature System

3 Joint Photographic Type Designation System

4 Telecommunications Security (TSEC) Nomenclature System

5 Joint Optical Range Instrumentation Type Designation System

6 Sources

This article explains designation systems, which are not specific to military aviation related equipment, but which are nevertheless regularly encountered when studying the subject.

1 Army Nomenclature System

The Army designates most types of equipment in accordance with the Army Nomenclature System (formerly known as Ordnance Nomenclature System) as defined in MIL-STD-1464A. These type designators are generally known as "Ordnance Numbers" or "M"-numbers. A designation is usually assigned as soon as a new equipment item enters the Army inventory. The numerical type designators are not "globally" unique, but only within a certain category of equipment, like tanks, armoured vehicles, guns, etc. Therefore, the full designation for an item designated within this system must always include an item name.

(1) is the name of the item, which is part of the complete nomenclature. According to MIL-STD-1464A, the name must be written in capital letters, and is to be followed by a colon. The name should be selected from DoD Cataloging Handbook H6 ("Federal Item Name Directory").

Number (2) is an arbitrary number. The numbers are usually assigned in numerical sequence within each equipment category. Since the latest change of MIL-STD-1464A, dated 17 February 2023, the sequential assignment is no longer specified in the regulations. Now the number has only to be unique within the numbers of currently fielded items of each equipment category. This allows for skipping of numbers, as well as reuse of older numbers which are no longer in use.

Two different prefixes (3) are used:

• XM - Item is in the development or pre-production phase
• M - Item is classified as "standard"

(4) is an optional letter/number suffix used to denote modifications of the equipment. Two different letters are used:

• A - Alteration (modification of service equipment)
• E - Experimental

Modifications of service equipment use the suffixes A1, A2, etc., while experimental modifications use suffixes E1, E2, etc. These suffixes can be combined, e.g. M547A2E1 would be the first experimental modification of the second modification (i.e. third version) of the M547 item. If the M547A2E1 would be accepted as a standard service item, the designation would change to M547A3.

Note: According to MIL-STD-1464A, dashes or spaces must not be used in Army Nomenclature numerical designators. E.g., only M1A1 is correct nomenclature, while variants like M-1A1 or M1-A1 are incorrect.

Historical Information

The U.S. Army assigned model numbers with an M prefix to some type of equipment (e.g. rifles) almost since its inception. But the numbers in these early designations were always the year, in which the equipment was fielded. Other equipment (e.g. artillery projectiles) was designated with "Mark" (MK.) and a roman numeral. In July 1925, all these designation systems were replaced by the curent one, where M numbers are assigned sequencially form 1 up, separately for every category of equipment.

In the original form of the designation system, equipment, which was tested or evaluated, received designations with a T prefix (possibly standing for "Trial" or "Test") instead of M, followed by a consecutive number for each category. When becoming standard equipment, the T number was replaced by the next available M number in the respective equipment series. At some time in the 1950s, this system was gradually changed to the current one, where experimental or test items receive XM prefixes, with the number already in the proper M sequence. This has the advantage, that only the prefix, but not the number, changes, when the equipment is standardized.

Selected Designation Listings

Bombs
Rockets
Cartridges & Projectiles

2 Navy MARK/MOD Nomenclature System

The Navy assignes MARK/MOD numbers to nearly all types of equipment not covered by other designation systems, e.g. torpedoes, mines, guns, missile launchers, etc. This MARK/MOD system has its origins in the early 20th century, and was formally adopted in 1944. Of course, it was revised and extended over time, and the current standard is defined in MIL-STD-1661.

Similar in concept to the Army Nomenclature System, the full nomenclature for an equipment item consists of a type name and the MARK/MOD numbers. Examples are:

(1) is the name of the item, which is part of the complete nomenclature. According to MIL-STD-1661, the name is to precede the MARK number, and separated from the latter by a comma. The name should be selected from DoD Cataloging Handbook H6 ("Federal Item Name Directory"). In tabulated equipment listings, the item names should be written in "inverted nomenclature", in which the usual order of words in the name is reversed (as in the list of examples). That way, related items will be grouped together in alphabetical listings.

Number (2) is the MARK number. MARK numbers are assigned in numerical sequence within each equipment category. The prefix EX instead of MARK is used for experimental or developmental items. If an EX item is adopted for operational use, it will use MARK afterwards, but will keep the assigned number.

Number (3) is the MOD number, which indicates a modification or variant of the equipment. MOD numbers are assigned in numerical sequence for each equipment, the initial version being designated MOD 0. When an item is redesignated from EX to MARK, the MOD numbers for "MARK" are restarted from Zero. An example will clarify this: An experimental item is designated EX 44, and the MOD numbers 0 through 5 were assigned during development. Now it is decided to put MOD 1 and MOD 5 into operational service. Then EX 44 MOD 1 would be redesignated MARK 44 MOD 0, and EX 44 MOD 5 would become MARK 44 MOD 1. However, if all (or nearly all) MODs of the EX series are to become operational, the MOD numbers can be retained for the MARK series, the (few) unused numbers being left unassinged in the MARK series.

The general guideline is to write the words MARK and MOD unabbreviated and in uppercase. However, abbreviation of MARK as MK and/or use of mixed-case (Mark/Mod) lettering is explicitly allowed. Dashes and other punctuations should not be used. Therefore, all the following variants are correct nomenclature:

The following variants do not conform to the strict rules of MIL-STD-1661, but are nevertheless quite common:

Selected Designation Listings

Bombs
Rockets
Cluster Bombs
Torpedoes

3 Joint Photographic Type Designation System

The Joint Photographic Type Designation System was originally defined in MIL-STD-155, and has been absorbed into the current MIL-STD-1812 on 28 February 1991. Designations are assigned to conventional film type photographic equipment. Excluded is electro-optical and other imaging equipment designated in the Joint Electronics Type Designation System.

Letter (1) designates the equipment category:

• A - Picture Using Equipment
• B - Accessories, Attachments and Components for Picture Using Equipment
• E - Picture Processing Equipment
• F - Accessories, Attachments and Components for Picture Processing Equipment
• K - Camera
• L - Accessories, Attachments and Components for Cameras

Letter (2) designates the purpose of the equipment:

• A - Reconnaissance (for categories "K" and "L" only)
• B - Strike Recording (for categories "K" and "L" only)
• C - Aerial Mapping (for categories "K" and "L" only)
• D - Scope Recording (for categories "K" and "L" only)
• E - Still Picture (not otherwise classified) (for categories "K" and "L" only)
• F - Motion Picture (not otherwise classified) (for categories "K" and "L" only)
• G - General Purpose (for categories "K" and "L" only)
• H - Processing Machine (for categories "E" and "F" only)
• J - Developer (for categories "E" and "F" only)
• K - Washer (for categories "E" and "F" only)
• L - Dryer (for categories "E" and "F" only)
• M - Miscellaneous (for categories "B", "F" and "L" only)
• N - Printer (for categories "E" and "F" only)
• P - Projector (Still Picture) (for categories "A" and "B" only)
• Q - Projector (Motion Picture) (for categories "A" and "B" only)
• R - Viewing Device (for categories "A" and "B" only)
• S - Set or System

(3) is the model number. Each two-letter Category-Purpose combination uses its own model number sequence, starting at 1. Two blocks of high model numbers (500-599, 2500-2599) are reserved for use by Canada. Most likely the first number of the Canadian block (500) is never used, i.e. Canadian designations probably always start with 501.

Letter (4) designates a modification of the equipment. The first production model will receive letter "A", the second "B", etc. Letters "I" and "O" are not used.

(5) is an optional suffix number for minor modifications.

Designation Listings

For equipment designators shown in light gray without a link, I haven't found any designations so far.

Picture Using Equipment

Picture Processing Equipment

Cameras

4 Telecommunications Security (TSEC) Nomenclature System

Most cryptographic and COMSEC equipment used by the US military and civilian intelligence agencies is designated in the Telecommunications Security (TSEC) nomenclature. This nomenclature system was introduced by the NSA in the 1950s in Regulation 90-2 "Nomenclature for Communication Security Materials". It has been updated and extended over the decades, and the current standard is defined by the Committee on National Security Systems (CNSS) in their document CNSSI No. 4403.

The nomenclature for equipment systems, equipment and assemblies (i.e. components) is slightly different.

Designators for equipment and systems are always prefixed by "TSEC/", while designations for assemblies use a "/TSEC" suffix. However, assembly designations are sometimes incorrectly quoted with a "TSEC/" prefix.

Letter (1) is the function of the equipment:

• C - COMSEC Equipment System
• G - General Purpose
• K - Cryptographic
• H - Crypto-Ancillary
• M - Manufacturing
• N - Noncryptographic
• S - Special Purpose

Letter (2) is the purpose of the equipment:

• G - Key Generation
• I - Data Transmission
• L - Literal Conversion
• N - Signal Conversion
• O - Multipurpose
• P - Materials Production
• S - Special Purpose
• T - Testing, Checking
• U - Television
• W - Teletypewriter
• X - Facsimile
• Y - Speech

Letter (3) is only used for designations of assemblies and designates the type of the assembly:

• A - Advancing
• B - Base or Cabinet
• C - Combining
• D - Drawer or Panel
• E - Strip or Chassis
• F - Frame or Rack
• G - Key Generator
• H - Keyboard
• I - Translator or Reader
• J - Speech Processing
• K - Keying, Permuting
• L - Repeater
• M - Memory or Storage
• O - Observation
• P - Power Supply or Converter
• R - Receiver
• S - Synchronizing
• T - Transmitter
• U - Printer
• V - Removable Communication Security Component
• W - Logic Programmer/Programming
• X - Special Purpose

(4) is the item number. Originally, item numbers for equipment and systems were assigned sequentially starting from 1, with separate series for each 2-letter prefix. The sequential numbering has been dropped, and nowadays the numbers only have to be unique. For assemblies which are used only as part of a specific equipment, the item number is identical to the number of the equipment. If an assembly is used with multiple types of equipment, its item number is an arbitrary unique number.

The optional suffix letter (5) denotes a specific version of the equipment or assembly. The first version uses no suffix, the first modifcation uses "A", etc.

(6) is an optional suffix number, which can be used to identify variations of a COMSEC equipment system.

An optional model designator (7) can be appended to the item nomenclature during the development and preproduction phase of an item. It consists of a letter and a number in parentheses. The following letters are defined:

• X - Exploratory Development
• V - Advanced Development
• E - Engineering Development
• P - Preproduction

The number is a sequential number for each development phase. E.g. (V2) would identify the second model in the advanced development phase.

Originally, the separator (8) between the letter prefix and the item number was a dash. The latest standard explicitly requires a space character as separator, giving "TSEC/KG 43A" as an example. This also applies to the system variation suffix (6). However, most public references, including official documents, still use a dash.

5 Joint Optical Range Instrumentation Type Designation System

This is a very obscure and long obsolete designation system. It is probably completely irrelevant to military aviation and I don't know any actual designations, but it's included for completeness.

The system was introduced on 4 December 1964 in MIL-STD-787. Obviously, someone thought that optical range instrumentation equipment should receive rationalized designations (the early 60's were high time for joint designation systems!). MIL-STD-787 was finally cancelled on 05 December 1995 - maybe because nobody really used the system?

The designation system followed the general lines of the Joint Electronics Type Designation System and distinguished between end items and components.
End Items were designated as follows:

All designations were prefixed by "ORI/", which stood for "Optical Range Instrumentation".

Letter (1) indicated the type of of the equipment:

• A - Mount
• B - Camera
• C - Cinetheodolite
• D - Tracking Telescope
• E - Electro-Optical Device
• F - Boresight
• G - Shelter
• H - Ballistic Camera
• J - TV Type Equipment
• K - Radiometric Equipment
• L - Spectrographic Equipment
• M - Laser Equipment
• N - Infrared Equipment
• P - Test and Calibration Equipment
• Q - Multipurpose Equipment
• R - Photo Theodolite
• Y - Other

Letter (2) indicated the characteristics of the equipment:

• A - Non-Tracking
• B - Manual Tracking
• C - Power Tracking
• D - Automatic Tracking
• E - Remote Controlled
• F - Single Exposure
• G - Pulse Operated
• H - Cine, high speed (over 500)
• J - Cine, low speed (to 500)
• K - Rotating Prism
• L - Streak
• M - Slit
• N - Ribbon Frame
• P - Visual
• Q - Sky Screen Tracking
• Y - Other

Letter (3) indicated the installation location of the equipment:

• A - Fixed
• B - Mobile
• C - Portable
• D - Transportable
• E - Laboratory
• F - Aircraft
• G - Underwater
• H - Shipboard
• J - Aerial Platform
• K - Special or Combination
• L - Space Platform
• M - Other
• Y - Other

(4) is the model number. Each Type-Characteristics-Installation letter combination used its own model number sequence, starting at 1.

The optional suffix letter (5) denoted a specific version of the equipment. The first version used no suffix, the first modifcation used "A", etc.

Parts and components of equipment items were designated as follows:

The two-letter code (1) indicated the type of component:

• BS - Boresight Scope
• CH - Chassis (Vehicle)
• CU - Control Unit
• DR - Digital Readout
• DS - Drive Section
• DT - Optical Data Train
• EX - Exposure Control
• FC - Film Cassette or Magazine
• OL - Objective Lens
• OS - Optical Section
• PS - Power Supply
• SS - Support Section
• SV - Servo Section
• TD - Tracking Offset Detector
• TT - Tracker's Telescope

(2) is the model number. Each type indicator used its own model number sequence, starting at 1.

The optional suffix letter (3) denoted a specific version of the equipment. The first version used no suffix, the first modifcation used "A", etc.

(4) The full type designation of a component included a slant bar, followed by the designation of the item, of which it is a part. If the component can be used with several systems, a more general designator is appended. E.g. the TT-1A/CDC is a tracker's telescope, which is used with several ORI/CBC-n items.

6 Sources

[1] MIL-STD-1464A "Army Nomenclature System", 15 February 2023
[2] MIL-STD-1661 "Mark and Mod Nomenclature System", 1 August 1978
[3] MIL-STD-155A "Joint Photographic Type Designation System", 5 August 1955
[4] MIL-STD-1812A "Aeronautical and Support Equipment Type Designation System", 9 October 2020
[5] NSA Regulation 90-2 "Nomenclature for Communication Security Materials"
[6] Committee on National Security Systems: CNSSI No. 4033 "Nomenclature for Communication Security Material", 14 November 2012
[7] MIL-STD-787 "Joint Optical Range Instrumentation Type Designation System", 4 December 1964

(The designation listings were compiled using a wide variety of sources, not the least of which were the Internet and contributions by fellow researchers.)

Back to U.S. Military Aviation Designation Systems

---

Last Updated: 1 November 2026