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.
Examples:GUIDED MISSILE, SURFACE-TO-AIR:XM3E1MAIN BATTLE TANK:M1A1CANNON, 20MM:XM301PROJECTILE, 155MM:M547A2E1(1)(3)(2)(4)
(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 assigned in numerical sequence within each equipment category.
Two different prefixes (3) are used:
XM - Item is in the development or pre-production phaseM - 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.