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National Stock Number (NSN)
In order to manage the huge number of individual items of supply that are bought, stocked, stored, issued, and used by the U.S. military, an inventory numbering system was essential. In World War II each branch of the services had their own system, the Army and Navy as well as individual departments such as Medical Department or Quartermaster. It was common to find a different name applied to the same item. It could be hard to locate supplies and harder to share.
History of the U.S. Government National Stock Number (NSN)
Experience in World War II showed that it was unworkable for each service to have its own part numbering system. Even within one service, a variety of manufacturers’ item names for identical parts created inconsistencies in the various logistics management systems, making it difficult to control inventories. A common language of supply was needed to manage the growing complexity.
As part of the post-war reorganization that created the Department of Defense (DoD), in July of 1947, the Army-Navy Munitions Board established the Cataloging Agency to manage a single DoD resource called the Joint Army-Navy Catalog System. In 1949, the Federal Stock Number (FSN) system was established with an eleven digit number and the first FSN was assigned. On 1 July 1952, the Defense Cataloging and Standardization Act mandated a single catalog system for DoD. In 1958, the Armed Forces Supply Support Center (AFSSC) was established in Washington, DC, to maintain the Federal Catalog System and standardize item names used by the military services. When the Defense Supply Agency was created on 1 January 1962, the AFSSC was renamed the Defense Logistics Service Center, becoming the central control point for the Federal Catalog System. The Defense Logistics Service Center was later renamed the Defense Logistics Information Service (DLIS).
A major upgrade to the catalog system occurred in 1975 with the implementation of the Defense Integrated Data System. The main change was the expansion of the eleven digit FSN to the thirteen digit National Stock Number (NSN), by adding a two digit NATO country code (see below).
Assigning National Stock Numbers (NSNs)
The Defense Logistics Information Service (DLIS) at the Battle Creek Federal Center in Michigan performs NSN assignments, initiated whenever a new item is ordered repeatedly, or when a new weapons system is built and put into service. Each NSN that is assigned to an item is the result of a careful review process called cataloging. All U.S. military services, as well as NATO and allied countries, submit cataloging requests to DLIS for processing. The information is held in the Federal Logistics Information System (FLIS) managed by DLIS in Battle Creek. DLIS operates within the Defense Logistics Agency (DLA) and is the only organization that is authorized to assign NSNs.
National Stock Numbers are assigned based on the end use of the item and cover everything from large, complex items like a weapon or truck to tiny individual components. As of 2005, there were about 14 million active and inactive NSNs in the FLIS.
Some examples of actual NSNs:
Structure of the National Stock Number (NSN)
The configuration of the NSN is a 13-digit number, as the examples above show. It is composed of these overlapping sub-groups:
The first two digit positions identify the Federal Supply Group (FSG), the broad category in which the item belongs. For the HMMWV or M-151A2, the FSG is 23, defined as:
The FSG is followed by two additional positions which together with the FSG form the four position Federal Supply Class (FSC). The FSC narrows the category down to something more specific. In the case of the HMMWV or M-151A2, the FSC is 2320, defined as:
The last 9 positions (e.g. 01-371-9577) are the National Item Identification Number (NIIN) and identify the specific item. The first two positions of the NIIN identify the NATO country code for the country making the number assignment. The codes 00 and 01 are used by the United States. The last seven digits of the NIIN are the item serial number. The serial number does not follow an assignment pattern as the FSG, FSC and country code do; it is merely a number chosen for the item.
When the FSN was converted to the NSN in 1975, existing FSNs were typically changed over by simply adding "00" between the FSC and the serial number. For example, "First Aid Kit, General Purpose, Rigid Case", FSN 6545-922-1200, was changed to NSN 6545-00-922-1200.
If an item is issued in different sizes, each size will have its own NIIN. Sometimes all the sizes follow a logical pattern, sometimes not. When items from different manufacturers perform the same function, have the same characteristics, and are the same size, a single NSN may be assigned. For example, all flashlight standard Alkaline D-cell batteries have the same NSN regardless of supplier (6135-00-835-7210).
Because the FSC is assigned based on end use, it is possible for the same item to be in more than one FSC. For example, a cleaning compound could be assigned FSC 6850 when used for general purpose cleaning, but the same chemical composition would be assigned FSC 6750 when used as a photographic cleaner. In each case, the NIIN would be different.
Variations in the National Stock Number (NSN)
When an NSN is assigned to an item, that reflects the situation at a particular point in time. Later, different specifications or suppliers, usage changes, or just bureaucratic shuffling may result in a new NSN being assigned to the same or a very similar item. This can be confusing, especially if the change is merely one of nomenclature with little or no change to the physical item. It means that you have to be cautious in the use of NSNs, especially for items from the past where it may be difficult to discover all the relationships that may have been in play when the item was originally developed, tested, procured, and fed through the military logistics system. If you find an NSN referenced in print or on a web page, be aware that it may not be the only NSN that applies to the item. If the item has to fit with something else (like a set of poles for a tent) then the exact, correct NSN may depend on the NSN of the related item it has to fit with.
For example, the Improved Rain Suit went through a number of minor design changes plus color changes from olive drab to camouflage pattern resulting in a series of NSNs being assigned, as shown in a table on the linked page. If you are looking for an Improved Rain Suit in surplus channels, any of the NSNs may be used depending on the date, model, color and size details. If you are ordering one through military supply channels, then be careful to use the most current, actively supported NSN that applies to the authorized item.
Changing NSNs are announced through military publications, but its very time consuming to keep up. PS Magazine tries to help, as in the example to the right.