IUID Data Matrix
IUID Data Matrix

Unique Identification (UID) refers to methods and systems for creating globally unique identifiers for critical components. This idea gained traction within the aerospace and automotive industries as a way to ensure that components from different manufacturers and countries could be uniquely identified. Adding a part number to a serial number makes the combined identifier more unique. Further adding the manufacturer’s identifier and the country of origin makes it even more so. 

The use of UID was adopted by the Defense Department (DoD) to improvement identification of items across its many suppliers, and to a greater extent within the NATO environment.  The term Item Unique Identification (IUID) evolved as a way of putting a specific focus on items versus other things uniquely identified, such as people.  While use of IUID is proper and precise, few in in the defense supply chain space will be confused by the use of the UID acronym in its place.  

Most people may be unknowingly familiar with UIDs in the form of the Vehicle Identification Number, or VIN, attached to every car. Each manufacturer assigns serial numbers to the automobiles they manufacturer. But without a system to control these numbers there would be a lot of duplications, especially since everyone starts with one and counts from there.

The International Organization for Standardization (ISO) stepped in with a standard defining the VIN, which adds an ISO-assigned World Manufacturer ID and other attributes to the serial number to ensure that each is truly unique. That’s why VINs are so long.

By 2004, the US Department of Defense (DOD) had adopted the system of Item Unique Identification (IUID) that was popular with the aerospace industries of NATO countries to achieve the same result for items other than vehicles. Adding the manufacturers identifier (CAGE code or DUNS number) and item part number to serial numbers helps the DOD ensure that items are uniquely identified. The result is a Unique Item Identifier (UII), which is permanently marked on each serial managed part purchased by the DOD and placed in a huge database called the UID Registry (or more properly, the IUID Registry).

Defense contractors must submit the UII of each item it is shipping to the Government’s Wide Area Workflow (WAWF) system prior to shipping, which in turn checks these UIIs in the IUID Registry. Items found already to exist in the Registry are not accepted by the Government, thus helping to ensure that items are, in fact, uniquely identified.


  • IUID – Item Unique Identification is the DoD system put in place for improved trace ability of property, including the policies and practices to implement unique identification of items and the systems to support that.
  • UID – Unique Identification is a generic term that is often used in reference to IUID. It was often used in official publications at the early stages of IUID, leading to confusion that lessens as more precise terms are used. It is often used in reference to the physical part mark or UII, which is not wrong, just imprecise.
  • UII – The Unique Item Identifier, often referred to as “the UID”, is the string of up to 50 characters that go beyond a simple serial number to uniquely identify an item, based on global standards and recognized by DoD for that purpose.
  • 2D-Matrix – is a machine-readable two-dimensional barcode that includes the UII along with data identifiers and separators that allow computer systems to easily break the UII into its various components in an entirely unambiguous fashion.
  • Direct-Part Mark – is a process to permanently mark parts with their UII in a manner that is more reliable than a label or plate affixed to the item. These methods include dot peening, engraving, laser etching, embroidering and others.
  • IUID Registry– is a system of maintaining and transacting with the Government database holding records for each uniquely identified item. It works closely with the Wide Area Workflow (WAWF) system to ensure that costly or serially managed items purchased by the Government are registered and that the custody of items is properly attributed.
  • Virtual IUID – refers to the UII that should have been applied to an item, or would have been applied, had the item been acquired after UID marking was contractually required for the item. It is generally attributed to items whose known markings include CAGE, Part Number and Serial Number, allowing them to be unambiguously identified. Virtual IUIDs allow for such items to be represented in the IUID Registry and are often physically marked when returned to a central location for storage, service or maintenance. Some assets that will never be seen again, such as satellites, may be given a virtual IUID so that they may be recognized in audits.

What is a UII (or IUID)?

For DoD Item Unique Identification, the UII (/IUID) is the string of up to 50 characters that uniquely identifies an item on a global scale. It includes at a minimum, the identifier of the entity that issued the UII and a sequence number. Depending on the construct or methodology, more information may be included to enhance the usability of the UII. At a minimum, the UII also includes a code that identifies the type of Entity Identifier used.

The DoD IUID system supports several methods of methodologies for building UIIs, based on specific needs and circumstances. The two most prevalent are the Construct 1 and Construct 2. Before defining them, it helps to understand their first two components.

UII Entity ID

The Entity ID (EID) is one of the things that keep identifiers unique. Every defense contractor could assign a given serial number, say ‘00001’, which would hardly be unique. However, adding their company ID in front of it, would do that, provided they issued one of every IUID serial number. More about that later. The three most popular Entity IDs are:

  • CAGE Code (D) – issued by the Government to identify commercial entities it does business with
  • DUNS (UN) – a number issued by Dunn and Bradstreet to unique identify businesses
  • DODAAC (LD) – the DOD Automated Address Code that identifies defense activities

Issuing Agency Code (IAC)

The IAC identifies the agency that issued the Entity ID, shown in parentheses in the above list. The IAC indicates what portion of the UII is the Entity ID. For example, looking at the UII D1HLD9ABCDE000001, we recognize that the D indicates a CAGE code, and thus the next five characters are a CAGE code and the rest are part of the UII. Conversely, UII LDX092H1ABCDE000001 indicates a UII belonging to DODAAC X09H1.

Construct 2 UII

A Construct 2 UII consists of four parts:

  • Issuing Agency Code, identifying the type of Entity ID in use
  • Entity ID, such as the CAGE, DUNS or DODAAC of the entity managing the serial number
  • Part Number of the item
  • Serial Number of the part (unique within the Part Number)

Construct 2 is commonly used, largely because it does not require any management of the serial number portion beyond what a company would already have in place to manage the serial numbers it assigns to parts.

Construct 1 UII

Construct 1 consists of a serial number that is issued by an entity that is unique across all items, rather than with regard to a specific part number.

  • Issuing Agency Code, identifying the type of Entity ID in use
  • Entity ID, such as the CAGE, DUNS or DODAAC of the entity managing the serial number
  • Serial Number of the part (unique across all UIIs issued by the Entity)

There at least a couple of reasons one might choose to use Construct 1:

  • Parts manufactured by a subcontractor where the prime contractor cannot guarantee the reliability of their serial number management.
  • It is desirable to hide the part number of the item

The downside of Construct 1 is that the entity must have a system in place to manage the UII serial numbers and correlate them to parts and their serial numbers. With Construct 2 one can determine the item’s part number by looking at the UII, and from that the item’s serial number. And, they rely on the manufacturer’s existing serial number management systems to ensure uniqueness.

Data Matrix (2D) Symbol vs UII

IUID Data Matrix
IUID MRI (Data Matrix)

UIIs appear in two forms, human-readable and machine-readable, although that distinction is a little blurred by use.  The 2D Data Matrix symbol includes delimiters that allows automated systems to determine that the symbol is an IUID and also determine the individual components of the symbol.  The term Machine-Readable Interface (MRI) refers to both the encoded UII and the data structure of the Data Matrix symbol as defined by Mil-Std-130N.

The UII is just the data without any encoding. The example below shows how delimiters and data identifiers in the Data Matrix’s MRI assist automated systems understand exactly the components of the UII encoded in the symbol.

UII:   D1HLD9ABCDE000001

MRI: [)> RS 06 GS 17V 1HLD9 GS 1P ABCDE GS S000001 RS EOT

In the MRI, “[)>RS06” tells a reader to expect a machine-readable content that includes data identifiers in the stream, in this case a 17V (CAGE), 1P (part number) and S (serial number).

UIIs that appear without any encoding are referred to as Concatenated UIIs. This is the form that UIIs are most often communicated in, such as when submitted to WAWF at time of acquisition. However, WAWF still wants to know how the IUID may be broken down, so it requires that the serial number portion be communicated as well.

This is also true of IUIDs as found in the 2D PDF417 symbol that appears on the Mil-Std-129 Exterior Container Label, but in their Concatenated UII form, as indicated by the 25S Data Identifier.

PDF417 UID: … GS 25S D1HLD9ABCDE000001GS S 000001 …

The UII is followed by its serial number component, indicated by the S data identifier. By knowing the serial number component and the IAC, one can determine if where the Entity ID ends and the Serial Number begins. Anything in between would be the Part Number, making the UII a Construct 2.

Read more from the IUID Program Office:  Item Unique Identification – The Basics.