Unit Identification Code

The Unit Identification Code (UIC) is a six character alphanumeric code that uniquely identifies each United States Department of Defense entity.

The first character is the Service Designator:

The next three characters indicate the Parent Unit Designator. These vary from branch to branch and provide information about the type of unit. For example, in the US Army, the parent unit designation breaks down as such:

The final two characters indicate the Descriptive Designator. They describe the specifics characteristics of the unit. For example, the parent Battalion unit for the Army will use "AA." A child Company unit, such as A Company, will use "A0."

...
Wikipedia