The United States Army uses various personnel management systems to classify soldiers in different specialties which they receive specialized and formal training on once they have successfully completed Basic Combat Training (BCT). Commissioned officers are classified by their area of concentration, or AOC. Just like enlisted MOSCs, AOCs are two digits plus a letter. Related AOCs are grouped together by specific branch of the Army or by broader in scope functional areas (FA). Typically, an officer will start in an AOC of a specific branch and move up to an FA AOC.