Officer Candidate School (United States Army)

The United States Army's Officer Candidate School (OCS) is an officer training program that trains, assesses, and evaluates potential commissioned officers of the U.S. Army, U.S. Army Reserve, and Army National Guard. Officer Candidates are former enlisted members (E-4 to E-8), Warrant Officers, inter-service transfers, or civilian college graduates who have enlisted as an "09S" to attend OCS after they have completed Basic Combat Training (BCT).

Source: Wikipedia — Officer Candidate School (United States Army) (CC BY-SA 4.0)