The United States Marine Corps Officer Candidates School (OCS) is a training regiment designed to screen and evaluate potential Marine Corps Officers. Those who successfully complete the period of instruction are commissioned as Second Lieutenants in the United States Marines. Unlike the other United States military services, the majority of Marine Corps officers complete OCS to earn a commission; the exceptions are midshipmen from the United States Naval Academy, limited duty officers, and inter-service transfers. It is located at Marine Corps Base Quantico.