High Quality Content by WIKIPEDIA articles! The United States Marine Corps Officer Candidates School (OCS) is the entry-level training for Marine officers, equivalent to recruit training for enlisted Marines. Located at Marine Corps Base Quantico, the school trains, screens, and evaluates potential Marine Corps officers. 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.