Commissioned naval officers originate from the United States Naval Academy, the United States Merchant Marine Academy, other Service Academies (United States Military Academy, United States Coast Guard Academy, or United States Air Force Academy), Naval Reserve Officer Training Corps (NROTC), Officer Candidate School (OCS), the since-disestablished Aviation Officer Candidate School (AOCS), and a host of other commissioning programs such as the "Seaman to Admiral-21" program and the limited duty officer/chief warrant officer (LDO/CWO) selection program.