ECP is designed to provide the opportunity for Marines who have earned a four-year degree before joining the Corps or during active duty to serve as Marine Corps officers. Marines successfully completing the program receive a commission as a second lieutenant. ECP is open to all active duty enlisted Marines and members of the Marine Corps Reserve who meet the eligibility requirements ( Link is listed below ).
MECEP is designed to provide outstanding enlisted marines the opportunity to serve as Marine Corps officers. Marines successfully completing the program receive a baccalaureate degree and a commission as a second lieutenant. MECEP is open to all active duty enlisted marines and members of the Marine Corps reserve assigned to the Active Reserve (AR) program who meet the eligibility requirements ( Link is listed below ).
LDO Program is designed to provide technically oriented officers to perform duties that are limited to specific MOS(s), require authority and responsibility greater than that normally expected of a WO, require strong managerial skills, and are outside the normal development pattern for unrestricted officers or for which no unrestricted officers are available. Applicants must be technically and professionally qualified to serve in the MOS(s) to which applying and meet the eligibility requirements ( Link is listed below ).
WO Program is designed to provide the Marine Corps with technical specialists who perform duties that require extensive knowledge of a particular military occupational specialty (MOS) and who can be assigned to successive tours of duty in their primary MOS. Applicants must be technically and professionally qualified to serve in the MOS(s) to which applying and meet the eligibility requirements ( Link is listed below ).
http://www.mcrc.marines.mil/UnitHome/OfficerPrograms.aspx