A US military officer is a member of the United States armed forces who has earned an officer's commission in the hierarchical system of leadership — enlisted personnel, non-commissioned officers and commissioned officers — that characterizes most military organizations. The US maintains five armed services: the Army, the Navy, the Marines, the Air Force and the Coast Guard. Each of these services has many thousands of members, organized into various fighting and support units, each commanded by one or more officers, depending upon the size of the unit. US military officers, while trained and qualified by the service they're joining, are technically appointed by the president of the United States.
All US military officers are college graduates. The core of the US military officer corps is drawn from the five service academies: the US Military Academy at West Point, NY; the US Naval Academy in Annapolis, Md.; the US Coast Guard Academy in New London, Ct.; the US Air Force Academy in Colorado Springs, Co.; and the US Merchant Marine Academy at Kings Point, NY. These are four-year colleges that offer rigorous military training, as well as a thorough college education, and confer a bachelor's degree as well as a commission as a second lieutenant or ensign, as appropriate.
The majority of US military officers, however, graduate from the thousands of civilian colleges and universities nationwide that partner with the services to offer Reserve Officers Training Corps (ROTC) programs. These students graduate with civilian degrees as well as military commissions.
The services also identify some enlisted members as potential officers as well. Those with college degrees will be assigned to Officers Candidate School (OCS). Enlisted personnel without degrees may be permitted by their service to attend college and earn a degree, following which they're sent to OCS.
Some US military officers are directly commissioned into professional branches of their service. Military lawyers, for example, are fully credentialed civilian lawyers upon application for commissioning as an officer in the Judge Advocate General's (JAG) Corps, and doctors generally complete all academic and licensing requirements before application for commissions in one of the services' Medical Corps. These officers generally are commissioned as as captains in the Army, Air Force or Marines, or as lieutenants in the Navy and Coast Guard.
Officers receive essentially the same Basic Combat Training as enlisted personnel, as well as leadership training, to prepare them for their commands. Upon successful completion of their training and their college degrees, which may take place concurrently, they're commissioned as officers, usually at the lowest rank of their service: ensign in the Navy and Coast Guard, and second lieutenant in the Army, Air Force and Marines. The newest ensign or second lieutenant rates a salute from all enlisted and non-commissioned officers, and outranks even the most senior non-commissioned officers. It's not recommended, however, that such officers actually pull rank on the sergeants and petty officers who are responsible for the day-to-day operation of the armed services.
A newly commissioned US military officer will be assigned to one of a wide variety of duties, depending on the branch of service they're assigned to. Rotated through a number of duty assignments, they'll be exposed to the many responsibilities expected of a US military officer, as well as getting to enjoy the associated benefits and military discounts. During each assignment, their superiors will have the opportunity to evaluate their leadership potential and fitness for greater responsibility and authority.
The US military recognizes three types of officers. The highest-ranking group is general or flag officers, the generals and admirals that command large military organizations like divisions and fleets that can be expected to act autonomously over extended periods of time. General and flag officers are recommended by the president and confirmed by the US Senate. Field grade or senior officers, which command smaller units like regiments and brigades that may act autonomously for limited periods of time, are colonels, lieutenant colonels and majors in the Army, Air Force and Marines; and captains, commanders and lieutenant commanders in the Navy and Coast Guard. The lowest three ranks – second and first lieutenants and captains in the Marines, Army and Air Force; and ensigns, lieutenants junior grade and lieutenants in the Navy and Coast Guard, are referred to as company grade or junior grade officers, respectively.
Upon achieving certain milestones of service, a US military officer is eligible for promotion to the next higher rank. Promotion in the US military is highly competitive and based on seniority only to the extent that a minimum length of time must be served in each rank before becoming eligible for promotion to the next rank. Promotions are based on merit and experience, and under the US military's "up or out" policy, officers who are twice passed over for promotion are expected to leave the service or retire.