In the United States Army, United States Air Force, and United States Marine Corps, general is a four-star general officer, with the pay grade of O-10. The United States Army is a military organization whose primary mission is to "provide necessary forces and capabilities. An officer of 4 star rank is a very senior commander in many of the armed services holding a rank described by the NATO code of OF-9. General ranks above lieutenant general and below General of the Army or General of the Air Force; the Marine Corps does not have an established grade above general. This article is about a United States military rank For other countries that use a similar rank see Lieutenant General. General of the Army (GA is a five-star General officer and is the highest possible rank in the United States Army. General of the Air Force (GOAF is a five-star General officer rank and is the highest possible rank in the United States Air Force. General is equivalent to an admiral in the other uniformed services. Please see " Admiral " for other nations which use this rank In the United States Navy, the United States Coast Guard and the The United States has seven federal uniformed services that commission officers as defined by Title 10, and subsequently structured and organized Since the grade of General of the Army and General of the Air Force are reserved for war-time use only, and since the Marine Corps has no five-star equivalent, a four-star general is currently considered to be the highest appointment an officer can achieve in these three services.
The U.S. Code of law explicitly limits the total number of four-star generals that may be on active duty at any given time. The United States Code ( USC) is a compilation and Codification of the general and permanent federal Law of the United States. The total number of active duty general officers is capped at 302 for the Army, 279 for the Air Force and 80 for the Marine Corps.  For the Army and Air Force, no more than 16. 3% of the service's active duty general officers may have more than two stars, and no more than 25% of those may have four stars.  This corresponds to 12 four-star Army generals, 11 four-star Air Force generals and 3 four-star Marine generals.
Some of these slots are reserved by statute. For the Army and Air Force, the Chief of Staff and the Vice Chief of Staff are both four-star generals; for the Marine Corps, the Commandant and the Assistant Commandant are both four-star generals. The Chief of Staff of the United States Army ( CSA) is the highest ranking officer in the United States Army and is member of the Joint Chiefs of Staff The Vice Chief of Staff of the United States Army ( VCSA) is the principal advisor and assistant to the Army Chief of Staff. The Commandant of the Marine Corps ( CMC) is the highest ranking officer in the United States Marine Corps and is a member of the Joint Chiefs of Staff The Assistant Commandant of the Marine Corps ( ACMC) is the second highest ranking officer in the United States Marine Corps.
There are several exceptions to these limits allowing more than allotted within the statute. A four-star officer serving as Chief of Staff to the President, or as Chairman or Vice Chairman of the Joint Chiefs of Staff does not count against his service's general or flag officer cap. The Chairman of the Joint Chiefs of Staff ( CJCS) is by law the highest ranking military officer overall in the United States Armed The Chairman of the Joint Chiefs of Staff ( CJCS) is by law the highest ranking military officer overall in the United States Armed The Vice Chairman of the Joint Chiefs of Staff ( VJCS) is by law the second highest ranking military officer overall in the United States Armed Forces ranking The Joint Chiefs of Staff ( JCS) is a group comprising the Chiefs of service of each major branch of the Armed services in the United States armed forces An officer serving in one of several joint positions does not count against his service's four-star limit, but he does count against his service's limit on officers with more than two stars; these positions include the commander of a unified combatant command, the commander of U.S. Forces Korea, and the commander of U.S. European Command (but only if the commander is also the Supreme Allied Commander, Europe). A Unified Combatant Command ( UCC) is a United States joint military command composed of forces from two or more services has a broad and continuing mission United States Forces Korea ( USFK) refers to the ground air and naval divisions of the United States Armed Forces stationed in South Korea. Composition The main combat power of EUCOM is formed around the US Seventh Army, US Sixth Fleet and Third Air Force. Supreme Allied Commander is the title held by the most senior commander within certain multinational military alliances  Officers serving in certain intelligence positions are not counted against either limit, including the Director of the Central Intelligence Agency. Director of the Central Intelligence Agency ( D/CIA) serves as the head of the Central Intelligence Agency, which is part of the United States Intelligence  The President may also add four-star slots to one service if they are offset by removing an equivalent number from other services. Finally, all statutory limits may be waived at the President's discretion during time of war or national emergency. 
Four-star grades go hand-in-hand with the positions of office they are linked to, so these ranks are temporary. Officers may only achieve four-star grade if they are appointed to positions that require the officer to hold such a rank.  Their rank expires with the expiration of their term of office, which is usually set by statute.  Four-star generals are nominated for appointment by the president from any eligible officers holding the rank of brigadier general or above, who also meet the requirements for the position, under the advice and/or suggestion of their respective department secretary, service secretary, and if applicable the joint chiefs. The President of the United States is the Head of state and Head of government of the United States and is the highest political official in United States by  For some specific positions, statute allows the President to waive those requirements for a nominee whom he deems would serve national interests.  The nominee must be confirmed via majority vote by the Senate before the appointee can take office and thus assume the rank. The United States Senate is the Upper house of the bicameral United States Congress, the Lower house being the House of Representatives  The standard tour length for most four-star positions is three years, bundled as a two-year term plus a one-year extension, with the following exceptions:
Note: Extensions of the standard tour length can be approved, within statutory limits, by their respective service secretaries, the Secretary of Defense, the president, and/or Congress but these are rare, as they block other officers from being promoted. Some statutory limits under the U. S. Code can be waived in times of national emergency or war. Four-star ranks may also be given by act of Congress but this is extremely rare.
Four-star officers must retire after five years in grade or 40 years of service, whichever is later, and all general officers must retire the month after their 64th birthday.  However, the Secretary of Defense can defer a four-star officer's retirement until the officer's 66th birthday and the President can defer it until the officer's 68th birthday.
General officers typically retire well in advance of the statutory age and service limits, so as not to impede the upward career mobility of their juniors. Since only a finite number of four-star slots are available to each service, typically one officer must leave office before another can be promoted.  Maintaining a four-star rank is a game of musical chairs; once an officer vacates a position bearing that rank, he has 60 days to find another job of equal importance before he must retire.  Historically, officers leaving four-star positions were allowed to revert to their permanent two-star ranks to mark time in lesser jobs until statutory retirement, but now such officers are expected to retire immediately to avoid obstructing the promotion flow.
To retire at four-star grade, an officer must accumulate at least three years of satisfactory active duty service in that grade, as certified by the Secretary of Defense and confirmed by the Senate.  The Secretary of Defense may reduce this requirement to two years, but only if the officer is not being investigated for misconduct. Officers who do not meet the service-in-grade requirement revert to the next highest grade in which they served satisfactorily for at least six months. It is extraordinarily rare for a four-star officer not to be nominated to retire in grade, or for such a nomination not to be confirmed by the Senate unanimously.
Four-star officers typically step down from their posts up to 60 days in advance of their official retirement dates. Officers retire on the first day of the month, so once a retirement month has been selected, the relief and retirement ceremonies are scheduled by counting backwards from that date by the number of days of accumulated leave remaining to the retiring officer. During this period, termed transition leave or terminal leave, the officer is considered to be awaiting retirement but still on active duty.