The term reserve component (RC) refers collectively to the seven individual reserve components of the Armed Forces: (1) the Army National Guard; (2) the Army Reserve; (3) the Navy Reserve; (4) the Marine Corps Reserve; (5) the Air National Guard (6) the Air Force Reserve; and (7) the Coast Guard Reserve. The Space Force, under the Department of the Air Force, does not have a reserve component (10 U.S.C. §20001).
The purpose of these seven reserve components, per 10 U.S.C. §10102, is to "provide trained units and qualified persons available for active duty in the armed forces, in time of war or national emergency, and at such other times as the national security may require, to fill the needs of the armed forces whenever more units and persons are needed than are in the regular components." The Army and Air National Guards also have an important role under state authority, responding to various emergencies such as disasters and civil disorders.
Military policy describes the reserve components as an "operational force," elaborating that
The RCs provide operational capabilities and strategic depth to meet U.S. defense requirements across the full spectrum of conflict... In their operational roles, RCs participate in a full range of missions according to their Services' force generation plans. Units and individuals participate in missions in an established cyclic or periodic manner that provides predictability for the combatant commands, the Services, Service members, their families, and employers. In their strategic roles, RC units and individuals train or are available for missions in accordance with the national defense strategy. As such, the RCs provide strategic depth and are available to transition to operational roles as needed.
The use of the RC increased after 1991. From 1986 to 1990, the reserve components contributed approximately 3,000 person-years of active service. This increased to an annual average of 35,000 person-years from 1996-2001. From 2002 to 2010 (including part of the conflicts in Iraq and Afghanistan, along with domestic and foreign counterterrorism actions), the RC contributed an annual average of 146,000 person-years domestically and globally. CRS has not found person-year figures for years after 2010.
The Army Reserve, Navy Reserve, Marine Corps Reserve, Air Force Reserve, and Coast Guard Reserve are exclusively federal organizations. There are 54 separate National Guard organizations: one for each state, and one each for Puerto Rico, Guam, the U.S. Virgin Islands, and the District of Columbia (DC). While the DC National Guard is an exclusively federal organization and operates under federal control at all times, the other 53 National Guards operate as state or territorial organizations most of the time. In this capacity, each of these organizations is identified by its state or territorial name (e.g., the California National Guard or the Puerto Rico National Guard) and is controlled by its respective governor. National Guard units and personnel can be ordered into federal service. When this happens, control of the affected units and personnel passes from the state governor to the President of the United States.
The Ready Reserve is the primary manpower pool of the reserve components. Members of the Ready Reserve are typically called to active duty before members of the Standby Reserve or the Retired Reserve. The Ready Reserve is made up of three subcomponents:
The Selected Reserve contains those units and individuals within the Ready Reserve designated as "so essential to initial wartime missions that they have priority over all other Reserves." (see Table 1).
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Reserve Component |
Selected Reserve |
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Army National Guard |
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Army Reserve |
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Navy Reserve |
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Marine Corps Reserve |
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Air National Guard |
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Air Force Reserve |
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Total |
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Note: These figures reflect the number of personnel in each of the reserve components as of September 30, 2025.
Source: Department of Defense, Defense Manpower Data Center, Selected Reserve Personnel by Reserve Component and Rank/Grade, September 2025.
Members of the Selected Reserve are generally required to perform one weekend of training each month and two weeks of training each year, although some may train more than this. When reservists are activated, they most frequently come from this category.
The Individual Ready Reserve (IRR) is a manpower pool of individuals who have already received military training, either in the Active Component or in the Selected Reserve. They are not normally required to perform training, but can be ordered to active duty under certain circumstances. The Inactive National Guard (ING) is, for practical purposes, the National Guard equivalent of the IRR. There is currently no ING for the Air National Guard.
The Standby Reserve contains those individuals who have a temporary disability or hardship and those who hold key positions in their civilian jobs. They are not required to participate in military training and may only be ordered to active duty in limited circumstances.
The Retired Reserve includes Reserve personnel who are qualified for reserve retirement. Members of the Retired Reserve may be ordered to active duty only in limited circumstances.
Reserve units are primarily filled by traditional reservists: members of the Selected Reserve who are usually required to work one weekend a month and two weeks a year. However, many reserve units are also staffed by one or more full-time civilian and/or military employees. These employees, known as full-time support (FTS) personnel, are "assigned to organize; administer; instruct; recruit and train; maintain supplies, equipment, and aircraft; and perform other functions required on a daily basis in the execution of operational missions and readiness preparation." (DOD Instruction 1205.18)
There are four statutory provisions by which members of the National Guard and Reserve can be involuntarily ordered to federal active duty for a year or more.
These are commonly referred to as Full Mobilization (10 U.S.C. §12301(a)), Partial Mobilization (10 U.S.C. §12302), and Presidential Reserve Call-up (10 U.S.C. §12304), and activation in support of pre-planned missions for the Combatant Commands (10 U.S.C. §12304b). These provisions differ from each other in terms of the statutory requirements for utilization, the number and category of reservists authorized for call up, and the duration of the call up. Another authority added in 2011, provides for involuntarily activating members of the Army Reserve, Navy Reserve, Marine Corps Reserve, and Air Force Reserve to respond to major disasters or emergencies, for periods of up to 120 days (10 U.S.C. §12304a).
In addition to activations under federal authority, members of the National Guard can also be activated by their governors for full-time duty (i.e., state active duty) owing to their unique state/federal status. They can also be activated under state control but with pay and benefits provided by the federal government. This is sometimes referred to as Title 32 status in reference to the part of the United States Code that governs this duty status.
Reservists' pay and benefits may vary significantly based on the type of duty performed. Some key variables in determining the compensation provided include (1) whether an individual is performing active duty or inactive duty; (2) if on active duty, the statutory authority under which the individual is activated, the duration of the duty, and whether the duty performed is in support of a contingency operation; and (3) for the National Guard, whether the duty is in a state status or federal status.
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Relevant Statutes |
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CRS Products CRS Report RL30802, Reserve Component Personnel Issues: Questions and Answers CRS Report R43808, Army Active Component (AC)/Reserve Component (RC) Force Mix: Considerations and Options for Congress |