Defense Primer: Reserve Forces

Defense Primer: Reserve Forces

Defense Primer: Reserve Forces

Updated June 13, 2025 (IF10540)

The term reserve component (RC) refers collectively to the seven individual reserve components of the Armed Forces. Congress exercises authority over the reserve components under its constitutional authority "to raise and support Armies," "to provide and maintain a Navy," to "provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions", and "to provide for organizing, arming, and disciplining the Militia," (Article I, Section 8).

There are seven reserve components:

Army National Guard

Army Reserve

Navy Reserve

Marine Corps Reserve

Air National Guard

Air Force Reserve

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, as codified in law, 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." (10 U.S.C. §10102) The Army National Guard and the Air National Guard also have an important role under state authority, responding to various emergencies such as disasters and civil disorders.

Difference between Federal Reserves and National Guard

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. While the District of Columbia 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 passes from the governor of the affected units and personnel to the President of the United States.

Reserve Categories

All reservists, whether they are in the Reserves or the National Guard, are assigned to one of three major reserve categories: the Ready Reserve, the Standby Reserve, or the Retired Reserve.

Ready Reserve

The Ready Reserve is the primary manpower pool of the reserve components. Members of the Ready Reserve will usually be 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." (DOD Instruction 1215.06.) 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 (see Table 1).

Table 1. Selected Reserve Personnel Strength

As of April 30, 2025

Reserve Component

Selected Reserve

Army National Guard

328,171

Army Reserve

170,759

Navy Reserve

57,691

Marine Corps Reserve

32,970

Air National Guard

104,855

Air Force Reserve

65,596

Total

760,042

Source: Department of Defense, Defense Manpower Data Center, Selected Reserve Personnel by Reserve Component and Rank/Grade, April 2025.

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 made up of those members of the Army National Guard who are in an inactive status (currently there is no ING for the Air National Guard). The ING is, for practical purposes, the National Guard equivalent of the IRR.

There are just over 1 million total members of the Ready Reserve.

Standby Reserve

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.

Retired Reserve

The Retired Reserve includes Reserve personnel who are receiving retired pay or who transfer into the Retired Reserve after qualifying for reserve retirement, but before becoming eligible to receive retired pay. Members of the Retired Reserve may be ordered to active duty only in limited circumstances.

Full-Time Support

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).

Activations

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. Three of these authorities have existed for decades, and 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). The fourth authority, added in 2011, allows reservists to be activated to support the Combatant Commands for preplanned missions (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 called 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 governor 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.

Pay, Benefits, and 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.

Relevant Statutes

Title 10, U.S. Code, Subtitle E (Reserve Components)

Title 32, U.S. Code (National Guard)

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