The Army is the U.S. military's primary ground force. Title 10, Subtitle B, Part I, Chapter 707, of the U.S. Code addresses the organization of the Army. The Marine Corps serves as the Navy's ground-focused fighting force. Title 10, Subtitle C, Part I, Chapter 807, Section 8063, addresses Marine Corps composition and functions.
The Congressional Budget Office's (CBO's), The U.S. Military's Force Structure: A Primer, 2021 Update, notes
The Army and Marine Corps are generally organized as hierarchies of units, with each type of unit commanded by a noncommissioned or commissioned officer of a specific rank. These units are described from smallest to largest.
CBO further describes such units, from smallest to largest, in part as follows (with certain additional information provided by CRS in brackets):
Squad/Team/Section. A squad is led by a sergeant and consists around 4 to 12 personnel. [Squads can be further divided into teams or sections.]
Platoon. A platoon is [led in the Army or commanded in the Marines] by a lieutenant and includes from 16 to 50 personnel. Heavy platoons have armored vehicles (such as tanks or infantry fighting vehicles, depending on platoon type).
Company/Troop/Battery. A company is commanded by a captain and includes two to five subordinate platoons (usually three or four). It has about 60-200 personnel. Cavalry [air or ground] companies are called troops [Army only]; artillery [and air and missile defense] companies are called batteries.
Battalion/Squadron. A battalion is commanded by a lieutenant colonel and usually includes three to five combat companies and a support company. It has about 400-1,000 personnel. Cavalry battalions are called squadrons.
Brigade Combat Team/Support Brigades/ Regiment/Group. An [Army] brigade is commanded by a colonel and generally configured as a brigade combat team (BCT) or a support brigade. A BCT has about 4,000-4,700 personnel, depending on [type]. [Army] cavalry brigades are called regiments; some types of support brigades are called groups. Marine Corps units at this level also are called regiments. (The term Marine Expeditionary Brigade [MEB] refers to a [regimental-size] task force which is larger [than an Army BCT].
Division. An [Army] division is commanded by a major general and includes two to five BCTs (usually four), an aviation brigade, an artillery brigade, an engineer brigade, and a logistics brigade. [Army] divisions consist of 12,000-16,000 personnel. [Marine divisions are also commanded by major generals. Each Marine division has three infantry regiments and one artillery regiment and consists of about 20,000 personnel.]
Corps. Corps are commanded by a lieutenant general and include two to five divisions and numerous support brigades and commands. [Army] corps have about 40,000-100,000 personnel. The Marines do not have designated corps, although a Marine Expeditionary Force (MEF) is similar in size and also is commanded by a lieutenant general.
Army. An army is the highest command level in a given theater of operations and typically has 100,000-300,000 personnel. It is an element of a joint command structure; the Army's component is commanded by a general. An Army's operational theater is established to support one or more corps ... and includes numerous support brigades and support commands.
According to the CBO's The U.S. Military's Force Structure: Fiscal Year 2024 Update to Personnel Numbers and Costs, and its Interactive Force Structure Tool (May 2025), Army brigades are organized as follows.
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The Brigade Combat Team (BCT) is the Army's basic combined-arms tactical force of about 4,000 soldiers. The Army currently has 59 BCTs, with 32 BCTs in the Active Component (AC) and 27 BCTs in the Army National Guard (ARNG). There are three types of BCTs: Infantry BCTs (IBCTs), Armored BCTs (ABCTs), and Stryker BCTs (SBCTs). In May 2025, the Army decided to transform all IBCTs into Mobile Brigade Combat Teams (MBCT) to enhance maneuverability and survivability. Infantry BCTs (IBCTs) include three infantry battalions, a reconnaissance and surveillance cavalry squadron, a field artillery battalion, a brigade engineer battalion, and a logistics support battalion. IBCTs also are organized to be airborne or air-assault capable. The Army currently has 14 AC and 20 ARNG IBCTs. Armored BCTs (ABCTs) include three armor/mechanized infantry battalions, an armed reconnaissance cavalry squadron, a field artillery battalion, a logistics support battalion, and a brigade engineer battalion. The Army currently has 11 AC and five ARNG ABCTs. Stryker BCTs (SBCTs) are equipped with the Stryker, an eight-wheel-drive, light-armored vehicle. SBCTs consist of three infantry battalions, a cavalry squadron for reconnaissance and target acquisition, a field artillery battalion, a brigade support battalion, a brigade engineer battalion, a military intelligence company, an engineer company, a signal company, an antitank company, and a headquarters company. The Army currently has seven AC and two ARNG SBCTs. Under the Army's Transformation Initiative, one ARNG SBCT is to transform into a MBCT. Functional Support Brigades (FSBs) FSBs are designed to plug into operational formations at the Army Service Component Command (ASCC), corps, division, or theater level. There are several types of FSBs, including air defense, artillery, engineers, military police, cyber, signal, explosive ordinance disposal, medical support, and aviation. Multifunctional Support Brigades (MFSBs) Similar to FSBs, MFSBs are designed to plug into operational formations, but their purpose is to support BCTs. There are five types of MFSBs: combat aviation, combat support, sustainment, fires and battlefield surveillance, and tactical-level task and support. Security Force Assistance Brigades (SFABs) SFABs are capable of conducting Security Force Assistance operations. The Army has six regionally focused SFABs—five in the AC and one in the Army ARNG. Reportedly, as part of the Army's Transformation Initiative, one ARNG SFAB and one AC SFAB are to be eliminated. Multi-Domain Task Force (MDTF) MDTFs are brigade-sized units capable of synchronizing precision effects and precision fires in all domains against adversary anti-access/area denial (A2/AD) networks. The Army plans to establish five AC MDTFs. |
The Marines organize its forces into task forces, each with a command, ground combat, aviation combat, and logistics combat element. The largest task force, a Marine expeditionary force (MEF), includes a ground combat division, an air wing, and a support group. The active component of the Marine Corps has three MEFs, including a total of three divisions, three air wings, and three logistics groups. The Marine Corps Reserve contains one division, one air wing, and one support group. According to the Marines, for FY2026, the Marine Corps will have 19 AC infantry battalions as well as two AC Littoral Combat Teams (LCTs) assigned to Marine Littoral Regiments (MLRs). There are currently eight RC infantry battalions. The Marines organize operational forces as follows:
The MAGTF is the Marine Corps' principal organizational construct for conducting military operations. MAGTFs consist of ground, air, logistics, and cyberspace assets under a central command. There are three types of MAGTFs: the Marine Expeditionary Force (MEF), the Marine Expeditionary Brigade (MEB), and the Marine Expeditionary Unit (MEU).
According to the Marine Corps, the MEF is the primary warfighting force for larger operations and consists of 46,000-90,000 Marines. There are three active MEFs stationed in California, North Carolina, and Japan. Commanded by a Lieutenant General, MEFs are composed of a Marine Division, a Marine Aircraft Wing, and a Marine Logistics Group.
MEBs are task organized for specific missions and consist of 4,000-16,000 Marines. MEBs, commanded by a Brigadier General, have firepower and aviation assets and are composed of a regimental-size Ground Combat Element, an Aircraft Group, and a Combat Logistics Regiment.
MEUs are forward deployed on Navy ships and are often first to arrive at a crisis. MEUs consist of approximately 2,200 Marines and are commanded by a Colonel. MEUs are composed of a Battalion Landing Team; a Composite Helicopter Squadron; and a Combat Logistics Battalion.
MLRs are intended to operate and survive in a contested maritime environment and designed to control local air space, choke points, or waterways. MLRs are to consist of about 1,800 to 2,000 Marines and Sailors, and composed of three main elements: a Littoral Combat Team (LCT), a Littoral Anti-Air Battalion, and a Combat Logistics Battalion. The Marines plan to establish two MLRs and, under the 2025 Force Design update, no longer plan to convert a third regiment into an MLR.
Related CRS Products
CRS Report R48606, 2025 Army Transformation Initiative (ATI) Force Structure and Organizational Proposals: Background and Issues for Congress, by Andrew Feickert.
CRS In Focus IF10675, Army Security Force Assistance Brigades (SFABs), by Andrew Feickert.
CRS In Focus IF11797, The Army's Multi-Domain Task Force (MDTF), by Andrew Feickert.
CRS In Focus IF12200, The U.S. Marine Corps Marine Littoral Regiment (MLR), by Andrew Feickert.
CRS Report R47614, U.S. Marine Corps Force Design Initiative: Background and Issues for Congress, by Andrew Feickert.