Structure of the United States Army
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The Structure of the United States Army is complex, and able to be seen in several different ways: active/reserve, operational/administrative, and headquarters/field.
This page aims to portray the current central structure of the US Army, perhaps in the future the former central structure (including Army Ground Forces, Army Service Forces, and Army Air Forces) and both present and historical combat formations (armies, corps, and brigades).
Active and Reserve 
The United States Army is made up of three components: one active—the Regular Army; and two reserve components—the Army National Guard and the Army Reserve. Both reserve components are primarily composed of part-time soldiers who train once a month, known as Battle Assembly or Unit Training Assemblies (UTAs), and conduct two to three weeks of annual training each year. Both the Regular Army and the Army Reserve are organized under Title 10 of the United States Code. The National Guard is organized under Title 32. While the Army National Guard is organized, trained and equipped as a component of the U.S. Army, individual units are under the command of individual state's governors. However, units of the National Guard can be federalized by presidential order and against the governor's wishes.
During the First World War, the "National Army" was organized to fight the conflict. It was demobilized at the end of World War I, and was replaced by the Regular Army, the Organized Reserve Corps, and the State Militias. In the 1920s and 1930s, the "career" soldiers were known as the "Regular Army" with the "Enlisted Reserve Corps" and "Officer Reserve Corps" augmented to fill vacancies when needed.
In 1941, the "Army of the United States" was founded to fight the Second World War. The Regular Army, Army of the United States, the National Guard, and Officer/Enlisted Reserve Corps (ORC and ERC) existed simultaneously. After World War II, the ORC and ERC were combined into the United States Army Reserve. The Army of the United States was re-established for the Korean War and Vietnam War and was demobilized upon the suspension of the Draft.
Currently, the Army is divided into the Regular Army, the Army Reserve, and the United States National Guard. Prior to 1903 members of the National Guard were considered state soldiers unless federalized by the President. Since the Militia Act of 1903 all National Guard soldiers have held dual status: as National Guardsmen under the authority of the governor of their state and as a reserve of the U.S. Army under the authority of the President. Since the adoption of the total force policy, in the aftermath of the Vietnam War, reserve component soldiers have taken a more active role in U.S. military operations. Reserve and Guard units took part in the Gulf War, peacekeeping in Kosovo, and the 2003 invasion of Iraq.
Although the present-day Army exists as an all volunteer force, augmented by Reserve and National Guard forces, measures exist for emergency expansion in the event of a catastrophic occurrence, such as a large scale attack against the U.S. or the outbreak of a major global war.
The final stage of Army mobilization, known as "activation of the unorganized militia" would effectively place all able bodied males in the service of the U.S. Army. The last time an approximation of this occurred was during the American Civil War when the Confederate States of America activated the "Home Guard" in 1865, drafting all males, regardless of age or health, into the Confederate Army.
Operational and Administrative 
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Headquarters Department of the Army (HQ DA) Staff 
The U.S. Army is led by a civilian Secretary of the Army, who reports to the Secretary of Defense, and serves as civilian oversight for the U.S. Army Chief of Staff. The U.S. Army Chief of Staff is a member of the Joint Chiefs of Staff, a body composed of the service chiefs from each service who advise the President and Secretary of Defense on military matters under the guidance of the Chairman and Vice Chairman of the Joint Chiefs of Staff.
Field Operating Agencies 
- Assistant Secretary of the Army for Financial Management and Comptroller (ASA (FM&C))
- Cost and Economic Analysis Agency, MD
- Finance Command, VA
- Assistant Secretary of the Army for Manpower & Reserve Affairs (ASA (M&RA))
- EEO Agency, DC
- EEO Compliance and Complaints Review Agency, VA
- Assistant Secretary of the Army for Acquisition, Logistics, and Technology (ASA(ALT))
- Army Contracting Agency (ACA)
- Office of the Auditor General (SAAG)
- Office of the Chief of Public Affairs (OCPA)
- Soldiers Media Center
- Office of the Chief of Staff of the Army (OCSA)
- U.S. Army Test and Evaluation Management Agency, DC
- Center for Military Analysis, MD (not available)
- Center of Military History, DC
- U.S. Army Combat Readiness Center, Ala.
- Office of the Army G-8 (Financial Management)[nb 1]
- Center for Army Analysis, VA
- Office of the Army G-4
- Logistics Innovation Agency, VA
- Office of the Army G-3/5/7 (Operations/Plans)
- Army War College, PA
- Command and Control Support Agency, VA (not available)
- U.S. Military Observers Group, DC (not available)
- Office of the Deputy Chief of Staff for Personnel (Army G-1)
- Army Human Resources Command
- Office of the Assistant Chief of Staff for Installation Management (ACSIM)
- Installation Support Management Activity
- Office of the Judge Advocate General (OTJAG)
- The Judge Advocate General's Legal Center and School, VA
- U.S. Army Legal Services Agency, VA
Most U.S. Army units can be operationally divided into the following components from largest to smallest:
- Field army: Now primarily an administrative arrangement, consisting of multiple corps. The last time a multiple-corps army took the field was Third Army directing VII and XVIII Corps during Operation Desert Storm. Armies now also operate as Army Service Component Commands (ASCCs) of unified combatant commands, such as Seventh Army/USAREUR. Armies have also effectively operated as military districts formerly in the continental United States. Fifth Army and First Army performed this function up until recently.
- Corps: Formerly consisting of two or more divisions and organic support brigades, they are now termed an "operational unit of employment", that may command a flexible number of modular units. Usually commanded by a Lieutenant General. 20,000–45,000 soldiers.
- Division: Formerly consisted of three maneuver brigades, an artillery brigade, a division support command, an aviation brigade, an engineer brigade (in heavy divisions only) and other support assets. Until the Brigade Combat Team program was developed, the division was the smallest self-sufficient level of organization in the U.S. Army. Current divisions are "tactical units of employment", and may command a flexible number of modular units, but generally will include four brigade combat teams and a combat aviation brigade. Usually commanded by a Major General. 10,000–15,000 soldiers.
- Brigade (or group): Composed of two or more regiments/battalions, and commanded either by a Brigadier General or a Colonel (depending on whether the brigade is attached to a division or not), supported by a staff in a Headquarters and Headquarters Company. Since the Brigade Unit of Action program was initiated, maneuver brigades have transformed into brigade combat teams, generally consisting of two maneuver battalions, a cavalry squadron, a fires battalion, a special troops battalion (with engineers, signals, and military intelligence), and a support battalion. Stryker Brigade Combat Teams have a somewhat larger structure. 3,000–5,000 soldiers.
- Regiment: The Army, for the most part is no longer organized by Regiments. Rather, Battalions and Squadrons maintain Regimental Affiliations in that they are called (for example), 1st Battalion, 8th Infantry (Regiment is implied) and is written 1–8 Inf. In this case, there is no Regimental Commander and the Battalion is organized as part of a Brigade for combat. The exceptions are those units, such as Armored Cavalry Regiments which remain organized, and fight, as a Regiment and have a Regimental Commander. The written designation is easy to distinguish and commonly misused. A "/" separates levels of command. 1st Squadron, 3rd Armored Cavalry Regiment is written 1/3 ACR whereas the 1st Battalion, 6th Field Artillery (again, Regiment is implied) is written 1–6 FA.
- Battalion (or Cavalry Squadron): Normally composed of two to five (occasionally as many as eight) companies, troops or batteries and led by a Battalion/Squadron Commander, usually a Lieutenant Colonel supported by a staff in a Headquarters and Headquarters Company/Battery. 300–1,000 soldiers.
- Company (or artillery battery/cavalry troop): Designated A to C (plus HQ or support companies/batteries/troops) when in a 3 company/battery battalion or A to D when organized in a 4 company/battery battalion. Regimental Troops are designated A to T, depending on the number of Troops. The Troops are then divided into their like Squadrons. Each company/battery/troop is composed of three to four platoons and led by a Company/Battery/Troop Commander, usually a Captain supported by a First Sergeant. 62–190 soldiers.
- Platoon: Composed of two or more squads and led by a Platoon Leader, usually a Second Lieutenant supported by a platoon sergeant (Sergeant First Class). 20-50 soldiers.
- Section: Usually directed by a Staff Sergeant who supplies guidance for junior NCO Squad leaders. Often used in conjunction with platoons at the company level.
- Squad: Composed of two teams and is typically led by a Staff Sergeant. 9–10 soldiers.
- Team: The smallest unit. A fireteam consists of a team leader (usually a Sergeant, but may be as low as a PFC in rare cases), a rifleman, a grenadier, and an automatic rifleman. A sniper team consists of a sniper who takes the shot and a spotter who assists in targeting. 2–4 soldiers.
Army Commands 
The Army is currently undergoing a period of transformation, which is expected to be finished in 2013. When it is finished, there will be six geographical commands which will line up with the five geographical Unified Combatant Commands (COCOM).
- United States Army Central headquartered at Shaw Air Force Base, South Carolina
- United States Army North headquartered at Peterson Air Force Base, Colorado
- United States Army South headquartered at Fort Sam Houston, Texas
- United States Army Europe headquartered at Campbell Barracks, Heidelberg, Germany
- United States Army Africa headquartered at Caserma Ederle, Vicenza, Italy
- United States Army Pacific headquartered at Fort Shafter, Hawaii.
Each command will eventually have a numbered army as operational command, except in the case of U.S. Army Pacific, which will not maintain one but will have a numbered army for U.S. Army forces in the Republic of Korea.
Army groups 
Army groups were utilized during World War II only.
- First United States Army Group ('phantom' formation in World War II)
- Sixth United States Army Group
- Twelfth United States Army Group
- 15th Army Group
- I Corps headquartered at Fort Lewis, Washington
- II Corps
- III Corps headquartered at Fort Hood, Texas
- IV Corps
- V Corps, headquartered in Germany
- VI Corps
- VII Corps
- VIII Corps
- IX Corps
- X Corps
- XI Corps
- XII Corps
- XIII Corps
- XIV Corps
- XV Corps
- XVIII Airborne Corps headquartered at Fort Bragg, North Carolina
As the specialist page Divisions of the United States Army indicates, the US Army has had over 70 divisions in its twentieth century history. As an overview page, listing them all would distort the page. The compromise is to go "one back" and list the divisions as of peak strength during the Cold War, after the Reagan expansion had resulted in a force of 18 active and ten ARNG divisions.
Regular Army Divisions
- 1st Armored Division
- 2d Armored Division
- 3d Armored Division
- 1st Cavalry Division
- 1st Infantry Division
- 2d Infantry Division
- 3d Infantry Division
- 4th Infantry Division
- 5th Infantry Division
- 6th Infantry Division
- 7th Infantry Division
- 8th Infantry Division
- 9th Infantry Division
- 10th Mountain Division
- 24th Infantry Division
- 25th Infantry Division
- 82d Airborne Division
- 101st Airborne Division
- 26th Infantry Division
- 28th Infantry Division
- 29th Infantry Division
- 35th Infantry Division
- 38th Infantry Division
- 40th Armored Division
- 42d Infantry Division
- 47th Infantry Division
- 49th Armored Division
- 50th Armored Division
- 2nd Cavalry Regiment (Stryker brigade combat team) at Vilseck, Germany
- 3rd Armored Cavalry Regiment (ACR) at Fort Hood, Texas
- 11th Armored Cavalry Regiment (multi-compo heavy brigade combat team) at Fort Irwin, California
- 170th Infantry Brigade 170th Brigade Combat Team
- 172nd Infantry Brigade 172nd Brigade Combat Team
- 173rd Airborne Brigade Combat Team (infantry brigade combat team (airborne)) at Vicenza, Italy
Combat Brigades: 48
- 19 Heavy Brigade Combat Teams
- 6 Stryker Brigade Combat Teams
- 13 Infantry Brigade Combat Teams (light)
- 6 Infantry Brigade Combat Teams (airborne)
- 4 Infantry Brigade Combat Teams (air assault)
Smaller units 
Combat formations of the US Army at below brigade level include the United States Army Special Forces groups and several reserve separate battalions (100–442 Inf (USAR), 3-172 Inf (Mtn) (Vermont Army National Guard) etc.).
Arms and Services 
Category:Branches of the United States Army
Personnel in the Army work in various branches. This term refers to their area of training or expertise. See: United States Army branch insignia. (The term Branch of service also refers to the different United States armed forces.)
See also 
- See the Continental Staff System for an explanation of "letter-number" (e.g. G-8) designations.
- Perpich v. Department of Defense, 496 U.S. 334 (1990)
- Army Reserve Marks First 100 Years : Land Forces : Defense News Air Force
- US Third Army Website
- "SETAF Takes on a new mission" (Press release). United States Army. 10 Dec. 2008.
- "SETAF assumes new mission as Army AFRICOM component" (Press release). United States Army. 13 Jan. 2009.
- "U.S. Army Africa official mission statement". 2 Nov. 2009.
- Organization, United States Army
- www.usaraf.army.mil Major General David R. Hogg, Commander, U.S. Army Africa . Retrieved 26 June 2010.
- "US Army Pacific CG Bio". Retrieved 20 November 2011.
- "Commanding General". United States Army, Surface Deployment and Distribution Command. 30 June 2008. Retrieved 4 July 2008.[dead link]
- "Army Birthdays". United States Army Center of Military History. 31 July 2009. Retrieved 1 June 2010.