corps

Corps (; plural ''corps'' ; from French , from the Latin "body") is a term used for several different kinds of organization. A military innovation by Napoleon I, the formation was first named as such in 1805. The size of a corps varies greatly, but from two to five divisions and anywhere from 40,000 to 80,000 are the numbers stated by the US Department of Defense.

Within military terminology a corps may be:
*an operational formation, sometimes known as a field corps, which consists of two or more divisions, such as the , later known as ("First Corps") of Napoleon I's );
*an administrative corps (or mustering) – that is a specialized branch of a military service (such as an artillery corps, a medical corps, or a force of military police) or;
*in some cases, a distinct service within a national military (such as the United States Marine Corps).
These usages often overlap.

Corps may also be a generic term for a non-military organization, such as the US Peace Corps and European Solidarity Corps.

Military usage

Operational formation

In many armies, a corps is a battlefield formation composed of two or more divisions, and typically commanded by a lieutenant general. During World War I and World War II, due to the large scale of combat, multiple corps were combined into armies which then formed into army groups. In Western armies with numbered corps, the number is often indicated in Roman numerals (e.g., VII Corps).

Australia

The Australian and New Zealand Army Corps was raised in 1914, consisting of Australian and New Zealand troops, who went on to fight at Gallipoli in 1915. In early 1916, the original corps was reorganized and two corps were raised: I ANZAC Corps and II ANZAC Corps. In the later stages of World War I, the five infantry divisions of the First Australian Imperial Force (AIF)—consisting entirely of personnel who had volunteered for service overseas—were united as the Australian Corps, on the Western Front, under Lieutenant General Sir John Monash.

During World War II, the Australian I Corps was formed to co-ordinate three Second Australian Imperial Force (2nd AIF) units: the 6th, 7th and 9th Divisions, as well as other Allied units on some occasions, in the North African campaign and Greek campaign. Following the commencement of the Pacific War, there was a phased withdrawal of I Corps to Australia, and the transfer of its headquarters to the Brisbane area, to control Allied army units in Queensland and northern New South Wales (NSW). II Corps was also formed, with Militia units, to defend south-eastern Australia, and III Corps controlled land forces in Western Australia. Sub-corps formations controlled Allied land forces in the remainder of Australia. I Corps headquarters was later assigned control of the New Guinea campaign. In early 1945, when I Corps was assigned the task of re-taking Borneo, II Corps took over in New Guinea.

Canada

Canada first fielded a corps-sized formation in the First World War; the Canadian Corps was unique in that its composition did not change from inception to the war's end, in contrast to British corps in France and Flanders. The Canadian Corps consisted of four Canadian divisions. After the Armistice, the peacetime Canadian militia was nominally organized into corps and divisions but no full-time formations larger than a battalion were ever trained or exercised. Early in the Second World War, Canada's contribution to the British-French forces fighting the Germans was limited to a single division. After the fall of France in June 1940, a second division moved to England, coming under command of a Canadian corps headquarters. This corps was renamed I Canadian Corps as a second corps headquarters was established in the UK, with the eventual formation of five Canadian divisions in England. I Canadian Corps eventually fought in Italy, II Canadian Corps in northwest Europe, and the two were reunited in early 1945. After the formations were disbanded after VE Day, Canada has never subsequently organized a corps headquarters.

Royal Canadian Army Cadets: A corps size in the RCAC is different everywhere, depending on the size. The commanding officer can be a captain or major.

China

The National Revolutionary Army (NRA) corps () was a type of military organization used by the Chinese Republic, and usually exercised command over two to three NRA divisions and often a number of independent brigades or regiments and supporting units. The Chinese Republic had 133 corps during the Second Sino-Japanese War. After losses in the early part of the war, under the 1938 reforms, the remaining scarce artillery and the other support formations were withdrawn from the division and was held at corps, or army level or higher. The corps became the basic tactical unit of the NRA having strength nearly equivalent to an allied division.

The modern People's Liberation Army Ground Force group army () is the closest equivalent of a corps. After the military reforms of the early 2010s, a typical PLA group army consists of six infantry and armoured brigades, plus additional artillery, air defence and army aviation assets. Each formation contains approximately 30,000 combat troops and several thousands more supporting personnel.

France

The French Army under Napoleon I used corps-sized formations (french: corps d'armée) as the first formal combined-arms groupings of divisions with reasonably stable manning and equipment establishments. Napoleon I first used the in 1805. The use of the was a military innovation that provided Napoleon I with a significant battlefield advantage in the early phases of the Napoleonic Wars. The corps was designed to be an independent military group containing cavalry, artillery and infantry, and capable of defending against a numerically superior foe. This allowed Napoleon I to mass the bulk of his forces to effect a penetration into a weak section of enemy lines without risking his own communications or flank. This innovation stimulated other European powers to adopt similar military structures. The corps has remained an echelon of French Army organization to the modern day.

Germany

As fixed military formation already in peace-time it was used almost in all European armies after Battle of Ulm in 1805. In Prussia it was introduced by ''Order of His Majesty'' (german: Allerhöchste Kabinetts-Order) from 5 November 1816, in order to strengthen the readiness to war.

India

The Indian Army has 14 corps, each commanded by a general officer commanding (GOC), known as the corps commander, who holds the rank of lieutenant general. Each corps is composed of three or four divisions. There are three types of corps in the Indian Army: strike, holding and mixed. The corps HQ is the highest field formation in the army.

Pakistan

The Pakistan Army has nine manoeuvre corps, each commanded by a lieutenant general. Each corps is composed of at least two divisions. The corps HQ is the highest field formation in the army.

The paramilitary forces of Pakistan's two western provinces of Khyber Pakhtunkhwa and Balochistan are the Frontier Corps (FC), which were founded in 1907 during British rule. They are charged with guarding the country's western borders as well as providing internal security including guarding important sites and participating in law enforcement. They are divided into four sub-organisations: FC Khyber Pakhtunkhwa (North), FC Khyber Pakhtunkhwa (South), FC Balochistan (North), and FC Balochistan (South).

Poland (1938–1939)

The Polish Armed Forces used independent operational groups in the place of the corps before and during World War II. An example would be Independent Operational Group Polesie. The groups, as the name indicates, were more flexible and showed greater capacity to absorb and integrate elements of broken units over a period of just a couple days and keep cohesion during the September Campaign than more traditional army units such as divisions, regiments, or even brigades.

United Kingdom

Wellington formed a in 1815 for commanding his mixed allied force of four divisions against Napoleon I.

When the British Army was expanded from an expeditionary force in the First World War, corps were created to manage the large numbers of divisions. The British corps in World War I included 23 infantry corps and a few mounted corps. The word was adopted for other special formations such as the Officers Training Corps. Military training of teenage boys is undertaken at secondary schools through the Combined Cadet Force, in which participation was compulsory at some schools in the 1950s. Schoolboy jargon called the CCF simply "Corps".

The British Army still has a corps headquarters for operational control of forces. I Corps of the British Army of the Rhine was redesignated the Allied Rapid Reaction Corps in 1994. It is no longer a purely British formation, although the UK is the "framework nation" and provides most of the staff for the headquarters. A purely national Corps headquarters could be quickly reconstituted if necessary.

It took command of the International Security Assistance Force in Afghanistan on 4 May 2006. Previously, it was deployed as the headquarters commanding land forces during the Kosovo War in 1999 and also saw service in Bosnia and Herzegovina, commanding the initial stages of the IFOR deployment prior to that in 1996. Otherwise, the only time a British corps headquarters has been operationally deployed since 1945 was II Corps during the Suez Crisis.

United States

The structure of a field corps in the United States Army is not permanent; many of the units that it commands are allocated to it as needed on an ''ad hoc'' basis. On the battlefield, the corps is the highest level of the forces that is concerned with actual combat and operational deployment. Higher levels of command are concerned with administration rather than operations, at least under current doctrine. The corps provides operational direction for the forces under its command.

As of 2014, the active field corps in the US Army are I Corps ("eye core"), III Corps and XVIII Airborne Corps; their lineages derive from three of the corps formed during World War I (I and III Corps) and World War II (XVIII Airborne Corps). On 12 February 2020, it was announced that the Army was reactivating V Corps to bolster the presence of US forces in Europe.

= American Civil War

=
The first field corps in the United States Army were legalized during the American Civil War by an act of Congress on 17 July 1862, although the term had been used previously to refer to any large portion of the army.Eicher, J., Eicher, D. (2002). Civil War High Commands. United States: Stanford University Press. pages 65-66 Major General George B. McClellan, for example, planned to organized the Army of the Potomac into corps of two or more divisions and about 25,000 soldiers. However he delayed doing so partly for lack of experienced officers and partly for political reasons, until March 1862 when President Lincoln ordered their creation.Wilson, J. B. (1998). Maneuver and Firepower: The Evolution of Divisions and Separate Brigades. United States: Center of Military History, U.S. Army. pages 12-15

The exact composition of a corps in the Union Army varied during the war, though it usually consisted of between two and six division (on average three) for approximately 36,000 soldiers. After Ambrose Burnside was given command of the Army of the Potomac in November 1862, he reorganized it into three "grand divisions" of two corps and a cavalry division each, but this structure was abolished when Joseph Hooker took over February 1863. This also lead to the creation of a dedicated Cavalry Corps of three divisions and horse artillery assigned to the corps headquarters. In the early years of the war, field artillery was either part of an artillery reserve under direct army control or assigned to individual divisions. However, after the Battle of Chancellorsville the divisional artillery was placed under corps control, with each corps assigned a brigade of between four and six batteries commanded by the senior-most artillery officer. In general the other field armies tended to model their organization after the Army of the Potomac, including the gradual development of corps.McGrath, John J. The Brigade: A History, Its Organization and Employment in the US Army. (2004). Fort Leavenworth, Kansas : Combat Studies Institute, US Army Command and General Staff College. pages 17-19

Corps were commanded by major generals because Congress refused to promote officers past that grade (with the exception of Ulysses S. Grant to lieutenant general in 1864). To assist with their command, generals were allowed a number of aides-de-camp and a general staff of other officers. This staff consisted of a chief of cavalry, a chief of artillery, and representatives of the War Department's various bureaus: an assistant adjutant general, a quartermaster, an assistant inspector general, a commissary of subsistence, an ordnance officer (all with the rank of lieutenant colonel) and a medical director. However, there were no dedicated combat service support formations as part of the corps. This meant that either civilian workers had to be hired or line soldiers detailed from their units to carry out the necessary tasks.

Initially, corps were numbered in relation to their field army, such as I Army Corps, Army of the Potomac. After a while these numerical designations became unique to each corps regardless of the army to which they were assigned. Although designated with numbers that are sometimes the same as those found in the modern US Army, there is no direct lineage between the 43 Union field corps of the Civil War and those with similar names in the modern era, due to congressional legislation caused by the outcry from veterans of the Grand Army of the Republic during the Spanish–American War.

In the Confederate States Army, field corps were authorized in November 1862. They were commanded by lieutenant generals, and were usually larger than their Union Army