A Corps ("core"; plural /ˈkɔərz/ spelled the same as singular; from French, from the Latin corpus "body") is either a large formation, or an administrative grouping of troops within an armed force with a common function such as Artillery or Signals representing an arm of service. Corps may also refer to a branch of service such as the United States Marine Corps, the Corps of Royal Marines, the Honourable Corps of Gentlemen at Arms, or the Corps of Commissionaires.
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 the US and in some European armed forces the number of a corps is traditionally indicated in Roman numerals (e.g. XXI Corps).
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.
It took command of the International Security Assistance Force in Afghanistan on 4th 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.
The pre-World War II Red Army of the former USSR had rifle corps much like in the Western sense with approximately three divisions to a corps. However, after the war started, the recently-purged Soviet senior command (Generals) structure was apparently unable to handle the formations, and the armies and corps were integrated into new, smaller "Armies" and those into fronts. Rifle Corps were re-established during the war after Red Army commanders had gained experience handling larger formations. Before and during World War II, however, Soviet armored units were organized into corps. The pre-war Mechanized Corps were made up of divisions. In the reorganizations, these "Corps" were reorganized into tank brigades and support units, which in terms of actual strength were equivalent to armored divisions in most other armies. Due to this, they are sometimes, informally, referred to as "Brigade Buckets".
After the war, the Tank and Mechanized Corps were re-rated as divisions. During the reforms of 1956-58, most of the corps were again disbanded to create the new Combined Arms and Tank Armies. A few corps were nevertheless retained, of both patterns. The Vyborg and Archangel Corps of the Leningrad Military District were smaller armies with three low-readiness motorized rifle divisions each. The Category A Unified Corps of the Belarussian Military District (Western TVD/Strategic Direction) and Carpathian Military District (also Western TVD) were of the brigade pattern.
The Soviet Air Force used ground terminology for its formations down to squadron level. As intermediates between the Division and the Air Army were Corps—these also had three Air Divisions each.
In Australia, soldiers belong foremost to a Corps which defines a common function or employment across the army. The Australian Army has a system of coloured lanyards, which each identify a soldier as part of a specific Corps (or sometimes individual battalion). This lanyard is a woven piece of cord which is worn on ceremonial uniforms and dates back to the issue of clasp knives in the early 20th century which were secured to the uniform by a length of cord. If a soldier is posted to a unit outside of their parent corps, except in some circumstances the soldier continues to wear the hat badge and lanyard of their Corps (e.g. a Clerk posted to an infantry battalion would wear the lanyard of the Royal Australian Ordnance Corps)
In Canada, with the integration of the Canadian army into the Canadian Forces, the British Corps model was replaced with personnel branches, defined in Canadian Forces Administrative Orders (CFAOs) as "...cohesive professional groups...based on similarity of military roles, customs and traditions." CFAO 2-10) However, the Armour Branch has continued to use the title Royal Canadian Armoured Corps, the Infantry Branch continued to use the Royal Canadian Infantry Corps designation, and the Artillery Branch uses the term Royal Regiment of Canadian Artillery.
The Corps system is also used in the U.S. Army to group personnel with a common function, but without a regimental system there is less variation in insignia and tradition. These are often referred to as "Branches" and include the Quartermaster Corps, Ordnance Corps, Transportation Corps, Medical Corps, Chaplain Corps, Judge Advocate General's Corps, & Finance Corps. Each of these Corps is also considered a "Regiment" for historic purposes but these Regiments have no tactical function.
In the US, there are non-military, administrative, training and certification Corps for commissioned officers of the government's uniformed services such as the Police Corps, the Public Health Service Commissioned Corps and the National Oceanic And Atmospheric Administration Corps