Editing Corps (section)

===== 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.<ref name="Eicher65">Eicher,&nbsp;J.,&nbsp;Eicher,&nbsp;D.&nbsp;(2002).&nbsp;Civil War High Commands.&nbsp;United States:&nbsp;Stanford University Press. pages 65-66</ref>  Major General [[George B. McClellan]], for example, planned to organize the [[Army of the Potomac]] into corps of two or more [[Divisions of the United States Army#American Civil War|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.<ref name="Wilson12">Wilson,&nbsp;J.&nbsp;B.&nbsp;(1998).&nbsp;Maneuver and Firepower: The Evolution of Divisions and Separate Brigades.&nbsp;United States:&nbsp;Center of Military History, U.S. Army. pages 12-15</ref>

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.<ref name="Eicher65"/><ref name="NCMuseum">{{cite web|title=Civil War Army Organization and Rank|url=https://www.ncmuseumofhistory.org/civil-war-army-organization-and-rank|publisher=North Carolina Museum of History|access-date=23 January 2022|archive-date=18 July 2017|archive-url=https://web.archive.org/web/20170718010330/http://ncmuseumofhistory.org/civil-war-army-organization-and-rank|url-status=dead}}</ref> 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 led to the creation of a dedicated [[Cavalry Corps (Union Army)|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 (United States Army)#American Civil War|brigade]] of between four and six [[artillery battery|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.<ref name="Wilson12"/><ref name="McGrath17">McGrath, John J. The Brigade: A History, Its Organization and Employment in the US Army.&nbsp;(2004).&nbsp;Fort Leavenworth, Kansas : Combat Studies Institute, US Army Command and General Staff College. pages 17-19</ref>

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).<ref name="McGrath17"/> To assist with their command, generals were allowed a number of [[Aide-de-camp|aides-de-camp]] and a [[military staff|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:<ref>Eicher, page 40</ref> 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 (United States)|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.<ref>Shrader,&nbsp;C.&nbsp;R.,&nbsp;Newell,&nbsp;C.&nbsp;R.&nbsp;(2011).&nbsp;Of Duty Well and Faithfully Done: A History of the Regular Army in the Civil War.&nbsp;United States:&nbsp;Nebraska. page 71</ref>

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.<ref name="Wilson12"/><ref name="McGrath17"/> 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]].{{citation needed|date=July 2014}}

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]] counterparts because their divisions contained more brigades, each of which could contain more regiments. All of the Confederate corps at the [[Battle of Gettysburg]], for instance, exceeded 20,000 men. However, for both armies, unit sizes varied dramatically with attrition throughout the war. In Civil War usages, by both sides, it was common to write out the number, thus "Twenty-first Army Corps", a practice that is usually ignored in modern histories of the war.