During WWII, its first assignment was to the British Expeditionary Force. Along with virtually the whole of that force, it was evacuated from Dunkirk after the Germans broke through Allied lines. I Corps then remained in the United Kingdom until the landings in Normandy for Operation Overlord. It was assigned to Second Army in 21st Army Group for most of the campaign in France, the Low Countries and Germany.
After the defeat of Germany, 21st Army Group became the British Army of the Rhine, and I Corps was transformed into a corps district, with an administrative, rather than combat, role. It was disbanded in 1947. However, in 1951 the Corps was reactivated to become the principal combat element of the BAOR. I Corps was redesignated Headquarters Allied Command Europe Rapid Reaction Corps with the end of the Cold War.
The structure of a corps is not permanent; many of the units that is commands are allocated to it as needed on an adhoc basis.
In the British Army, a corps tends to be a grouping by common function (eg, the Infantry corps, the Royal Logistics Corps[?], Royal Corps of Signals[?]).
There is a corps headquarters for operational control of forces, and it was last deployed as the headquarters commanding land forces during the Kosovo War in 1999.
On 9 January 1945, I U.S. Corps successfully landed on the coast of the Lingayen Gulf in Northern Luzon, P.I., with the mission of establishing a base for future operations to the north and of denying the enemy northern access to the China Sea.
The Corps had only a short period of inactivity, for with the entry of American troops into Korea it was again to be the "first"; I U.S. Corps was reactivated at Fort Bragg, North Carolina, on 2 August 1950 and advance elements of the headquarters took their place in the Pusan perimeter on 27 August.
Four days later the Corps participated in the attack that was to mark the changing tide of American fortunes; from the Pusan perimeter Corps troops pushed northward against crumbling enemy opposition to establish contact with forces of the 7th Infantry Division driving southward from the beachhead established by the amphibious landings at Inchon.