The British I Corps has a long history, and was in existence as an active formation in the British Army for longer than any other corps.
During WWI it was part of the original British Expeditionary Force, under the command of Sir Douglas Haig, and remained on the Western Front throughout the war.
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.
