Twenty-first Army Group

21st Army Group
21st Army Group Shoulder Flash
Active	1943–45
Country	United Kingdom
Branch	British Army
Type	Army Group
Size	200,000
Part of	Allied Expeditionary Force
Commanders
Notable commanders	Bernard Paget Bernard Montgomery

The 21st Army Group was a World War II British headquarters formation, in command of two field armies and other supporting units, consisting primarily of the British Second Army and the First Canadian Army. Established in London during July 1943, under the command of Supreme Headquarters Allied Expeditionary Force (SHAEF), it was assigned to Operation Overlord, the Western Allied invasion of Europe, and was an important Allied force in the European Theatre. The 21st Army Group operated in Northern France, Luxembourg, Belgium, the Netherlands and Germany from June 1944 until the end of the war in Europe in May 1945, after which it was redesignated the British Army of the Rhine (BAOR).

Commanded by General (later Field Marshal) Sir Bernard Montgomery, 21st Army Group initially controlled all ground forces in Operation Overlord (the United States First Army and British Second Army). When sufficient American forces had landed, their own 12th Army Group was activated, under General Omar Bradley, and the 21st Army Group was left with the British Second Army and the newly activated First Canadian Army which, despite its title, also contained many British and Polish troops.