# XXI Corps (German Empire)

The XXI Army Corps / XXI AK (German: XXI. Armee-Korps) was a corps level command of the German Army, before and during World War I.
As the German Army expanded in the latter part of the 19th century and early part of the 20th century, the XXI Army Corps was set up on 1 October 1912 in Saarbrücken as the Generalkommando (headquarters) for the districts of Koblenz, Trier and part of Alsace-Lorraine. It took over command of 31st Division from XV Corps and the newly formed 42nd Division (the last division to be formed by the peacetime army). General der Infanterie Fritz von Below, former commander of 1st Guards Division, took command.
It was assigned to the VII Army Inspectorate. but joined the predominantly Bavarian 6th Army at the start of the First World War. It was still in existence at the end of the war in the 5th Army, Heeresgruppe Gallwitz on the Western Front.

## Peacetime organisation

The 25 peacetime Corps of the German Army (Guards, I - XXI, I - III Bavarian) had a reasonably standardised organisation. Each consisted of two divisions with usually two infantry brigades, one field artillery brigade and a cavalry brigade each. Each brigade normally consisted of two regiments of the appropriate type, so each Corps normally commanded 8 infantry, 4 field artillery and 4 cavalry regiments. There were exceptions to this rule:
    V, VI, VII, IX and XIV Corps each had a 5th infantry brigade (so 10 infantry regiments)
    II, XIII, XVIII and XXI had a 9th infantry regiment
    I, VI and XVI Corps had a 3rd cavalry brigade (so 6 cavalry regiments)
    the Guards Corps had 11 infantry regiments (in 5 brigades) and 8 cavalry regiments (in 4 brigades).
Each Corps also directly controlled a number of other units. This could include one or more
    Foot Artillery Regiment
    Jäger Battalion
    Pioneer Battalion
    Train Battalion
Peacetime organization of the Corps :
| Corps | Division | Brigade | Units | Garrison |
| XXI Corps | 31st Division | 32nd Infantry Brigade | 70th (8th Rhenish) Infantry | Saarbrücken |
| XXI Corps | 31st Division | 32nd Infantry Brigade | 174th (10th Lotharingian) Infantry | Forbach |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 60th (7th Brandenburg) Infantry "Margrave Charles" | Weißenburg |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 137th (2nd Lower Alsatian) Infantry | Hagenau |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 166th (Hessen-Homburg) Infantry | Bitsch |
| XXI Corps | 31st Division | 31st Field Artillery Brigade | 31st (1st Lower Alsatian) Field Artillery | Hagenau |
| XXI Corps | 31st Division | 31st Field Artillery Brigade | 67th (2nd Lower Alsatian) Field Artillery | Hagenau, Bischweiler |
| XXI Corps | 31st Division | 31st Cavalry Brigade | 7th (Westphalian) Dragoons | Saarbrücken |
| XXI Corps | 31st Division | 31st Cavalry Brigade | 7th (Rhenish) Uhlans "Archduke Frederick of Baden" | Saarbrücken |
| XXI Corps | 42nd Division | 59th Infantry Brigade | 97th (1st Upper Rhenish) Infantry | Saarburg |
| XXI Corps | 42nd Division | 59th Infantry Brigade | 138th (3rd Lower Alsatian) Infantry | Dieuze |
| XXI Corps | 42nd Division | 65th Infantry Brigade | 17th (4th Westphalian) Infantry "Count Barfuss" | Mörchingen |
| XXI Corps | 42nd Division | 65th Infantry Brigade | 131st (2nd Lotharingian) Infantry | Mörchingen |
| XXI Corps | 42nd Division | 42nd Field Artillery Brigade | 8th (1st Rhenish) Field Artillery "von Holtzendorff" | Saarbrücken |
| XXI Corps | 42nd Division | 42nd Field Artillery Brigade | 15th (1st Upper Alsatian) Field Artillery | Saarburg, Mörchingen |
| XXI Corps | 42nd Division | 42nd Cavalry Brigade | 11th (2nd Brandenburg) Uhlans "Count Haeseler" | Saarburg |
| XXI Corps | 42nd Division | 42nd Cavalry Brigade | 15th (Schleswig-Holstein) Uhlans | Saarburg |
| XXI Corps | Corps Troops | | 3rd Machine Gun Abteilung | Saarburg |
| XXI Corps | Corps Troops | | 27th (2nd Rhenish) Pioneer Battalion | Trier |
| XXI Corps | Corps Troops | | 21st (2nd Rhenish) Train Battalion | Forbach |
| XXI Corps | Saarbrücken Defence Command (Landwehr-Inspektion) | | | Saarbrücken |

## World War I
### Organisation on mobilisation

On mobilization on 2 August 1914 the Corps was restructured. 42nd Cavalry Brigade was withdrawn to form part of the 7th Cavalry Division and the 31st Cavalry Brigade was broken up and its regiments assigned to the divisions as reconnaissance units. Divisions received engineer companies and other support units from the Corps headquarters. Unusually, the Corps retained its 9th infantry regiment on mobilisation. In summary, XXI Corps mobilised with 27 infantry battalions, 9 machine gun companies (54 machine guns), 8 cavalry squadrons, 24 field artillery batteries (144 guns), 4 heavy artillery batteries (16 guns), 3 pioneer companies, and an aviation detachment.
Initial wartime organization of the Corps :
| Corps | Division | Brigade | Units |
| XXI Corps | 31st Division | 32nd Infantry Brigade | 70th Infantry Regiment |
| XXI Corps | 31st Division | 32nd Infantry Brigade | 174th Infantry Regiment |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 60th Infantry Regiment |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 137th Infantry Regiment |
| XXI Corps | 31st Division | 62nd Infantry Brigade | 166th Infantry Regiment |
| XXI Corps | 31st Division | 31st Field Artillery Brigade | 31st Field Artillery Regiment |
| XXI Corps | 31st Division | 31st Field Artillery Brigade | 67th Field Artillery Regiment |
| XXI Corps | 31st Division | | 7th Uhlan Regiment |
| XXI Corps | 31st Division | | 1st Company, 27th Pioneer Battalion |
| XXI Corps | 31st Division | | 31st Divisional Pontoon Train |
| XXI Corps | 31st Division | | 1st Medical Company |
| XXI Corps | 42nd Division | 59th Infantry Brigade | 97th Infantry Regiment |
| XXI Corps | 42nd Division | 59th Infantry Brigade | 138th Infantry Regiment |
| XXI Corps | 42nd Division | 65th Infantry Brigade | 17th Infantry Regiment |
| XXI Corps | 42nd Division | 65th Infantry Brigade | 131st Infantry Regiment |
| XXI Corps | 42nd Division | 42nd Field Artillery Brigade | 8th Field Artillery Regiment |
| XXI Corps | 42nd Division | 42nd Field Artillery Brigade | 15th Field Artillery Regiment |
| XXI Corps | 42nd Division | | 7th Dragoon Regiment |
| XXI Corps | 42nd Division | | 2nd Company, 27th Pioneer Battalion |
| XXI Corps | 42nd Division | | 3rd Company, 27th Pioneer Battalion |
| XXI Corps | 42nd Division | | 42nd Divisional Pontoon Train |
| XXI Corps | 42nd Division | | 2nd Medical Company |
| XXI Corps | 42nd Division | | 3rd Medical Company |
| XXI Corps | Corps Troops | | II Battalion, 3rd Foot Artillery Regiment |
| XXI Corps | Corps Troops | | 8th Aviation Detachment |
| XXI Corps | Corps Troops | | 21st Corps Pontoon Train |
| XXI Corps | Corps Troops | | 21st Telephone Detachment |
| XXI Corps | Corps Troops | | 27th Pioneer Searchlight Section |
| XXI Corps | Corps Troops | | Munition Trains and Columns corresponding to II Corps |

### Combat chronicle

On mobilisation, XXI Corps was assigned to the predominantly Bavarian 6th Army forming part of the left wing of the forces for the Schlieffen Plan offensive in August 1914 on the Western Front. By 1915 it was on the Eastern Front where it took part in the siege of Kovno and the battles on the Neman River and at Vilnius. It was still in existence at the end of the war in the 5th Army, Heeresgruppe Gallwitz on the Western Front.

## Commanders

The XXI Corps had the following commanders during its existence:
| Dates | Rank | Name |
| 1 October 1912 to 4 April 1915 | General der Infanterie | Fritz von Below |
| 4 April 1915 to 2 January 1917 | Generalleutnant | Oskar von Hutier |
| 2 January 1917 to end of war | Generalleutnant | Ernst von Oven |