The Higher Commands on the Western Front can be found HERE

The evolution of the higher commands on the Eastern front were more complicated as it included mixed commands with Germany's Allies.

At the start of the war the main force was the 8. Armee with the Landwehrkorps, which although attached to the 8. A.O.K. served far away on the left wing of the 1st Austro-Hungarian army.
The 9. Armee was formed in Breslau and Hindenburg took command of this after having led the 8. Armee to victory at Tannenburg and at the Masurischen lakes. The two armies were joined by ragtag Grenzschutz units under the command of the governors of the fortresses and the Stellvertretender Kommandierenden Generalen of the border areas.

In November 1918 the 8. amd 9. Armeen were united under Hindenburg who was named Oberbehehlshaber Ost. General der Kavallerie von Mackensen took over the 9. Armee.

The Oberbehehlshaber Ost needed permission to engage in major offensive operations and was initially to remain of the defensive. Hindenburg formed the Armeegruppe Graudenz out of Grenzschutz, Festungs and Ersatz troops to protect his left flank and renamed the Landwehrkorps Armee-Abteilung Woyrsch, using it to defend his right flank. The Armeegruppe Graudenz was renamed Armeegruppe Gallwitz in Febuary 1915 and the Armee-Abteilung Woyrsch became the Armee Woyrsch when it became under Austro Hungarian command in November 1914.

Left: General von Mackensen

The serious situation in the Carpathians in January 1915 led to the formation of a Südarmee which fell under Austro Hungarian command. At the same time the 10. A.O.K. was formed and fell under the command of the Oberbehehlshaber Ost in East Prussia.

At the beginning of February 1915 the forces were arranged as follows.
Under the Oberbehehlshaber Ost : The 8., 9., and 10. Armeen and Armeegruppe Gallwitz.
Under K.u.K. command: Armee Woyrsch, Austro-Hungarian 1., 4., 3., and 2. Armee, Süd-Armee, Austro-Hungarian Armee Gruppe Pflanzer-Baltin.

During the spring offensive in 1915 the Oberbehehlshaber Ost formed the Armee-Abteilung Lauenstein which marched into Kurland in April 1915. The 11. Armee had been formed for service in Galizien but in April 1915 it was in the line between the Austro-Hungarian 4. and 3. Armeen. The A.O.K. 11 took over the command of the Austro-Hungarian 4. Armee and was named Heeresgruppe Mackensen.

To the North the Armee-Abteilung Lauenstein was meeting superior enemy forces and the Oberbehehlshaber Ost sent the A.O.K.8 north to aid them. The Armee-Abteilung Lauenstein with reinforcements was renamed the Njemen-Armee, the name was taken over by the A.O.K. 8. To complicate matters the 8. Armee itself, detached from its A.O.K. was babysitted by the XX. A.K.

To the South Mackensen formed a Bug-Armee to serve alongside his 11. Armee.

In July 1915 the forces were arranged as follows

Under the Oberbehehlshaber Ost : The Njemen-Armee, 8., 9., and 10. Armeen and Armeegruppe Gallwitz.
Under K.u.K. command: Armee Woyrsch, Heeresgruppe Mackensen (11. Armee, Bug-Armee, Austro-Hungarian 4. and 1. Armee) Süd-Armee, Austro-Hungarian 7. and 2. Armee

Photo Right: General von Woyrsch

A major change occurred in August 1915. The Oberste Heeresleitung decided to take operational control of the Eastern Front, the Oberbehehlshaber Ost himself took over a Heeresgruppe. The 9. Armee joined the Armee-Abteilung Woyrsch which was no longer under Austro-Hungarian command. The Armee-gruppe Gallwitz became the 12. Armee. At the end of August the Heeresgruppe Mackensen along with the 11. Armee and Bug-Armee also left the Austro-Hungarian Command.

September 1915 saw the following constellation:
Heeresgruppe Hindenburg: Njemen Armee, 10., 8., and 12. Armee
Heeresgruppe Prinz Leopold von Bayern: 9. Armee and Armee-Abteilung Woyrsch
Heeresgruppe Mackensen: 11. and Bug-Armee.
Austro Hungarian high command with Austro Hungarian 4, 1, 2, 7 Armee and Süd Armee

Soon there were new changes, after the offensive on the 29th September 1915 the 8. Armee was disolved, the Southern Flank of the Njemen Armee became the Armee Abteilung Scholtz on the 28th october 1915 and the Njemen Armee was renamed as a new 8. Armee on the 30th December 1915.
Generalfeldmarchall Mackensen left on the 19th September to lead the offensive in Serbia after the 11. Armee had been dissolved 10 days before. The units of the 11. Armee came under the command of the former A.O.K.12 which was now renamed A.O.K. 11. At the same time A.O.K. 1 arrived from the western front and was renamed A.O.K.12. To replace the Heeresgruppe Mackensen the Heeresgruppe Linsingen was formed (with A.O.K. Bug)

The forces on the eastern front on the 1st January 1916 were as follows
Heeresgruppe Hindenburg: with 8. Armee, Armee Abteilung Scholtz, 10. and 12. Armee.
Heeresgruppe Linsingen:  Bug Armee and Austro Hungarian 4. Armee
Austro Hungarian Command: with 1.,2., and 7. Armee as well as the Sued Armee.

Left: Gen von Linsingen

This constellation remained for a relatively long time, it withstood the Russian attacks in March 1916, but the Russian June offensive led to changes on the Eastern front. Ludendorff wrote “During the difficult and tense days we spent in Kowno at the beginning of June we were in constant communication with the OHL. Time after time we stressed the need for a unified high command on the Eastern Front and at the end of June the Field Marshall and I were called to Pless to give our views on the situation on the Eastern Front...The journey changed little, there was still much resistance to a unified command....On the 27th July we made the journey again. The dangerous situation at Brody helped change the minds of our K.u.K. comrades and they approved Hindenburg taking over as supreme commander to the South of Brody.”
So from the 30th July 1916 the troops in the German sector of the Eastern front were once again under the command of the Oberbefehlshaber Ost whose area of command stretched from the northern oceans to the area west of Brody. This sector was known as the Heeresfront Hindenburg, the sector to the South Heeresfront Erzherzog Carl. The command of the Heeresgruppe Hindenburg passed to the A.O.K. 10 and was renamed Heeresgruppe Eichhorn. When Hindenburg changed yet again to become the Chef des Generalstabes des Feldheeres on the 29th August 1916 and Prinz Leopold von Bayern took over as Oberbefehlhaber Ost. The Heeresgruppe Leopold became the Heeresgruppe Woyrsch, loosing the 9. Armee which left to fight against the Romanians in Hungary. Because of the Romanian threat the Heeresgruppe Mackensen was formed in Northern Bulgaria on the 28th August.
After all these changes the front on the 19th September 1916 was as follows

Heeresfront des Oberbefehlshaber Ost
Heeresgruppe Eichhorn with 8. and 10. Armee and Armee Abteilung Scholtz.
Heeresgruppe Woyrsch with 12. Armee, A.Abt. Woyrsch, A.Abt. Gronau.
Heeresgruppe Linsingen with Bug Armee, Austro Hungarian 4. and 2.Armee (with Armee Gruppe Eben)

Neuer Absatz

Heeresfront Erzherzog Carl.
Süd Armee, Austro Hungarian 3., 7., and 1. Armee. 9. Armee
Heeresgruppe Mackensen with the Donau Armee and 3. Bulgarian Army.

By the 4th October 1916 the more changes had followed. The German Heeresfront had grown to include the Carpathian mountains. The Austro Hungarian Heeresgruppe Boehm Ermoli was formed with the Austro Hungarian 2. and 3. Armee and the Suedarmee. The Heeresgruppe came under the command of the Oberbefehlshaber Ost.
The 12. Armee was disbanded and replaced on the 10th October 1916 by the Armee Abteilung Scheffer. After Erzherzog Karl asended the throne his Heeresfront was taken over by Erzherzog Joseph on the 25th November 1916. The 9. Armee transfered to the HeeresgruppeMackensen on the 1st December 1916 and the Donau Armee came under the command of the 9. Armee on the 5th January 1917 after being renamed Generalkommando z.b.V. 52.

At this stage the front was as follows
Heeresfront des Oberbefehlshaber Ost - Heeresgruppe Eichhorn 8. and 10. Armee, Armee Abteilung D (Known as the A.Abt Scholtz until the 9th January 1917)
Heeresgruppe Linsingen - Bug Armee and Austro Hungarian 4. Armee
Austro Hungarian Heeresgruppe Boehm Ermolli with the Austro Hungarian 2. and 3. Armee and Sued Armee.
Heeresfront Erzherzog Joseph-Austro Hungarian 1. and 7. Armee, Heeresgruppe Mackensen with the 9. Armee and 3. Bulgarian Armee.

This constellation was to remain largely untouched for quite some time, in July 1917 the Austro Hungarian 3. Armee on the German right flank transferred to the Austrian Heeresfront. On the 15th December 1917 the Heeresgruppe Woyrsch was dissolved due to the ceasefire on the Eastern Front.
After the ceasefire, and especially after the peace of Brest Litowsk changes again changes occurred on the eastern front again. The Heeresgruppen Kommando Boehm Ermolli and the German Südarmee were dissolved on the 3rd of February 1918. With the exception of the Austro Hungarian 2.Armee the complete Heeresfront Erzherzog Joseph along with all Austro Hungarian Armies disappeared, the A.H. 2. Armee was renamed the A.H. Ostarmee. On the 28th of March 1918 the Heeresgruppe Eichhorn was dissolved. Eichhorn took command of the Heeresgruppe Linsingen on the 3rd April 1918.
The simplified Eastern Front on the 16th April 1918 was as follows
Oberbefehlshaber Ost with 8. and 10. Armee, Heeresgruppe Eichhorn-Kiew (After 1st May Eichhorn, after 13th August Kiew)

Austro Hungarian Ost Armee
Heeresgruppe Mackensen with 9. Armee and 3rd Bulgarian Armee.
After the peace with Romania on the 1st of July 1918 the Heeresgruppe Mackensen became the Besatzungsheer Rumaenien (Occupation Army Romania). The A.O.K. 9 had already left for the western front on the 18th June 1918. The Bulgarian 3rd Armee fell away on the 30th September 1918.
The expedition to free Finland on the 3rd April-29th July 1918 (Ostsee-Division) was not under Eastern front command but directly under the OHL.

To return to the chapter on hif´gher commands click HERE