Here's an article detailing the German replacement system during the war.
The German Replacement Army 1939 to 1945
by John Mulholland
During the course of the Second World War the Replacement and Training Divisions (Ersatzdivisionen), of the Third Reich, proved to be the lubricant that oiled the formidable German military machine.
Formed in the various German military districts (Wehrkreise), these divisions were tasked, after 27 August 1939, with “conscription, training and replacement of personnel including control of mobilization policies and the actual call-up and induction of men; all types of military training, including the selection and schooling of officers and non-commissioned officers; the dispatch of personnel replacements to field units in response to their requisitions; and the organization of new units.” (1)
Under control of the Replacement Army (Ersatzheer) (2), these Replacement and Training Divisions rose in strength from a total of 996,000 men at the start of WWII to a peak of 2,572,000 in December 1944. (3)
After the mobilization order was given by the Armed Forces High Command (Oberkommando der Wehrmacht) (4) each Wehrkreis of the Replacement Army began forming Replacement and Training Divisions as set down by order of the Chief of Army Equipment and Commander of the Replacement Army (Chef Heeresrüstung und Befehlshaber der Ersatzheer).
“The normal location of the Replacement (Ersatz) unit was the home station of the affiliated field unit, to which the soldiers expected ultimately to return for their discharge or for reassignment. For example, a soldier who was wounded and went to a reserve hospital in the Zone of the Interior (i.e. Germany) would be sent, upon leaving the hospital, to his affiliated Ersatz unit before being returned to the field.” (5)
“In order to understand the intricacies of the Ersatz system it is well to trace the successive stages of its development. Originally, each infantry regiment which took to the field at the beginning of the war left behind at its home station a battalion cadre bearing its own number and known as its Ersatz battalion. The primary purpose of this battalion was to receive recruits, train them, and dispatch them as replacements to the field regiments. At any given time it included reception (cadre) companies, training companies, convalescent companies and transfer companies. Typically the trained inductees combined with the convalescents into transfer companies for movement to a field unit. ………. The regimental staff also controlled from three to five infantry specialist replacement training companies which provided the personnel for the infantry howitzer companies, antitank companies, signal sub-units, engineer platoons, and mounted platoons or the three infantry field regiments.” (6)
“The number of replacement division staffs in each Wehrkreis was regulated by the Army High Command (Oberkommando des Heeres). They were responsible for the uniformity of training in their subordinate replacement training units and were to be kept free from all administrative duties.” (7)
From 01 September 1939 through to October 1942 the Replacement Army (also, sometimes, referred to as the Home Army) kept up a steady flow of new divisions and their trained replacement personnel to the far flung battlefields of Europe, Africa, and almost to the very gates of the Russian capital city of Moscow.
“The most far reaching change in the organization of the Replacement Army took place in October 1942 when all basic replacement training units were broken up into their two elements – one to handle induction and replacement and the other to handle training. The induction and replacement unit retained the designation Ersatz, but henceforth it was concerned only with receipt of recruits ……….forwarding of recruits as speedily as possible to the sister training unit; receipt of convalescents and sending them back to a field unit; ……….The newly created training units [Reservedivisionen] bore the same number as and received the men from the Ersatz unit, gave them their training, and then dispatched them to an affiliated field unit.” (8)
“Training in ersatz companies was abbreviated both for new recruits and for men released from hospitals. Both received from three to eight weeks basic training, depending on the judgment of the company officers as to when the men were ready. After the men finished basic training, small percentages, usually those destined for the Russian front, were sent to Ausbildung companies for advanced training.” (9)
“Divisions had a Feldersatz-Bataillon (field replacement battalion) to provide final training for new replacements. Occasionally local short-term training was undertaken by the armies, although for major training/schooling, personnel (and units) were transferred to the Ersatzheer. Feldheer units, when within "Greater Germany" were stationed with the Wehrkreis, and attached for administration (rations, accommodation, etc), but not for command purposes.” (10)
“In addition to the regular mobile infantry division and the static division, a third class existed in 1943, the reserve division. To make more manpower available for the divisions in Russia, reserve divisions were formed from the training battalions in Germany and assigned to occupation duties in France and Russia. Twelve such reserve divisions were sent to France in 1943 to replace infantry divisions sent to the East.
The creation of the reserve divisions hampered the training of new men to a certain degree. If a new draftee were not selected to go into the air force or the panzer force, he received up to four months of basic individual infantry training in a replacement and training battalion located in a barracks near his home in Germany. He was then sent either to a reserve division in the occupied territories or to a training unit behind the lines in Russia, where he received another four months of training while performing occupation duties or fighting partisans. Finally, he was assigned to a division where he was taught more skills in the replacement battalion.” (11)
“The Replacement Army constituted a major portion of the armed forces. Its operations played a major role in bolstering the perseverance of the Field Army. Throughout most of the war, for every two or three field army soldiers there was a replacement army soldier readying to move to the front. The system functioned surprisingly well.” The Wehrkreis was also responsible for rebuilding and refitting shattered divisions, a responsibility that also took on more importance as the war continued. “It rapidly filled the gaps of Stalingrad and Africa in early 1943. In the summer of 1944 it even managed to plug the gaping holes left by an army group [Heeresgruppe Mitte] in central Russia and part of another [Heeresgruppe Sudukraine] in Rumania.” (12)
Sources quoted above:
(1) Page 50: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(2) Note: Quoted from personal correspondence from Dr.Leo (W.G.) Niehorster to this writer:
“The Ersatzheer had under it the Military Districts (Wehrkreise) and all schools, institutes, training grounds, etc. and was responsible for raising all new Army units as well as training and initially equipping them.
(3) Page 55: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(4) Note: Quoted from personal correspondence from Dr. Leo (W.G.) Niehorster to this writer:
“The OKW was supposed to be a coordinator between/over the three services. It never really was. In any event, it had never at any time had anything to do with the administration/housekeeping of the army. The most it ever had regarding the Army (and Navy and Airforce) was operational control of units in the field. Nothing else. Ever.”
(5) Page 58: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(6) Page 59: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(7) Page 59: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(8) Page 61: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej
(9) Page 148: “Second Front NOW – 1943” by Dr. Walter S.Dunn, Jr
(10) Quoted from personal correspondence from Dr. Leo (W.G.) Niehorster and this writer.
(11) Pages 149-150: “Second Front NOW – 1943” by Dr.Walter S.Dunn, Jr
(12) Page 68: “German Army Order of Battle 1939 – 1945”, Volume I. by W.Victor Madej