Eingreif division

Eingreif division was a type of German Army formation of World War I established in 1917, which was responsible for engaging in immediate counter-attacks against enemy troops who broke through a defensive position being held by a "front-holding" division (Stellungsdivision).

Definition
Eingreif generally translated as counter-attack, but this does not capture the entire sense of the term. In German military doctrine it includes a sense of intervening decisively and is better understood as meaning interlocking. The term was adopted during the Battle of Arras (1917) as a replacement of an earlier term Ablösungsdivision ("relief division") to end confusion over the purpose of divisions held in reserve.

During the First World War, the German army differentiated clearly between an organised counter-attack (Gegenangriff) and a hasty counter-attack (Gegenstoss). The difference was largely to do with timings. A Gegenangriff implied a formal, deliberate attack with full preparatory artillery fire. A Gegenstoss was a hasty or immediate counter-thrust made to prevent the enemy from consolidating captured positions. The principal task of an Eingreif division was to conduct the more immediate Gegenstoss engagements, if troops held in reserve by the Stellungsdivision were insufficient to restore the position. To counteract the effect of an enemy penetration, these divisions were placed in readiness behind the trench system. The formation would have launched necessary manoeuvres in addition to the defensive efforts by the formation in situ.

Evolution
German defensive practices had been based on the publication "Drill Regulations for the Infantry, German Army, 1906" (Exerzier-Reglement für die infanterie). After the experience of the 1916 Battle of the Somme, General Erich Ludendorff had German defensive doctrine revised. On 1 December 1916, The Supreme Army Command published new tactical instructions in Principles of Command in the Defensive Battle in Position Warfare (Grundsätze für die Führung in der Abwehrschlacht im Stellungskrieg) and issued it to all divisions. On 30 January 1917, Ludendorff also circulated Experience of the German First Army in the Somme Battles (Erfahrungen der I Armee in der Sommeschlacht) by Colonel Fritz von Lossberg which contradicted the idea that troops in forward positions should be allowed to withdraw.. The result was that German commanders had two examples to consider when arranging their defences.

During the course of the Third Battle of Ypres, Lossberg's combination of forward defence and counter-attack from behind the front line was replaced by an elastic defence on Ludendorff's orders in October 1917. The new thinking emphasised the defensive battle as a fight in defensive zones for the front line rather than in the front line, to defeat the attack or to gain time for a counter-thrust by forces held in local reserve. In a rear battle zone specially trained Eingreif divisions, would be held back, ready to intervene with countering manoeuvres in support of the front zone garrisons. New deeper defensive positions composed of three defensive zones ("outpost", "battle" and "rear") which had been built according to the new manual Allgemeines über Stellenbau (Principles of Field Construction) and held by garrison or "trench" divisions (Stellungsdivisionen) in a defensive battle (Abwehrschlacht).

As the German army in the west was forced to make greater efforts in defence against Allied attacks in 1915–1917, counter-attacks became more sophisticated. Gegenstoss in der Stellung became counter-thrusts by local trench garrisons, while larger efforts by local reserves became Gegenstoss aus der Tiefe (counter-thrust from behind the position). As these practices developed, the role of the Eingreif division was to execute an instant and immediate counter-thrust (den sofortigen Gegenstoss) by moving to the front in stages to participate in a series of counter-thrusts.

Application
The leading regiment of an Eingreif division was to advance into the zone of the front division with its other two regiments moving forward in close support. The support and reserve assembly areas in the Flandern Stellung were termed Fredericus Rex Raum and Triarier Raum by analogy with the formation of a Roman legion (hastati, principes and triarii). Eingreif Divisions were accommodated 10000 - 12000 yd behind the front line and began their advance to their assembly areas in the rear zone (rückwärtige Kampffeld), ready to intervene in the main battle zone (Grosskampffeld).