Battle of Gumbinnen

Background

When war came in August 1914 the German plan was to defeat France quickly while the Eighth Army held East Prussia against Russia. Prit Buttar argues that the Eighth Army only needed to avoid defeat and keep its nerve until victory in the west was assured. Prittwitz had originally planned to hold the line of the Angerapp and let Rennenkampf suffer heavy losses attacking it.

The Russians had numbers but poor supply and communications. Rennenkampf's First Army was advancing from the east, and Samsonov's Second Army from the south. German aerial reconnaissance by Flieger Abteilung 16 found a gap between the two Russian armies, and radio intercepts suggested that Rennenkampf had halted to rest on 20 August.

On 17 August at Stallupönen, François's I Corps had beaten part of the Russian First Army, despite orders from Prittwitz to fall back to Gumbinnen. When he was told again at about 1 pm to break off, François is reported to have replied that he would do so when the Russians were defeated. After that success his scouts reported that the northern flank of the First Army was exposed, and he asked for the 2nd Division to attack, supported by XVII Corps and I Reserve Corps.

François argued that his troops, many of them East Prussians, would be demoralised by retreating from their homeland, and that the Russians were weaker than they looked; an uncoded Russian radio message seemed to support him. Prittwitz agreed, reluctantly. The result was a general attack on the morning of 20 August, before the Eighth Army had finished deploying.

The armies

The German Eighth Army had I Corps (François: 1st and 2nd Divisions), XVII Corps (Mackensen: 35th and 36th Divisions), XX Corps (Scholtz: 37th and 41st Divisions), I Reserve Corps (Below: 1st Reserve and 36th Reserve Divisions) and a cavalry division, according to the order of battle in the main source. XX Corps was in the south against Samsonov, so three corps and the cavalry faced Rennenkampf at Gumbinnen. The infobox gives the German strength as 74,400 with 224 machine guns and 408 guns.

Rennenkampf's First Army had 63,800 men in the same source, with 252 machine guns and 408 guns. The 3rd Corps (25th and 27th Divisions) stood at the centre. Cavalry under Huseyn Khan Nakhchivanski was supposed to cover the north but did not screen the 28th Division. The Russians had anticipated the German attack and moved up their heavy artillery.

The Germans had their own problems of command and discipline. François had disobeyed Prittwitz at Stallupönen, and Mackensen's and Below's corps were still moving up and were not ready for combat when François attacked. Below turned north to help Mackensen rather than advance on Goldap as ordered. The numbers are low next to the CDB90 figures (120,000 and 150,000) and neither set can be reconciled with the other, as the flags explain. What is clear is that on 20 August the Germans never fought as one army.

The battle

Prelude, Stallupönen, 17 August. Three days earlier François had held his ground against four Russian divisions (25th, 27th, 29th and 40th) that advanced without coordination and left a gap between the 27th and 40th. Falk's 2nd Division struck the flank of the 27th near Göritten, a frontal attack broke it, and it fled east. A counter-attack by the 29th Division then threatened to encircle François, and the Germans halted, did not exploit the success, and fell back to Gumbinnen, where Prittwitz later moved his other corps forward. That was the ground on which the main action opened.

François in the north, 3:30 am onwards. The 2nd Division made a night march and advanced through the Züllkinner Forest on the morning of 20 August. It outflanked the Russian 28th Infantry Division, which stood unprotected because the cavalry had not screened it, and inflicted about 60% casualties on it. It captured Mallwischken. The German 1st Division engaged the Russian 29th Infantry Division at 3:30 am. François's two divisions were largely successful.

Mackensen in the centre, 4:30 am onwards. Mackensen heard of François's success and attacked the Russian 3rd Corps (25th and 27th Divisions) at 4:30 am. The Russians had foreseen the attack and moved up their heavy artillery. The advance went well at first and then stalled under Russian artillery fire. The Russians turned the German flanks and Mackensen's men fell back in disorder to the Insterburg–Angerburg line, leaving about 6,000 prisoners in Russian hands. (One account names the 26th Division and the infantry order of battle the 36th; the main source does not reconcile them.)

Below in the south, from about noon. Below's I Reserve Corps was not able to join the fight until about noon. Instead of advancing on Goldap he turned north to help Mackensen. The Russian 30th Infantry Division attacked his flank. Neither side could advance and both lost heavily. Morgen's 3rd Reserve Division arrived too late to intervene.

The night. By evening the Eighth Army had a mixed result. François's corps had won, Mackensen's was effectively knocked out and had streamed back, and Below had stopped just short of a decisive success. Only Scholtz's XX Corps faced Samsonov's army in the south.

CDB90 times the fighting from 4 am to 4 pm on 20 August. Mackensen later felt that his corps had not been outfought and had withdrawn in good order without interference from the enemy, a view in tension with the above.

Aftermath

The German casualty figure is about 14,600 and the Russian about 18,800, with the Russians taking about 6,000 prisoners from Mackensen's corps. The battle was fought by a German army that attacked piecemeal and a Russian army that was ready for it.

The effect on German command was immediate. Reconnaissance showed that Samsonov's Second Army had five corps and a cavalry division, with six divisions about to cross the border towards Mlawa. Prittwitz telephoned Moltke and said he meant to retreat to the Vistula. Moltke was angry, since the Vistula retreat would let the two Russian armies unite. Prittwitz changed his mind and chose to attack Samsonov instead, a shift from facing east to facing south that the Germans had rehearsed in war games. François's I Corps and the 3rd Reserve Division moved by train to the west of XX Corps; I Reserve Corps and XVII Corps withdrew westward.

The Russians were slow to follow up. Samsonov was held back by poor railways and roads, and Rennenkampf pursued cautiously because of his losses and thin supplies. On 21 August Moltke decided to replace Prittwitz and his chief of staff, Georg von Waldersee. Hindenburg and Ludendorff took over on 22 August. Prittwitz was the first army commander dismissed in the war. The consequence, three days later, was Tannenberg.

Wargaming it

Gumbinnen is a good corps-level game, at a division or brigade per counter, over a single day on flat farmland and forest. The three German corps arrive in a different state and at different times, so the scenario is a test of coordination: François attacks too early, Mackensen is committed on the strength of his success, and Below goes the wrong way.

The most interesting rule is the uncoordinated German start. Give each corps its own activation and its own objectives, and let the German player decide whether to attack with I Corps alone, a limited attack, or to commit all three and risk a repeat of Mackensen's day. The Russian artillery, which the Russians moved up in anticipation of the attack, should punish the unprepared German advance. The 28th Division's open flank is a puzzle for the Russian player too, because the cavalry did not screen it.

The 'what if' questions are a pair. If Prittwitz had held on the Angerapp, as he first planned, would Rennenkampf have taken heavy losses attacking it? And if Prittwitz had stood after Gumbinnen, would Samsonov's slow advance have given him the time to fight both armies? A campaign-level game can take Gumbinnen as the first battle and the 21–22 August decisions as a second, with the dismissal of Prittwitz as a command event that changes the plan before Tannenberg.

Maps and pictures