Masurian Lakes, battle of (1914). The destruction of the Russian Second Army at Tannenberg left another Russian army deep in East Prussia, with the Germans badly out of position to deal with it. Even before the last Russian prisoners were counted in the south, Ludendorff, Hindenburg, and their brilliant operations officer Max Hoffmann began co-ordinating redeployment. Eighth Army, reinforced by two corps drawn from the western front during the Tannenberg crisis, now consisted of thirteen divisions, two cavalry divisions, and about five more divisions' worth of fortress and garrison troops. The Russian First Army, under Gen Pavel Rennenkampf, had fourteen divisions, a rifle brigade, and five cavalry divisions. Supporting it on the left, moving into the hole created by Second Army's defeat, was a new Tenth Army with the equivalent of a half-dozen first-line divisions—and more en route.
Eighth Army's command team saw their best chance as concentrating against First Army's left wing, in the air since Tannenberg. The German operational concept was based on a right hook through the Masurian Lakes, driving north-east against the Russian lines of communication while the rest of the army fixed the Russians in place by a frontal attack. Rennenkampf had held his ground partly because he did not believe the Germans could redeploy as quickly as they did. Instead, replicating their earlier performances, the Eighth Army staff and the railways within a week mustered eight divisions on First Army's front and five more, with two cavalry divisions, for the flank attack.
This relatively even division of forces suggests willingness to accept Russian retreat, as opposed to thinking in terms of a Cannae or a Chancellorsville. On 7 September, three divisions drove in the Russian left against scattered opposition, but the cavalry, blocked by the leading units' supply trains, could not get forward. The XVII Corps, expected to support the initial advance, was stopped by determined Russian resistance, as were the four corps that went against the First Army's front. The flank attack's commander responded on his own initiative by swinging two of his divisions hard left, routing the Russians in front of XVII Corps. The way to First Army's rear seemed open, but Rennenkampf reacted with an energy and decision in sharp contrast to his earlier lethargic behaviour. On 10 September he committed two divisions to a counter-attack that bought the rest of his army time to disengage.
Marching over 20 miles (32 km) a day in brutally hot weather on roads blocked by their own transport, the Russians managed to run faster than the Germans could chase them. Ludendorff, expecting a general battle, kept his flanking force close to the main army on the 10th. Given more latitude on the 11th, they were too tired and too disorganized to do more than push the Russians across the frontier in the face of determined rearguards. The Russian Tenth Army made no significant effort to intervene. By 14 September, the battle of the Masurian Lakes was over. The Russians had lost over 125, 000 men and around 200 difficult-to-replace guns. They had not lost the war. Having defeated two armies in a month, the Germans would find they had not yet begun to fight in a theatre that, from first to last, gave nothing back.
— D. E. Showalter
