The second battle of the Masurian Lakes, 7-21 February 1915 (also know as the Winter Battle in Masuria) was part of an over-ambitious German and Austrian plan designed to cut off the Russian armies in Poland. This involved an Austro-Hungarian attack in Galicia, towards Lemberg, and a German attack from East Prussia. It was hoped that the two pincers could meet east of Warsaw. Hindenburg and Ludendorff, the German commanders in the east, were not convinced by the grand plan, but did think they could destroy the Russian Tenth Army.
Despite the stunning German victories at Tannenburg and first Masurian Lakes in 1914, the Russian Tenth Army (General Sievers), was still on German soil, occupying a line just to the east of the Masurian Lakes. Four Russian corps held the line (from north to south they were III, XX, XXVI and III Siberian corps).
The Germans allocated two armies to the offensive. To the north was a new Tenth Army (General Hermann von Eichhorn), of three corps, while in the south and centre of the line was the experienced Eighth Army (General Otto von Below). The German plan was for the Tenth Army to swing around the Russian lines to the north, the Eighth to the south, and for the Russians to be trapped west of the Niemen River.
The right wing of the Eighth Army attacked first, on 7 February, towards Lyck. By February 10 the Russians had been forced back most of the way towards that town, but it would take the Germans another four days to capture the town.
The German Tenth Army attack began on 8 February. By 10 February it had advanced twenty five miles and by 12 February close to fifty. It had achieved most of its objectives. Having started off faced to the east, it was now facing south, with three of the four Russian corps to its south. The Russian III corps had managed to escape to the east, towards the fortresses of Kovno and Olita on the Niemen River.
That left three Russian corps in danger of being trapped. Their resistance at Lyck allowed the III Siberian corps to escape to the south east. By the night of 15 February, XXVI corps was also safe, having slipped away towards Grodno. All three Russian corps had suffered heavy casualties, and were in a state of disarray, but had escaped the trap.
XX corps was not so lucky. It had fought a determined rearguard action in the Forest of Augustow, but on 14 February the German XXI corps had been sent on a dangerous march to the east of the forest. By 18 February, despite attacks from both sides of its line of march, XXI corps had closed the last gap on the eastern side of the forest. The Russian XX corps was trapped. On 21 September the 30,000 survivors of XX corps surrendered to the Germans.
The Russians lost 200,000 men during the battle, 100,000 of them prisoners. German losses were comparatively light, but two weeks of fighting in the freezing cold and snow of East Prussia and Russia had exhausted them. The surrender of XX corps marked the end of the battle.
The battle had been a great tactical victory, but even Hindenburg admitted that it had been a strategic failure. Three of the four Russian corps had escaped, although only after suffering massive casualties, and the Russian line had been restored. The wider plan had also failed. The Austro-Hungarian attack in Galicia ended in failure, and with the loss of the great fortress of Przemysl.