The Second Battle of the Masurian Lakes was fought from 7 to 22 February 1915 on the Eastern Front of World War I. The Imperial Russian Army was caught up in a surprise Imperial German Army offensive in East Prussia as it planned its own assault into Germany, and the Germans destroyed the Russian army, which lost 200,000 of its 220,000 troops.
The fighting on the Eastern Front in 1914 had produced no decisive result. The Russians suffered defeats against the Germans but won victories over Austria-Hungary. Field Marshal Paul von Hindenburg and his Chief of Staff Erich Ludendorff, in East Prussia, argued for maximum resources to knock Russia out of the war. German Chief of the General Staff Erich von Falkenhayn did not believe Russia could be easily defeated, but agreed to stand on the defensive on the Western Front and transfer troops to the East.
By the start of 1915, Russia had pushed the Austro-Hungarians back to the Carpathian Mountains and was besieging the Galician fortress of Przemysl. The Russians had defeated Turkish forces at Sarikamish on the Caucasus front. They had, however, been forced to pull back behind Lodz in Poland.
In early 1915, the Russians and the Central Powers had more or less symmetrical plans for offensives. Rsusia aimed to strike against East Prussia in the north and through the Carpathian Mountains into Hungary in the south. Field Marshal Hindenburg and General Ludendorff planned a German offensive at the Masurian Lakes in East Prussia to coincide with an Austro-Hungarian offensive in the Carpathians.
The Central Powers struck first. At the Second Battle of the Masurian Lakes, launched in a snowstorm on 7 February, Hindenburg and Ludendorff attempted to trap the Russian 10th Army with a vast pincer movement. One Russian corps, finding itself encircled, surrendered en masse in the Augustow Forest, but the rest of the Tenth Army escaped, and the front restabilized.