were held in reserve. The German southern thrust was to be made by Below's Eighth Army, with the XL Reserve Corps deployed west of Johannisburg, and the XX Corps at Ortelsburg. The Russian Tenth Army consisted of the III Corps opposite Eichhorn, and the III Siberian Corps opposite Below, while the XX Corps and XXVI Corps held the center. Battle Chief of the German Great General Staff Erich von Falkenhayn strongly believed that the war would be won on the Western Front. Nonetheless, he sent four additional army corps to Paul von Hindenburg, commander of their Eastern Front. By February 1915, thirty-six percent of the German field army was in the east. German Ninth Army attacked from Silesia into Poland at the end of January; they released tear gas, which stopped their assault by blowing back on the attackers. The Russians counterattacked with eleven divisions under a single corps commander, losing 40,000 men in three days. In East Prussia, further Russian incursions were blocked by trench lines extending between the Masurian Lakes; they were held by the German Eighth Army, commanded by General Otto von Below. The Eighth Army was reinforced by some of the newly arrived corps, while the rest of them became the German Tenth Army, commanded by Colonel-General Hermann von Eichhorn, which was formed on the German left. The Tenth Army was to be one wing of a pincers intended to surround their opponents: General Sievers' Russian Tenth Army. A new Russian Twelfth Army under General Pavel Plehve was assembling in Poland roughly to the southwest. Sievers warned the Northwest Front commander, General Nikolai Ruzsky, that they were likely to be attacked, but was ignored. On February 7, despite a heavy snowstorm, the left wing of Below's Eighth Army launched a surprise attack against Sievers, whose trenches were shallow, disconnected ditches, with little or no barbed wire because the first shipments had not arrived until December 1914. The following day, the German Tenth Army also drove forward. Snow, with drifts as high as a man, slowed German progress down the roads for the first two days; off the roads, the ground was too boggy for fighting. Despite these formidable obstacles, the German pincers advanced in a week, inflicting severe casualties on the Russians. Sievers' ordered Evgeny Radkevich's III Siberian Corps to pull back to Lyck, where it would form a new defensive line with the XXVI Corps.