the Russian First Army. Hindenburg's tactics spurned head-on attacks all along the front in favor of schwerpunkte: sharp, localized hammer blows. Two schwerpunkte struck in the First Battle of the Masurian Lakes. Two columns drove east from these breakthrough points to pocket the Russians led by General Paul von Rennenkampf, who managed to retreat with heavy losses. In the first six weeks of the war the Russians had lost more than 310,000 men. Eight hundred thousand refugees were able to return to their East Prussian homes, thanks to victories that strikingly contrasted with the bloody deadlock of the Western Front following the failure of the Schlieffen Plan. Partnership with Ludendorff The Hindenburg-Ludendorff duo's successful performance on the Eastern Front in 1914 marked the beginning of a military and political partnership that lasted until the end of the war. As Hindenburg wrote to the Kaiser a few months later: "[Ludendorff] has become my faithful adviser and a friend who has my complete confidence and cannot be replaced by anyone." Despite their strikingly dissimilar temperaments, the older general's calm decisiveness proved to be an outstanding fit for Ludendorff's energy and tactical ingenuity. When Ludendorff's nerves twice drove him to consider changing their plans for Tannenberg at the last minute; both times Hindenburg talked to him privately and his confidence wavered no further. Defending Silesia On the east bank of the Vistula in Poland the Russians were mobilizing new armies which were shielded from attack by the river; once assembled they would cross the river to march west into Silesia. To counter the Russians' pending invasion of Silesia, Hindenburg advanced into Poland and occupied the west bank of the Vistula opposite from where Russian forces were mobilizing. He set up headquarters at Posen in West Prussia, accompanied by Ludendorff and Hoffmann. When the Russians attempted to cross the Vistula, the German forces under his command held firm, but the Russians were able to cross in the Austro-Hungarian sector to the south. Hindenburg retreated and destroyed all railways and bridges so that the Russians would be unable to advance beyond west of their railheads—well short of the German frontier. On 1 November 1914 Hindenburg was appointed Ober Ost (commander in the east) and was promoted to field marshal. To meet the Russians' renewed push into Silesia, Hindenburg moved Ninth Army by rail north to Thorn and reinforced it with two corps from Eighth Army.