The shattering of the Tenth Russian Army in the "winter battle" of the Mazurian Lakes was part of a greater conflict which in February, 1915, extended far down the armies on the right flank of the great Russian battle line which ran from the Baltic to the Dniester. A "new gigantic plan" of the Slavs was involved. As interpreted by the German General Staff it meant that while the extreme northern wing of the Russian armies was to sweep westward through the projecting section of Germany, East Prussia, along the Baltic another Russian army was to advance in force from the south against the corner formed by West Prussia and the Vistula. With vast masses of cavalry in the van, it was to break through the boundary between Mlawa and Thorn, and pushing northward, come into the rear of those German forces which were facing eastward against the attack aimed at East Prussia from the northeast. For operations in this section the Russians had favorable railway connections. Two railways terminating at Ostrolenka permitted the rapid unloading of large masses of troops at this point, and the line Warsaw-Mlawa-Soldau led straight into the territory aimed at by such an invasion. It seemed easily credible that the Russian commander in chief did, as reported, give orders that Mlawa should be taken be the cost what it might. The northern Russian armies based upon the fortresses of Kovno and Grodno on the Niemen had not fully started on their part of this great, well-planned undertaking when the German counteroffensive was suddenly launched with tremendous strength from the Tilsit-Insterburg-Mazurian Lakes line. The disaster which followed, and which banished all hope of an advance of the Russians on this wing, has been described on a preceding page. While the Germans, using to the best advantage their net of railroads for the swift accumulation of troops, had gathered large forces on the Mazurian Lakes line, they had at the same time strengthened the troops standing on the southern boundary of West and East Prussia. An artillery officer, General von Gallwitz, was placed in command of this army with orders to protect the right flank of the German armies attacking in Mazurian Land, and to prevent the expected Russian attempt at invasion in his own sector of the front. While the "winter battle" was raging to the east of him, Von Gallwitz in the characteristic German fashion of defense by a strong offensive moved forward up the right bank of the Vistula to Plozk. A cavalry division and regiments of the Guard at Sierpe and Racionz, February 12-18, 1915, won well-earned laurels for themselves by driving an enemy of superior strength before them. At Dobrin, according to German report, they took 2,500 prisoners.