Offensives on a large scale such as that which had been prevented by the "Winter Battle of the Mazurian Lakes" were not attempted by the Russians on their northern wing after the short counterattack that had pushed their lines into the Mlawa angle in the corner of the Vistula and the Prussian boundary beyond Przasnysz, to the east of Thorn. They virtually remained in their strongly fortified positions along the Narew, the Bobr, and the Niemen, except for the sending out of occasional attacking columns against the German lines lying opposite to them. These forward thrusts were made especially from the fortresses Grodno and Kovno, and the fortified place Olita. We have already dealt with one such operation which came to grief in the forest of Augustowo in March. The German invasion of Courland had taken place, and the extension of the German lines to the north invited a thrust at their communications when, in the middle of May, the Russians attempted to break through the German lines with columns starting from the great forest to the west of Kovno. Here German troops under General Litzmann, acting under the command of General von Eichhorn, stood on guard. When Litzmann received information that the Russians were advancing in force he was obliged hastily to gather such troops as he could find to stem the Russian attack. Troop units from a large variety of different organizations were freshly grouped practically on the battle field. At Szaki and Gryszkabuda, on May 17-20, they struck the Russians with such force that the Slavs were driven back into the forests. The German general now decided to clear this territory of his enemies, as it had given them a constant opportunity for the preparation of moves which could not be readily observed, because of the protection of the thick woods. Again he executed the favorite maneuver of Von Hindenburg's armies. He gathered as heavy a weight of troops as possible on his left wing and pushed them forward in an extended encircling movement. From the south a strong column from Mariampol and the line of the Szsczupa moved upon the fortified position of the Russians and the southern corner of the great forest, meeting with strong resistance at Dumbowa Ruda. The troops moving down from the northern part of the woods swung to their right to cut off the Russians from their retreat toward Kovno. By the time the operations had reached this stage it was the second week in June, 1915, and in the great pine forests extending for miles there was an oppressive heat with perfect absence of breeze. Three Russian positions lying in the river valleys in the forest were encircled one after another from the north and had to be given up.