Lodz fell on December 6, 1914. On the 7th the Russians were again repulsed in the Mazurian Lakes region. Throughout that month and January, 1915, very severe fighting took place in the Carpathian Mountains, and by the end of January, 1915, the Austro-Hungarian forces were in possession of all the passes, but had not been able to drive the Russians from the north side of the mountains. In the meanwhile the Russians were pressing their attacks against East Prussia with renewed vigor and greatly augmented forces, and by February 7, 1915, had again advanced to the Mazurian Lakes. In a battle lasting nine days, Von Hindenburg once more defeated the Russian army and drove it back into North Poland, inflicting very heavy losses. At the end of another week, February 24, 1915, the Russians had been driven out of the Bukowina. Von Hindenburg had followed up his new success at the Mazurian Lakes with a drive into North Poland, undoubtedly with the object of invading Courland. Hardly had it gotten under way when the Galician fortress of Przemysl was forced to surrender on March 22, 1915. This not only gained for the Russians a large booty in prisoners, munitions, and equipment, but also released the great army that had been besieging the fortress. It was thrown immediately against the Austro-Hungarian forces in Galicia, who were driven back again rapidly into the Carpathian Mountains. Again Austria appealed to Germany for help. General von Mackensen was sent to the rescue with an army made up largely from troops taken from Von Hindenburg's forces. Thereby the latter again was forced to stop further operations in the north. Von Mackensen's combined Austro-Hungarian-German armies had an immense supply of guns and munitions, both of which were beginning to run short in the Russian army. With these they blasted away Russian line after line, driving the Russians finally almost completely out of Galicia, after retaking Przemysl on June 3, 1915, and Lemberg on June 24, 1915. In the north, in the meantime, the Germans had received reenforcements filling the gap that Von Mackensen's Galician operations had caused. With these they invaded Courland while other forces landed on the Gulf of Riga. With these two groups they pushed south and soon connected with Von Hindenburg's army before Novo Georgievsk and Warsaw. The latter had been there practically ever since early in January, 1915, when after the fall of Lodz it had gradually advanced against Poland's capital, but was held within seven miles of it along the Bzura and Rawka Rivers, where many bloody engagements were fought.