On August 8, 1915, the attack on Kovno was begun. At the same time the German forces advanced against Lomza and still farther south advanced nearer and nearer to the Warsaw-Bialystok-Vilna-Petrograd railroad, their main objective for the present. All these advances found serious opposition at the hands of the Russians, who successfully attempted to hold up the enemy everywhere in order to insure the safety of their retreating armies. On August 10, 1915, the Russians attempted an unsuccessful sortie from Kovno. Farther south, as far as Lomza, the Russian forces continued their retreat, fighting continuous rear-guard actions for the purpose of delaying the hard-pressing enemy, who, however, gradually came closer and closer to the Nareff-Bobr line. Of course the losses on both sides throughout this continuous fighting were severe. The Russians lost thousands of men by capture, for although they succeeded in withdrawing, practically intact, the principal parts of their armies before the Germans could come up in strong enough numbers to risk attacks, smaller detachments here and there lost contact with the main body and fell in the hands of the Germans and Austrians, so that there passed hardly a day when the official reports did not contain some claims about a few thousand men having been captured.
South of the Niemen the Russians attacked Von Eichhorn's army along the Dvina River, but were thrown back with severe losses. On August 11, 1915, Von Scholtz's group occupied the bridgehead at Vilna, which had been stubbornly defended until the Russian retreat had progressed far enough to make its further possession unessential. The same forces succeeded in crossing the Gac River, south of the Nareff, capturing during three days' fighting almost 5,000 men. Von Gallwitz with his army stormed on the same day Zambroff and then pressed on through Andrzejow toward the east. South of the Nareff, toward the Bug and Brest-Litovsk, the fighting continued throughout the following days. Wherever possible the Russians resisted, and every little stream was used by them to its utmost possibilities in delaying the advance of the enemy. On August 13, 1915, a strongly fortified position in the Forest of Dominikanka fell into German hands. On the same day an outlying fortified position north of Novo Georgievsk had to surrender and other forces fighting between the Nareff and Bug reached the Slina and Nurzets Rivers. The latter was crossed late on August 15, 1915, after the most severe kind of fighting.