The Masuria-Augustów operation of 1915 (in German literature called theWinter Battle in Masuria of 1915, and in Russian literature - the Augustów opera-tion of 1915). The operation of the German troops of the Tenth and Eighth Armies- altogether 250,000 soldiers, against the Russian Tenth Army commanded by Ge-neral F. W. Siwers which equaled German forces in number. German commanderHinderburg (Chief German Commander in the East), but in fact its headquarters'commander Ludendorff, decided to use classic double envelopment according to theCannae's scheme against the Russian troops. The German Tenth Army commandedby General G. Eichhorn was supposed to attack the northern wing of the RussianTenth Army whereas the German Eighth Army commanded by General Otto vonBelow - the southern wing. Both German Armies were to surround and destroythe Russian Tenth Army. Its commander Siwers, in consequence of bad work doneby the army reconnaissance patrol was not aware of the fact that the Germanswere preparing the winter offensive in Masuria. He started to launch the Lasdenyoperation which had been prepared earlier on his right wing. It commenced on 25th January 1915 on the right wing of the Russian Army. It was not successful andled to the prolongation of the front line by another 35 km and weakening of theRussian forces. On the 7th February, the German Eighth Army started attackingtowards Augustów whereas the Tenth Army attacked towards Wierzbolowo andSuwalki. On 17th February, after severe battles near Lyck (Elk) against III Sibe-rian Corps of General Radkiewicz, the German Eighth Army captured Augustów.The encirclement of the entire Russian Tenth Army failed but on 21st February1915, in the Augustów Primeval Forest, XX Russian Corps of General Bulhakowwas surrounded and captured to slavery (app. 24,000 soldiers). The fact that theGermans focused their attention on encircling the XX Russian Corps gave extratime to other corpses and allowed them to avoid a tragic lot of General Bulhakow and the forces under his command. These corpses safely withdrew towards the lineKowno-Osowiec. The Osowiec fortress played an important role in this struggle. It was located in the gap which formed between the Tenth and Twelfth Russian Armies. The Germans could not pass it over and go further. It was under siege from 17th February to 3rd March 1915 and the German troops could not captureit even though they had rich experience in capturing the fortresses in Liege and Namur in Belgium.