The fortress of Kaunas was one of the strongest land fortresses of the Russian Empire at the end of the XIXth - the beginning of the XXth century. At the beginning of World War I, Kaunas passenger and merchant ships were passed over to the staff of the Kaunas fortress. The army coated two steamboats - the "Jaroslavna" and the "Venera" [Venus] - with armourplates and armed them. On the 13th of May, 1915, the steamboat "Jaroslavna" took part in the battle with the German army, and the "Venera" steamboat joined the battle soon after. With respect to individual missions, the participation of such steamboats in the defence of Kaunas fortress in 1915 often yielded positive results. In the Lithuanian military history this was the only case when armed steamboats took part in the battles on the Nemunas River.