Battle of Grodno ( 1939 ) The Battle of Grodno took place between 21 September and 24 September 1939 , during the Soviet invasion of Poland . It was fought between improvised Polish units under Gen . Wacław Jan Przeździecki and the Red Army of the Soviet Union , at the time in a non - aggression agreement with Nazi Germany under the Ribbentrop - Molotov Pact . Prelude . The Soviet aggression caught much of the eastern Poland virtually undefended , as most of the Polish forces from the area had already been transferred to the German front . After breaking through overstretched defences of the Border Defence Corps , the Soviet 15th Armoured Corps started a fast advance towards the city of Grodno . Commander of the pre - war Grodno Military Area Command Gen . Józef Olszyna - Wilczyński , together with the mayor of Grodno Roman Sawicki , started organizing city defences , based mostly on march battalions , volunteers , Boy Scouts and police forces . The battle . Ill - equipped , undermanned and lacking any anti - tank artillery , the Polish defenders relied mostly on improvised anti - tank means such as bottles of gasoline or turpentine , small arms fire and anti - tank obstacles . On 20 September , the Soviet tanks of the Soviet 27th Armoured Brigade of the 15th Armoured Corps reached the city ' s outskirts . Although both numerically and technically superior , the Soviet forces lacked infantry support and oil , which stopped many tanks . Also , the tank crews had no experience in urban warfare , which was a significant help for the defenders . The Soviets tried to seize the city from the south through the bridge over the Niemen River . However , the initial assault was repelled . In the early morning of 21 September , the defenders were joined by the remnants of the reserve Wołkowysk Cavalry Brigade under Brigadier General Wacław Przeździecki . After two days of heavy fighting , often in close quarters , much of the city centre was destroyed by Soviet artillery . Seeing no chance for further defence , on 22 September the remainder of the Polish forces withdrew towards the Lithuanian border . According to Soviet sources , the Red Army suffered casualties of 57 killed and 159 wounded . However , Polish historians , Andrzej Krzysztof Kunert and Zygmunt Walkowski claim that the Red Army lost around 800 killed , missing or wounded . They also lost 19 tanks and four armored cars . Polish losses , both civilian and military , remain fully unknown , although Soviet records do exist - 644 killed , 1 , 543 captives ( 66 officers and 1 , 477 soldiers ) plus salvages : 514 guns , 146 machine guns , one mortar , one anti - aircraft gun . Aftermath . After the battle , the remaining forces of the Wołkowysk Cavalry Brigade broke through the lines of the recce battalion of the 2nd Armoured Brigade in the Battle of Kodziowce and headed for the Augustów Forest . About 300 Polish defenders of the city , including teenage boys , were murdered by the Soviets after the Battle . The victims were both Polish students ( 20 ) and soldiers ( 30 ) as well as an unknown number of civilians . Poles were judged by the Soviet justice organs for their participation in the defense of the city and were reproached with the participation in the armed resistance movement against the Red Army and sentenced .