The Battle of Grodno took place between 20 September and 22 September 1939, during the Soviet invasion of Poland. It was fought between improvised Polish units under Gen. Wacław Przeździecki and Soviet Red Army troops of Komkor Ivan Boldin's Dzerzhinsky Cavalry Mechanized Group, 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 Tank 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. In the interwar period, Grodno was one of the strongest garrisons of the Polish Army. The commands of District Corps No. 3 and the 29th Infantry Division were quartered there, as were two infantry regiments and one light artillery regiment. Beginning in January 1938, the District Corps No. 3 was commanded by brigadier general Józef Olszyna-Wilczyński. In August 1939, after the mobilization, the 29th infantry regiment under command of colonel Ignacy Oziewicz was sent to the region of concentration of "Prusy" Army. From the excess of troops there was formed the Operational Group "Grodno" (about 7 thousand soldiers) with a goal of defending western and northwest sides of the city. Nonetheless, on 10 September OG was disbanded and the best troops were sent for defense of Lwów. Up to 12 September, the certified leader of the Fortified Zone of Grodno was colonel Bohdan Hulewicz, who made orders for defense of the city, however, against German troops. One of his crucial decisions was to create a stock of bottles with highly flammable mixture. Soldiers and volunteers were trained in using these. Grodno had been suffering from warfare since 1 September. That day, German bombers destroyed weaponry storehouses and military warehouses by Karolin. Roughly half of the city's military equipment and ammunition were destroyed this way. There were also casualties, and the attacks continued. On 17 September, as a result of rumours about Soviet aggression on Poland, a communist sabotage happened to the city, which was however suppressed quickly. On 18 September, general J.Olszyn-Wilczyński arrived to the city