The 'Battle of Grodno' was a small battle between Soviet and Polish troops during the Soviet invasion of eastern Poland (20/22 September 1939).

The battle was fought between improvised Polish units under General brygad Wacław Przeździecki and Soviet troops of Komkor Ivan Boldin’s 'Dzerzhinsky' Cavalry Mechanised Group at the time of the non-aggression agreement between the USSR and Germany under the terms of the Ribbentrop-Molotov Pact which made it possible for Soviet forces to enter and take eastern Poland as the Germans took the country’s western areas in 'Weiss' (i).

The Soviet aggression found much of 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 Polish defences of the Border Defence Corps, the Soviet XV Tank Corps started a fast advance toward the city of Grodno. The commander of the pre-war Grodno Military Area Command, Generał brygady Józef Olszyna-Wilczyński, together with the mayor of Grodno, Roman Sawicki, started to organise the city’s defences, based mostly on mobile battalions, volunteers, boy scouts and policemen.

During the period between the two world wars, Grodno had boasted one of the strongest garrisons of the Polish army. The headquarters of District Corps No. 3 and the 29^th Division were located in the city, as were two infantry regiments and one light artillery regiment. From January 1938, District Corps No. 3 was commanded by Olszyna-Wilczyński, and in August 1939, after the Polish mobilisation, Pułkownik Ignacy Oziewicz’s 29^th Regiment was sent to the concentration area of the 'Prusy' Armia, and otherwise surplus troops, numbering some 7,000 men, were grouped as the Operational Group 'Grodno' for the task of defending the western and northwest sides of the city. On 10 September this operational group was disbanded and the best troops were despatched to bolster the defences of Lwów. Up to 12 September, the commander of the Fortified Zone of Grodno was Pułkownik Bohdan Hulewicz, who organised the city’s defences, albeit against a German rather than Soviet threat. One of Hulewicz’s crucial decisions was the creation of a stock of bottles containing a flammable mixture, and both soldiers and volunteers were trained in their use.

Grodno had been involved in 'Weiss' (i) since 1 September. On that day, German bombers attacked armouries and military warehouses in the Karolin area, and about half of the city’s military equipment and ammunition were destroyed. There were also casualties, and the attacks continued. On 17 September, as a result of rumours about Soviet aggression on Poland, a communist-inspired sabotage effort took place in the city, but this was quickly suppressed. On 18 September, Olszyn-Wilczyński arrived from Pińsk, but believed that the city could or rather should no longer be defended, and he therefore ordered some of the troops to retreat into the region of Sopoćkiń and Kalet to cover forces moving into Lithuania. On the same day, the commander of the District Corps No. 3 left the city without appointing any officer responsible for further defence. District head Walicki and president of the city Cieński also departed. Another wave of communist supporters now emerged, and on this occasion took over Batory square in the city centre. The 31^st Guard Battalion snt its alert platoon into action, resulting in the elimination of the threat. Poles mounted machine guns on the towers of the city’s nearby churches.

Przeździecki’s Grodno Defence Group included Generał brygady Edmund Heldut-Tarnasiewicz’s 'Wołkowysk' Cavalry Brigade, Generał brygady Stanisław Szostak’s 32^nd Armoured Reconnaissance Group, and the 94^th Artillery Battery.

Boldin’s 'Dzerzhinsky' Cavalry Mechanised Group included the VI Cavalry Corps (4^th, 6^th and 11^th Cavalry Divisions), the V Corps (4^th and 13^th Divisions) and the XV Tank Corps. This last, which was commanded by Komdiv Mikhail P. Petrov, included Kombrig Alekei V. Kurkin’s 2^nd Tank Brigade, Polkovnik Ivan I. Yushchuk’s 27^th Light Tank Brigade and Polkovnik Berdnikov’s 20^th Motorised and Machine Gun Brigade. The Soviet force also included the 21^st Tank Brigade.

Poorly equipped, under strength and lacking any anti-tank artillery, the Polish defenders relied mostly on improvised anti-tank means such as bottles filled with petrol or turpentine, small arms and anti-tank obstacles. On 20 September, the tanks of the 27^th Light Tank Brigade of the XV Tank Corps reached the city’s outskirts. Although both numerically and technically superior, the Soviet forces lacked infantry support and were short of fuel, which brought many of the tanks to a halt. Also, the tank crews had no experience in urban warfare, which was a significant advantage for the defenders.

The Soviets tried to seize the city from the south across the bridge over the Niemen river, but the initial assault was repelled. Early in the morning of 21 September, the defenders were joined by the remnants of a reserve unit, the 'Wołkowysk' Cavalry Brigade under Generał brygady Wacław Przeździecki. After two days of heavy fighting, often at 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 to the north in the direction of the nearby Lithuanian border.

According to Soviet sources, the Soviet forces suffered casualties of 57 men killed and 159 men wounded, but Polish historians have claimed that the Soviets lost some 800 men killed, missing or wounded. They also lost 19 tanks and four armoured cars.

Polish losses, both civilian and military, remain unknown, although Soviet records claim 644 men killed and 1,543 men taken prisoner (66 officers and 1,477 men). The Soviet troops reported the capture of 514 rifles, 146 machine guns, one mortar, and one of the Poles two anti-aircraft guns.

After the battle, the 'Wołkowysk' Cavalry Brigade’s remaining strength broke through the lines of the 2^nd Light Tank Brigade's reconnaissance battalion 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.