The 'Battle of Brześć Litewski' (Brest-Litovsk) was a battle between German and Polish forces near the town of Brześć Litewski within the context of 'Weiss' (i) (14/17 September 1939).

After three days of heavy fights for the stronghold in the town of Brześć, the Germans captured the fortress and the Poles withdrew.

In the event of a German invasion, the Polish forces had initially not planned to defend the old fortress of Brześć. The town was located deep behind the Polish lines and was seen as a supply depot and organisation centre rather than a front-line fortress. However, after the 'Battle of Mława' and the 'Battle of Wizna', General Heinz Guderian’s XIX Corps (mot.) of Generaloberst Fedor von Bock’s Heeresgruppe 'Nord' broke through the Polish lines and advanced at high speed to the south with the aim of outflanking Warsaw from the east and cutting western Poland in two.

According to the secret protocol of the Molotov-Ribbentrop Pact of 23 August 1939, the region of Brześć was assigned to the Soviet 'sphere of influence'. However, the Soviet forces did not begin their invasion of eastern Poland until 17 September, and had the rapidly advancing German corps stopped, it would have given the Poles the time in which to regroup and prepare. Already, on 8 September, the German foreign minister, Joachim Ribbentrop, notified the Soviet government that the German forces would have to violate the Soviet 'sphere of influence'.

The fortress town of Brześć lies on the confluence of the Muchawiec and Bug rivers. Occupying the site of a mediaeval castle, the fortress had been reconstructed and strengthened in Napoleonic times and then again in 1847. Heavily damaged during World War I, the fortress was turned into a matériel depot and its central part into a prison. Although largely obsolete by contemporary standards, the fortress occupied a strategic position in the Polish lines and its defence could prevent German forces from crossing Polesia into Lesser Poland and Galicia to the south.

The aim of the XIX Corps (mot.) was to seize the fortress in order to prevent elements of General brygady Czesław Młot-Fijałkowski divided Independent Operational Group 'Narew' from retreating to the south and linking with other Polish forces. The German forces consisted of an entire armoured corps: Generalleutnant Leo Freiherr Geyr von Schweppenburg’s 3^rd Panzerdivision, Generalleutnant Paul Bader’s 2^nd Division (mot.) and Generalleutnant Mauritz von Wiktorin’s 20^th Division (mot.).

At the end of the summer of 1939, the fortress accommodated the march battalions of 82^nd Regiment and 35^th Regiment as well as elements of several smaller units. Moreover, large numbers of newly mobilised reservists began to assemble at the fortress as they awaited forward deployment to their units. From these units Generał brygady Konstanty Plisowski organised a force of some three infantry battalions, supported by an engineer battalion, several batteries of artillery and Nos 112 and 113 Companies of old FT-17 light tanks used for training.

Brześć was thus defended by a small improvised force under the command of Plisowski, and in addition to the forces enumerated above also had the PP53 and PP55 armoured trains commanded by Kapitan Andrzej Podgórski and Kapitan Mieczysław Malinowski.

On 14 September, 77 tanks of the 2/8^th Panzerregiment, part of Generalleutnant Ferdinand Schaal’s 10^th Panzerdivision, part of the Heeresgruppe 'Nord' reserve, reached the area of Brześć and attempted to capture the fortress off he march. The probe attack was repelled by Polish infantry and No. 113 Company of 12 obsolete Renault FT-17 light tanks. All the Polish tanks were destroyed, but the German forces were forced to fall back to their initial positions. The PP53 armoured train, which made a reconnaissance advance to Wysokie Litewskie, was attacked by a reconnaissance patrol of the 10^th Panzerdivision, and its crew opened fire with the train’s artillery. Several other skirmishes were fought, but were largely inconclusive.

Later that day the German artillery arrived and began a bombardment of both the fortress and the town, and there followed severe street fighting. At dawn about half of the town was in German hands, and the other half was still being defended by Polish infantry. Polish anti-tank weapons, artillery and anti-aircraft guns were very scarce, and were unable provide adequate support for the infantry. The following day Polish defenders withdrew from the town, but heavy casualties on each side prevented the Germans from continuing their attacks on the fortress. Instead, it was constantly shelled by the artillery and bombed by the Luftwaffe.

When reports informed Plisowski that reconnaissance elements of the 3^rd Panzerdivision had been sighted near the railway station at Żabinka, to the north of Kobryń, he sent PP55 to prevent his forces from being cut off. A platoon of five scout tanks left the train near Żabinka and attacked German armoured cars near a bridge over the Muchawiec river. After three tanks had been lost, the two surviving vehicles withdrew. Another attack by an assault platoon from the train failed. After a combined attack by the assault platoon and PP55’s guns, the Germans left the area of the Muchawiec river bridge. When they returned, PP55 attacked another battle group of the 3^rd Panzerdivision, comprising reconnaissance elements and the 5^th Panzerregiment supported by the 6^th Batterie of the 75^th Artillerieregiment. After destroying a few armoured cars, the train withdrew towards Brześć and the train station was left in German hands.

The main German assault got under way early in the morning of 16 September. The defenders had a good supply of small arms ammunition and light weapons from the munitions depot in the fortress, but had almost no anti-tank weapons and insufficient artillery cover.

Although the German infantry was repelled and the assault of German tanks was stopped by two FT-17 tanks which sealed the fortress’s northern gate, by the fall of night it had become clear that the German pressure had rendered the entire Polish situation very grave. Despite heavy losses, the 20^th Division (mot.) and 10^th Panzerdivision captured the northern part of the citadel. Meanwhile, the combined 3^rd Panzerdivision and 2^nd Panzerdivision comprising Generaloberst Ewald von Kleist 's XXII Corps (mot.) entered the area. The Poles were unable to resupply and their casualties rose to almost 40%.

At dawn Plisowski ordered part of the Polish forces to retreat from the easternmost fortifications and regroup on the other side of the river and farther to the south. The evacuation had been completed by a time early in morning of 17 September, when the last unit crossing the bridge blew it to hinder the Germans. An hour later elements of the 76^th Infanterieregiment entered the fortress in the face of only vestigial opposition.

On 17 September Soviet forces crossed the Polish border and started a rapid advance to the west. The Soviet 29^th Tank Brigade, under the command of Kombrig Semyon Krivoshein reached the area of Brześć later on the same day and took over the fortress from the Germans in a ceremonial parade after which the German forces left the area, crossed the Bug river and started their pursuit of Plisowski’s retreating forces.

Some 25 miles (40 km) to the east the Polish improvised 'Kobryń' Division under Epler’s command was ordered to retreat in tandem with Plisowski’s force. After the 'Battle of Kobryń' the division evaded encirclement and linked with Plisowski’s force. The Polish forces were soon joined by the 'Podlaska' Cavalry Brigade and together started to make their way toward Lwów and the Romanian 'bridgehead'. Under command of Kleeberg, these forces formed the bulwark of the remaining Polish army, fighting effectively against both the Germans and the Soviets until the 'Battle of Kock' that ended on 6 October.

As noted above, the Brest fortress was handed over to the Soviets in accordance with the Molotov-Ribbentrop pact, but was besieged and captured again by the Germans at the start of 'Barbarossa' in 1941.