The Battle of the Bzura was fought from 9 to 22 September 1939, the largest battle of the German invasion of Poland2. The Polish armies Poznań and Pomorze, under General Tadeusz Kutrzeba, struck the flank of the German 8th Army on the Bzura river3 and at first drove it back, delaying the attack on Warsaw. German reinforcements and air power then surrounded the Polish forces, and most were destroyed or captured, though some fought their way through to Warsaw and Modlin.
In the second week of September 1939 the German armies were racing toward Warsaw. Behind their left flank, two Polish armies that had withdrawn from the west were still intact. On 9 September General Tadeusz Kutrzeba turned them south across the Bzura river, in the largest Polish counterattack of the campaign.
Two armies cut off
When Germany invaded on 1 September, the Polish Poznań Army and Pomorze Army in western Poland were bypassed as German columns drove toward Warsaw. By early September they were withdrawing east, threatened with being cut off, while the German 8th Army under Johannes Blaskowitz marched past their southern flank.
The counterattack
On 9 September Kutrzeba attacked south across the Bzura3 into the flank of the 8th Army. The surprise blow drove German divisions back and took prisoners, and for a few days the German advance on Warsaw was thrown into confusion.
The Germans turn
The German command reacted by turning large forces, including armoured units of Walter von Reichenau's 10th Army, back from the Warsaw front, while the Luftwaffe attacked the Polish columns and river crossings relentlessly3. The Polish attack lost momentum and Kutrzeba tried to break east toward Warsaw.
Encirclement
Squeezed into a shrinking pocket along the Bzura and under constant air attack, the Polish armies broke up. Some units fought their way through the Kampinos Forest to Warsaw and Modlin3, but most of the troops were killed or captured by around 22 September.
Why the Bzura mattered
The Bzura was the largest battle of the September Campaign and the only major Polish counteroffensive4. It cost the Germans time and casualties and helped Warsaw prepare its defence3, but it could not change the outcome, especially after the Soviet invasion of eastern Poland on 17 September4. It is remembered as the moment the Polish army struck back with everything it had.