Battle of the Bzura The Battle of the Bzura ( or Kutno or Battle of Kutno — German name ) was a battle in the opening campaign of World War II during the 1939 German invasion of Poland , fought between 9 and 19 September , 1939 , between Polish and German forces . Finally , the Germans outflanked the Polish forces and took all of western Poland . It was the single largest battle in the 1939 September campaign and took place to the west of Warsaw , near the Bzura River . In it , a Polish breakout attack gained initial success but eventually faltered after a concentrated German counterattack . Background . The Polish plan for defense against the German invasion , Plan West , called for the defense of the borders . This was dictated more by political than military concerns , as Poles feared that the Germans , after taking over territories they lost in the Treaty of Versailles , would try to end the war and keep those territories . While defending the borders was more risky , the Poles were counting on the British and French counteroffensive ( which never came ) . Due to this , Army Pomorze under general Władysław Bortnowski found itself in the Polish Corridor , surrounded by German forces on two fronts , and Army Poznań under general Tadeusz Kutrzeba was pushed to the westernmost fringes of the Second Polish Republic , separated both from its primary defensive positions , and from other Polish Armies . The German offensive proved the folly of the border defense plan in the first days of the war . Army Pomorze was defeated in the battle of Bory Tucholskie , and forced to retreat towards the south - east . Army Poznań , meanwhile , although not facing heavy German assaults , was forced to retreat east due to defeats of its neighbours ( Army Pomorze in the north and Army Łódź in the south ) ; both of them were retreating , meaning that Army Poznań was in danger of being flanked and surrounded by the German forces . On 4 September , Army Poznań moved through the city it was named after , Poznań , and abandoned it to the enemy , even through at this point it was not in contact with any significant German forces . By 6 September , Armies Pomorze and Poznań had linked up , forming the strongest Polish operational unit in the campaign , and general Bortkowski accepted the command of general Kutrzeba . On 7 September , Polish forces became aware of the German push towards Łęczyca , which if successful could cut off the retreat route of Polish forces . By 8 September , advanced German troops reached Warsaw , marking the beginning of the siege of the Polish capital . At the same time , German forces had lost contact with Army Poznań , and German command assumed that the army must have been transported by rail to aid Warsaw ' s defense ; they were unaware that in fact Army Poznań had merged forces with Army Pomorze , which they considered , since its defeat at Bory Tucholskie , no longer a significant threat . On 8 September the Germans were certain that they had eliminated major Polish resistance west of Vistula and were preparing to cross it and engage the Polish forces on the other side . Meanwhile , general Kutrzeba and his staff officers had suspected , even before the German invasion , that it would be the neighbouring Armies that would bear the German attack , and had developed plans at an offensive towards the south , to relieve Army Łódź . In the first week of the campaign , those plans , however , were rejected by the Polish commander - in - chief , Marshal Edward Rydz - Śmigły . By 8 September Kutrzeba had lost contact with Rydz - Śmigły , who had relocated his command center from Warsaw to Brest ; due to these factors , Kutrzeba decided to go forward with his plan . His situation was dire , as German forces were close to surrounding his units : the German 8th Army had secured the southern bank of the Bzura river , and the German 4th Army had secured the northern bank of Vistula , from Włocławek to Wyszogród , and its elements were attacking the rear of the Armies Pomorze and Poznań from the direction of Inowrocław and crossing the Vistula river near Płock . Opposing forces . Polish forces consisted of Army Poznań and Army Pomorze . German forces included the 8th Army under Johannes Blaskowitz and 10th Army under Walther von Reichenau of Army Group South ( " Heeresgruppe Süd " ) , elements of the 4th Army under Günther von Kluge of the Army Group North ( " Heeresgruppe Nord " ) and air support ( Luftflotte 1 and Luftflotte 4 ) . The battle . The battle can be divided into 3 phases : On the night of 9 September , the Polish Poznań Army commenced a counterattack from the south of the Bzura river , its target being the German forces from the 8th Army advancing between Łęczyca and Łowicz , towards Stryków . The commander of Poznań Army , Tadeusz Kutrzeba noticed that the German 8th Army , commanded by general Johannes Blaskowitz , was weakly secured from the north by only the 30th Infantry Division stretched over a 30 kilometre defensive line while the rest of the army was advancing towards Warsaw . The main thrust of the Polish offensive were the units under general Edmund Knoll - Kownacki , known as the Knoll - Kownacki Operational Group ( Polish 14th , 17th , 25th and 26th Infantry Divisions ) . The right wing of the offensive , in the area Łęczyce , included the Podolska Cavalry Brigade under general Stanisław Grzmot - Skotnicki , and on the left , advancing from Łowicz to the area of Głowno , the Wielkopolska Cavalry Brigade under general Roman Abraham . These groups inflicted considerable losses on the German defenders from the 30th Infantry Division and the 24th Infantry Division , with some 1 , 500 German soldiers killed or wounded and an additional 3 , 000 lost as prisoners during the initial push . The cavalry brigades supplemented with TKS and TK - 3 reconnaissance tanks moved to threaten the flanks and rear of the advancing German units . The German forces were thrown back approximately 20 kilometres and the Poles recaptured several towns , including Łęczyca and Piątek , and the village of Góra Świętej Małgorzaty . On 10 September , the Polish 17th Infantry Division met the German 17th Infantry Division at Małachowicze . The following day Polish forces continued their attack , advancing on Modlna , Pludwiny , Osse and Głowno . Initially underestimating the Polish advance , the Germans decided on 11 September to redirect the main force of the German 10th Army , the German 4th Army , the reserves of the Army Group South , and aircraft from 4th Air Fleet towards the Bzura . These forces included the German 1st Panzer Division , German 4th Panzer Division and the newly formed SS Infantry regiment Leibstandarte Adolf Hitler . German air superiority had a significant impact , making it very costly and difficult for the Poles to move units during the day . The following day the Poles reached the line Stryków - Ozorków . That day General Tadeusz Kutrzeba learned that units of Army Łódź had retreated to the Modlin Fortress , and decided to stop the offensive , instead looking to try to break through Sochaczew and the Kampinos Forest to reach Warsaw . On the morning of 14 September , General Władysław Bortnowski ' s 26th and 16th Infantry Divisions crossed the Bzura near Łowicz . The Polish 4th Infantry Division reached the road linking Łowicz with Głowno . At this point however , Bortnowski ordered the 26th Infantry Division to retreat . He had learned of the withdrawal of the German 4th Panzer Division from the outskirts of Warsaw , and was concerned that this Panzer division posed a threat to his men . On 15 and 16 September , Army Pomorze took up defensive positions on the northern bank of the Bzura . General Stanisław Grzmot - Skotnicki ' s group was located between Kutno and Żychlin , General Michał Karaszewicz - Tokarzewski ' s units near Gąbin , and parts of Army Poznań by the Bzura near Sochaczew , were ready to commence their drive towards Warsaw . To encircle and destroy the Polish forces , the Germans engaged most of their own 10th Army , including two armoured , one motorized , and three light divisions , equipped with some 800 tanks altogether . The attack from all sides on Polish positions started on 16 September , with the support of the Luftwaffe . On 15 September Poles were forced out of Sochaczew , a town on the Bzura river , and trapped in a triangle of Bzura , Vistula and German forces . The German 1st Panzer Division , after crossing the Bzura between Sochaczew and Brochów and engaging the Polish 25th Infantry Division managed to capture Ruszki , but its advance was then halted . Poles began to cross Bzura near Vistula , north of Sochaczew , and retreat towards Warsaw . Polish forces were forced to abandon most of their heavy equipment while crossing the river . On 17 September , German heavy artillery was shelling the crossing north of Brochów , and the largest air operation of the campaign began , with the Luftwaffe attacking the retreating Polish forces . During the night of 17 September , the main forces of Army Poznań attacked the German forces in order to break out of the German encirclement between Witkowice and Sochaczew . The 15th Infantry Division and Podolska Cavalry Brigade again crossed the Bzura in Witkowice . In Brochow , the 25th and 17th Infantry Divisions crossed the Bzura river . The 14th Infantry Division was concentrated in Łaziska . At the same time , Army Pomorze marched towards the villages of Osmolin , Kierozia and Osiek . In the morning the Germans started their drive towards the south along both banks of the Bzura , supported by more than 300 aircraft and heavy artillery . German howitzer s , taking advantage of their position on the high ground of the Vistula ' s right bank , shelled Polish positions for the entire day . And after two days of heavy fighting , with no ammunition or food rations remaining , further attempts at a breakout for the Poles became impossible . Aftermath . Only a few Polish units managed to break out of the encirclement . These groups entered Warsaw and Modlin , mostly around 19 and 20 September , crossing the Kampinos Forest , and fighting German units in the area ( for example , in the battle of Wólka Węglowa ) . Among them were Generals Kutrzeba , Knoll - Kowacki and Tokarzewski , two cavalry brigades ( Wielkopolska and Podolska ) of General Abraham , and the 15th and 25th Infantry Divisions . The remainder ( 4th , 14th , 17th , 26th and 27th Infantry Divisions ) , which didn ' t manage to cross the river , with General Bortnowski , capitulated between 18 and 22 September . Polish casualties were estimated at 20 , 000 dead , including three generals : Franciszek Wład , Stanisław Grzmot - Skotnicki and Mikołaj Bołtuć . German casualties are estimated at 8 , 000 dead . After the battle the remaining German divisions rushed towards Warsaw and Modlin and soon encircled both . The Bzura campaign ended in defeat for the Poles but because of the initial Polish local successes the German advance on Warsaw was halted for several days . The Wehrmacht was required to divert units from its push towards Warsaw . This enabled the Polish units defending Warsaw and its environs to better organize their own long - term , but ultimately failed , defense of the capital . The campaign also showed the importance of taking initiative , proved that horse cavalry units were still an important factor on the battlefield , and proved the importance of air superiority as well as confirmed that simple numerical superiority did still matter .