The Battle of the Bzura (or the Battle of Kutno) was the largest Polish counter-attack of the German invasion of Poland and was fought from 9 to 19 September. The battle took place west of Warsaw, near the Bzura River. It began as a Polish counter-offensive, which gained initial success, but the Germans outflanked the Polish forces with a concentrated counter-attack. That weakened Polish forces and the Poznań and Pomorze Armies were destroyed. Western Poland was now under German occupation. The battle has been described as "the bloodiest and most bitter battle of the entire Polish campaign". Winston Churchill called the battle an "ever-glorious struggle". Background The Polish plan to defend from the German invasion, Plan West, called to defend the borders. That was dictated more by political than military concerns, as Poles feared that the Germans, after they had taken over the territories that they had lost by the Treaty of Versailles, would try to end the war by keeping those territories. Defending the borders was risky, but the Poles were counting on a British and French counteroffensive, (which never came). That made Army Pomorze, under General Władysław Bortnowski, find itself in the Polish Corridor while it was surrounded by German forces on two fronts. Army Poznań, under General Tadeusz Kutrzeba, was pushed to the westernmost fringes of Poland and was separated from its primary defensive positions and from other Polish Armies. The German offensive proved the folly of the Polish border defence plan during the first days of the war. Army Pomorze was defeated at the Battle of Bory Tucholskie and was forced to retreat to the south-east. Army Poznań, meanwhile, did not face heavy German assaults but was forced to retreat to the east by defeats of its neighbours (Army Pomorze in the north and Army Łódź in the south). Both of them were retreating and so Army Poznań was in danger of being flanked and surrounded by the German forces. On 4 September, Army Poznań moved through Poznań and abandoned it to the enemy although at that point, it was not in contact with any significant German forces. By 6 September, Armies Pomorze and Poznań had linked and formed the strongest Polish operational unit in the campaign, and General Bortnowski accepted the command of General Kutrzeba. On 7 September, the Polish forces became aware of the German push towards Łęczyca, which, if successful, could cut off