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.