Although not under von Bock's command, Kesselring's purpose was to support Army Group North in closing the Polish Corridor from the third day, with emphasis thereafter on supporting the 3rd Army as it advanced along the Vistula to isolate Warsaw from the east. From 8 September Kesselring began interdiction operations against bridges as German forces advanced on Warsaw. When a powerful Polish counter-attack created a crisis, he contributed "Fliegerdivision 1" to the Battle of the Bzura. The division contained 70 per cent of his dive-bombers and was assigned to Löhr on 6 September. The air attacks assisted in the destruction of two Polish armies.