At the same time, an assault on the southern part of Polish fortifications became a stalemate. The Polish bunkers lacked adequate anti-tank armament, but were able to rake the German infantry with machine gun fire. However, at 6 o'clock in the evening, the Polish infantry was forced to abandon the trenches and field fortifications and retreat into the bunkers. The German tanks could finally cross the Polish lines and advance towards Tykocin and Zambrów. However, the German infantry was still under heavy fire and was pinned down in the swampy fields in front of the Polish bunkers.