From 1 to 3 September 1939, on the fortifications north of Mława, the Modlin Army defended the shortest route from East Prussia to Warsaw against the German 3rd Army. For three days the 20th Infantry Division beat off attacks by infantry, tanks and aircraft and did not yield the Mława position to frontal assault. The Germans, however, broke through the front at Rzęgnowo, and on the night of 3–4 September the army commander ordered a retreat.