Polish 20th Infantry Division

20th Infantry Division (Polish: 20. Dywizja Piechoty) was a unit of the Polish Army during the interbellum period, which took part in the Polish September Campaign. It was formed in 1920 from the reorganization of the 2nd Lithuanian-Belarusian Division. Stationed in Baranowicze and commanded by Colonel Wilhelm Andrzej Lawicz-Liszka.

September 1939 Campaign

In the summer of 1939 it was moved west and became part of the Army Modlin. Its task was to defend the partly fortified area north of Mława, near the inter war border of Poland and East Prussia.

Between September 1 and 3, 1939 (see: Polish September Campaign), the Division defended positions around Mława (see: Battle of Mława), facing the more numerous and better equipped units of the German 1st Army Corps (composed of: 11th Infantry Division, 61st Infantry Division and the Panzer Division Kempf).

The Wehrmacht was advancing southwards, towards Warsaw, but first attacks were repulsed with the loss of around 25 German tanks. Unable to capture Mława in frontal attack, the Germans decided to go around and attack from sides. As they threatened 20th I.D.'s rear, the Poles were ordered to withdraw. However, supported by the neighbouring Polish 8th Infantry Division, the defenders kept their positions.

On September 2, German attacks failed again, even though they ordered Polish civilians to walk in front of their tanks. The Germans decided to organize an offensive from the area of Ostrołęka and Przasnysz. This succeeded, and on September 3, Polish positions were broken. To make matters worse, the counter-attack of the 8th I.D. was ill-organized and failed, resulting in chaotic, panic withdrawal of 8th I.D. units.

...
Wikipedia