The Battle of Modlin took place during the German invasion of Poland at the beginning of the Second World War. Modlin Fortress was initially the headquarters of the Modlin Army until its retreat eastwards. From 13 September to 29 September in 1939 it served as a defensive citadel for Polish forces under the command of General Wiktor Thommée against assaulting German units. This fighting was closely linked with the strategic situation of the Battle of Warsaw.
The Polish forces defending the fortress included the armoured train 'Śmierć' (death), and the Modlin anti-aircraft battery was credited with shooting down more Luftwaffe planes than any other in the entire September campaign.
Fortress Modlin capitulated on 29 September, one of the last to lay down its arms in the campaign.