The siege of Dunkirk in World War II (also known as the Second Battle of Dunkirk) began in September 1944, when Allied units of the Second Canadian Division surrounded the fortified city and port of Dunkirk. The siege lasted until after the official end of the war in Europe. German units within the fortress withstood probing attacks and as the opening of the port of Antwerp was more important, the 21st Army Group commander, Field Marshal Bernard Montgomery, decided to contain but not capture Dunkirk with the 1st Czechoslovak Armoured Brigade. The fortress, commanded by Admiral Friedrich Frisius, eventually surrendered unconditionally to Brigadier General Alois Liška, the commander of the Czechoslovak brigade group, on 9 May 1945, a day after the surrender of Nazi Germany took effect.