The brigade was then moved up to support the Allied Siege of Dunkirk. 149 LAA deployed outside the perimeter on 17 September. The brigade acted both as an AA defence formation and as an Army Group Royal Artillery, with both HAA and LAA guns being employed against ground targets, beginning the day after their arrival and lasting until February 1945. The two LAA regiments (149 and 32) were sometimes firing 5-6000 rounds a day of 40mm ammunition. In October the "Luftwaffe" began low-level air drops of supplies to the beleaguered German garrison, and these were targeted by LAA guns working in cooperation with searchlights. By December, 502 Bty had been detached from 149 LAA Rgt and was deployed under 74th AA Bde to guard the vital bridges at Nijmegen, Grave and Mook. Large numbers of German aircraft attacked or overflew these bridges in December during the Ardennes offensive, particularly on 1 January 1945 (Operation Bodenplatte).