The British and French troops trapped at Dunkirk prepared to evacuate behind whatever thin defensive lines they could muster. But the panzer divisions facing them had outrun their own supply echelon and been exhausted by constant combat. They could not hope to strike the final blow. The Germans therefore released 1st Panzer Division from its mission reducing the defenses around Calais and sent it eastward toward the canalized Aa River. At St-Nicolas and La Bistade (south of Gravelines), a collection of cavalry, infantry and old anti-aircraft trucks defended the bridges across the canal, but not any other locations. Infantry Regiment Grossdeutschland (attached to 1st Panzer Division) would establish and consolidate a bridgehead on the Aa River. The first firefights erupted the night before Hitler ordered a halt to the German attack on Dunkirk.

At dawn, the Germans attacked all along the canal line, which presented the last major obstacle before Dunkirk itself. Some Germans attacked the bridges while others crossed the canal in small boats and hit the French in the flanks near St-Nicolas and La Bistade. The bridges’ defenders had no reserves to call on, but their mortars and autocannon slowed the Germans enough to allow for an orderly retreat despite heavy losses.