 A series of Allied counter-attacks—including the Battle of Arras—failed to sever the German spearhead, which reached the coast on 20 May, separating the BEF near Armentières, the French First Army, and the Belgian Army further to the north from the majority of French troops south of the German penetration.After reaching the Channel, the German forces swung north along the coast, threatening to capture the ports and trap the British and French before they could evacuate to Britain.In one of the most debated decisions of the war, the Germans halted their advance on Dunkirk.