The German army had breached French defenses at Sedan and turned to the English Channel. On May 20th they had reached the coast and threaten to cut off both the British Expeditionary Force in Belgium and the French troops fighting there. The Germans turned North after reaching the coast. The Allied forces were now battled up in an area with Dunkirk in the center. The German believed that the area around Dukirk was not suitable for tank forces and feared an allied break out. Thus the army requested and Hitler approved a halt to allow forces to regroup. The German army halted for three days, three days that were critical allowing the allies to organize a defensive perimeter around Dunkirk. By the time the Germans resumed their attack three das after halting it on May 23rd, the allies had strong lines in place and were able to temporarily hold back the German advance.
While the Germans were being held back at the perimeter the British had send every available sea worthy vessel to Dunkirk to embark their troops. From May 27th to one 4th despite repeated air attacks and artillery fire 338,228 men escaped including 139,997 French, Belgium and Polish troops. At total of 861 ships were used, of which 243 were sunk.