Retreat to Dunkerque
With the collapse of these measures, the forces in the pocket appeared doomed. Boulogne was about to fall, and Calais was under siege, leaving Dunkerque as_ the only port. German armor had already forced one crossing of the canal line, and a rapid thrust to cut the Allied troops from the sea seemed likely. Then, abruptly, the German armor came to a halt. In later years some German commanders tried to place full responsibility for the decision to halt the armor on Hitler, but contemporary records appear to indicate that even if the decision was Hitler’s, the impetus for it came from Rundstedt. By May 23, Rundstedt’s tanks had incurred 50 percent losses, and the terrain beyond the canal line, crisscrossed by waterways and flooded lowlands, was unattractive for armor. Furthermore, heavy tank losses at this stage would seriously endanger the pending attack southward across the Somme into the heart of France. In the early evening of May 23, Rundstedt ordered his armor to halt, ostensibly to reorganize before moving against the canal line. The next morning, however, after a conference with Rundstedt, Hitler sanctioned stopping the armor altogether and leaving the mopping up to the infantry divisions.
At almost the same moment a new threat developed from another direction against the forces in the pocket. On either side of Kortrijk (Courtrai) on the Lys River, Bock’s Army Group B opened a major attack against the Belgians. Despite help rushed by the British and the French, the Belgian Army began to give way on May 26. Concluding that his forces were too depleted and embattled to break away for withdrawal to the Yser River, King Leopold on the next day sent an emissary to the Germans to ask the terms of an armistice. Though the terms were unconditional surrender, he deemed that he had no choice but to accept, and the army surrendered on May 28. Anticipating the Belgian collapse, the British government, in the early evening of May 26, had authorized Lord Gort to withdraw the BEF to England. The French Command authorized one of three French corps to participate in the withdrawal, but the other two corps of 6 divisions, closely engaged near Lille, fought on until they were surrounded, eventually surrendering on June 1.
The withdrawal to a shallow perimeter based on canal and river lines around Dunkerque began the night of May 27 and continued through the next day. The embarkation maneuver, called Operation Dynamo, began officially on May 27. A disappointing 7,669 men were embarked that day, but the tempo of the operation picked up thereafter. A total of 848 British, Dutch, Belgian, and French ships of all sizes from destroyers and Channel ferries to fishing smacks and private yachts plied the rough waters of the Channel under the cannon and bombs of the Luftwaffe and the guns of coastal batteries for eight days and nights. They removed from the harbor of Dunkerque and nearby beaches 338,226 men, two thirds of them British.