As the Allied Dyle-Breda Plan collapsed under the pressure of the Wehrmacht’s Blitzkrieg, most of the British Expeditionary Force of more than 320,000 men fell back against the French coast around Calais and Dunkirk. Germany’s Fall Gelb (Case Yellow) had been radically modified in early 1940 from a plan looking nearly identical to that of 1914, to one which included a decisive armored thrust through the Ardennes Forest that would break the Allied armies in two and trap the preponderance of Allied combat power in a pocket north of Paris. The Blitzkrieg which began in 10 May 1940 had shattered the Dutch, Belgian, and French armies.
The Wehrmacht employment of auftragstaktik allowed German commanders at all levels to consistently defeat Allied tempo of decision-making, which led to countless occasions where German units slammed into French and British formations who were de-training or still in road march formation and unready for battle. Speed, both in tactical mobility and command and control, was as decisive as any other single factor in the Battle of France.
Sixteen days into office, Prime Minister Winston Churchill had known since 15 May that the French were finished. Despite attempts to reinforce his French allies, by 21 May the objective of the BEF was to conduct a fighting withdrawal to a Channel port, from where it might, if extremely fortunate and able to gain local air superiority, be evacuated back to Britain.
Operation DYNAMO, which would include a massive commitment of the Royal Navy, the Royal Air Force, and thousands of small ships and craft, began on 26 May 1940. With two French divisions holding against German pressure, British units began to move toward the beaches and piers, the ships and craft (in the surf line) which would shuttle them both to larger ships and to England itself. That German pressure was not nearly as heavy as it might have been, thankfully for the British. Reichsmarshall Goering had promised Hitler that his Luftwaffe would destroy the Allied evacuation efforts without having to risk von Küchler’s Panzer and Panzergrenadier units in coastal sand unsuitable for their deployment.
In the end, German commanders convinced Hitler to launch concerted attacks on Dunkirk, but it would come too late. Dunkirk was finally captured on 4 June 1940, but by that time, 198,000 British and 123,000 French troops had been evacuated. The RAF had paid a heavy price for the furious defense of the skies over Operation DYNAMO, losing 177 precious fighter aircraft that had been jealously hoarded for the battle over the skies of England that was sure to come. The Royal Navy lost six modern destroyers, and several hundred small craft. Virtually all of the BEF’s heavy equipment, tanks and trucks, artillery pieces, and more than 70,000 tons of ammunition was left on the beach. And nearly 15% of the BEF’s soldiers were dead, wounded, or prisoner.
But the vast preponderance of British manpower had been saved. German intelligence reports in preparation for SEELÖWE noted the toughness and high quality of the British Soldiers, including the Territorials. Most of them were back safely on British soil, and the Wehrmacht would have to deal with them in the near future under far less favorable circumstances. Those plucked from the Dunkirk docks and surf included the British Commander of II Corps, Lieutenant General Sir Alan Brooke, later Chief of the Imperial General Staff, and Major General Bernard Law Montgomery, in command of the 3rd Infantry Division. Dunkirk had been a miracle indeed. And the Germans would pay dearly for their mistake.
Churchill’s admonition that “wars are not won by evacuations” not withstanding, the successful evacuation of the bulk of the BEF from Dunkirk allowed England to survive until the Soviet Union and the United States entered the war. Lost on the 73 years since the evacuation of Dunkirk was the fact that there was a considerable body of opinion in Parliament that desired a negotiated peace with Germany. With the loss of the BEF, such a body of opinion might have been strong enough to have blocked Churchill’s desires to fight Hitler to the bitter end. DYNAMO signaled what Churchill told the British people, that “the Battle of France is over, the Battle of Britain is about to begin”. Defending the Island Nation was the force evacuated from France.