- Theatre: France
- Dates: 26 May to 4 June 1940
- Location: Dunkirk
- Outcome: Operation Dynamo, the evacuation of around 350,000 British, French and Belgian troops from Dunkirk, enabled the Allies to continue the war and was a major boost to British morale.
- Britain: Viscount Gort's British Expeditionary Force (BEF) comprising 13 infantry divisions
- Germany: 19th Panzer Corps, under General Heinz Guderian; 41st Panzer Corps, led by General GH Reinhardt
As France fell rapidly, the Allies' northern and southern forces were separated by the German advance from the Ardennes to the Somme. The Allied armies in the north were being encircled.
By 19 May 1940 the British commander, Viscount Gort, was considering the withdrawal of the British Expeditionary Force (BEF) by sea. But London was demanding more action and on 21 May, Gort launched an attack from Arras.
This attack lacked the necessary armour and General Heinz Guderian's tanks continued past Boulogne and Calais to cross the canal defence line close to Dunkirk, the only port left for an Allied withdrawal from Europe.
On 24 May, just as Guderian was expecting to drive into Dunkirk, Hitler gave the surprise order to withdraw back to the canal line. Why the order was given has never been explained fully.
One possible explanation is that Reichsmarschall Hermann Göring, head of the Luftwaffe, assured Hitler that his aircraft alone could destroy the Allied troops trapped on the beaches at Dunkirk. Others believe Hitler felt that Britain might accept peace terms more readily without a humiliating surrender. Whatever the reason, the German halt gave the Allies an unexpected opportunity to evacuate their troops.
Evacuation began on 26 May and gained urgency the next day, when Field Marshal Walter von Brauchitsch, the German Commander-in-Chief, persuaded Hitler to rescind his orders and German tanks again advanced on Dunkirk.
By this time the Allies had strengthened their defences and the tanks met heavy resistance. Almost immediately, Hitler ordered them instead to move south for the imminent attack on the Somme-Aisne line, another lucky break for the Allies.
Heavy German bombing had destroyed Dunkirk's harbour, and there were hundreds of thousands of men on the beach, hoping to be rescued. The Luftwaffe attacked whenever the weather allowed, reducing the town of Dunkirk to rubble.
On 29 May, the evacuation was announced to the British public, and many privately owned boats started arriving at Dunkirk to ferry the troops to safety. This flotilla of small vessels famously became known as the 'Little Ships'. The contribution these civilian vessels made to the Dunkirk evacuation gave rise to the term 'Dunkirk spirit', an expression still used to describe the British ability to rally together in the face of adversity.
By 4 June, when the operation ended, 198,000 British and 140,000 French and Belgian troops had been saved, but virtually all of their heavy equipment had been abandoned. Six destroyers had been sunk, along with eight personnel ships and around 200 small craft, from a total of around 860 vessels of all sizes.
A further 220,000 Allied troops were rescued by British ships from other French ports (Cherbourg, Saint-Malo, Brest, and Saint-Nazaire), bringing the total of Allied troops evacuated to 558,000.
Although the Germans had taken over a million Allied prisoners in three weeks at a cost of 60,000 casualties, the evacuation was a major boost to British morale and enabled the Allies to fight another day - even if that fight was to be on home turf, resisting the expected German invasion of Britain.