On 10 May 1940, Germany invaded France and the Low Countries, pushing the British Expeditionary Force (BEF), along with French and Belgian troops, back to the French port of Dunkirk. A huge rescue, Operation 'Dynamo', was organised by the Royal Navy to get the troops off the beaches and back to Britain.
Admiral Bertram Ramsay directed the evacuation. Ramsay had retired before the war but was recalled in 1939. He and his staff worked in a room deep in the Dover cliffs that had once contained a dynamo, a type of electrical generator, giving the operation its name.
'Dynamo' began on 26 May. Strong defences were established around Dunkirk, and the Royal Air Force sent all available aircraft to protect the evacuation. Over 800 naval vessels of all shapes and sizes helped to transport troops across the English Channel. The last British troops were evacuated on 3 June, with French forces covering their escape. Churchill and his advisers had expected that it would be possible to rescue only 20,000 to 30,000 men, but in all 338,000 troops, a third of them French, were rescued. Ninety thousand remained to be taken prisoner and the BEF left behind the bulk of its tanks and heavy guns. All resistance in Dunkirk ended at 9.30am on 4 June.
If the BEF had been captured, it would have meant the loss of Britain's only trained troops and the collapse of the Allied cause. The successful evacuation was a great boost to civilian morale in Britain, and created the 'Dunkirk spirit' which helped the country to fight on.