Dunkerque is a French city spelled Dunkirk in English.
After the surrender of Belgium, French and British forces in Belgium retreated to Dunkirk, on the northern coast of France. Here they held off the Germans while more than 300,000 Allied troops waded out to British rescue-vessels in late May 1940. The tiny British Royal Air Force formed aerial umbrella to hold off the German bombers.
The successful operation saved the entire British army. If the Dunkirk rescue had failed, the British troops would certainly have been defeated or captured. However, as British Prime Minister Winston Churchill noted afterward, "Wars are not won by evacuations."