The evacuation of large elements of the British and French armies from Dunkirk (wiki) on the French coast, which took place during the period from May 26 through June 4, 1940, followed their defeat by the German blitzkrieg that overwhelmed France during the early months of World War II. The sudden German attack through Belgium on May 10 had quickly rolled up the French and British left wing and surrounded it in a small enclave on the English Channel opposite Dover.
In a largely improvised but brilliantly executed maritime operation that mustered both the Royal Navy and civilian small craft of every kind, nearly 340,000 British and French troops - nearly 90 percent of those invested - were ultimately withdrawn, despite incessant German armored and air attacks.
Dunkirk was, of course, the inspiration for Winston Churchill's "We shall fight on the beaches...we shall never surrender" speech:
We shall not flag or fail. We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing in the air, we shall defend our island, whatever the cost may be, we shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender.
More on Dunkirk here, including a contemporaneous newsreel.