Dunkirk was the evacuation of the British Expeditionary Force after they had been pushed back to the European coast. The small proffesional army weren't prepared for the modern 'Blitzkrieg' tactics of the German Forces. The BEF where the strongest force that faced the German onslaught in france but with the southern flank (Dam Frogs!) retreating, the out numbered British had been reduced to a series of holding actions under the mercy complete German air superiority.
Despite being a military defeat in every sense, the way that the British small boat owners and the Royal Navy sailed across to Dunkirk, and made every effort to evacuate as many of the British and French forces as possible, stood out during the next few years as a signal for defiance and solidarity. No matter how close the British people got to being defeated, they never lost that 'Dunkirk Spirit'.
Short story about LostBoss's Grandad.
Now here's a story, my Grandad was at Dunkirk (a dashing young signaller) and obviously wasn't having a great time. So Grandad is chest deep in water struggling to get to one of the boats when he feels a hand on his shoulder. "Do you need a hand there our kid?" says his brother - who he hasn't seen in over a year.
Small world and all that, so Grandad gets off the beach and spends the war with the 8th Army. Nice one Grandad.