Dunkirk is the battlefield where the Germans made their first big mistake in World War II.  General Guderian, General Rommel, and other German generals were in the process of obliterating the Allied forces in France and Guderian's Panzer divisions were poised to apply the coup de grace to the surviving British (along with some French and other nationalities)  army forces trapped at Dunkirk.  About 300,000 Allied troops were virtually defenseless and nervously awaited a hastily-assembled flotilla of  naval and amateur craft sent to fetch them back to England.  Unaccountably, Hitler ordered  Guderian's  Panzers to halt, giving the British time to board their vessels and return to England.  When the British troops arrived in England, they were without arms as they had to abandon their weapons at Dunkirk.  Still, they were home and, eventually, would be rearmed and ready for action.  These troops were the elite of the British army.

The Germans needed to destroy the British forces at Dunkirk, an action that would have likely forced the English to drop out of the war.  Some experts have suspected that Hitler, who had no great dislike for the British (as he did the French, Russians, etc), deliberately allowed the British to escape thinking that Churchill would sue for peace, anyway.  If these were his thoughts, he badly misjudged Churchill who was as tough as they come.

 Most would be satisfied with just walking the Dunkirk beach where the desperate young British soldiers stood in long lines hoping to board the next available vessel.  The strain on the waiting soldiers waiting on that beach battlefield must to have been horrendous.