At this moment Adolf Hitler was in a position to deliver such a devastating military defeat to the British that they might never have recovered. But Hitler hesitated. His panzer corps – fast-moving tank-led army divisions – had ripped through the defenses of France and Belgium and had trapped the British in a shrinking enclave around the French port of Dunkirk.

But then, on May 22, the panzers were halted by orders from above, and again on May 23. Just why this happened, and on whose orders, has been disputed for decades by historians.

What is not disputed is that if the panzers had been allowed to roll onward during those two days they could have driven the opposing British and French forces into the sea. Instead, the allied forces gained just enough time to be evacuated from the beaches of Dunkirk in the epic action now graphically recreated in Christopher Nolan’s movie, Dunkirk.