Why, in 1940, did Christopher Nolan have to come to the rescue of 340,000 Allied troops on a beach in northern France? Or, to put it with less snark, why had the Allies (principally, France) performed so badly that, less than a month into the German invasion, they found themselves cornered against the sea?
"Thank God for the French Army," said Winston Churchill in 1933; and as late as 1940, France was seen as Europe's preeminent military power. Twenty years before it had repelled an invasion by a country a third larger in population and twice as large in industry, at the human cost of 4 percent (!!) of its citizenry. For two decades it had prepared for invasion, building forts and husbanding its strength, such that in 1940 the French army had more guns than the Germans, and more tanks. And still it lost. Why?
Robert Doughty (a retired US brigadier) points the finger at the Battle of Sedan. With the infamous Maginot Line defending the Franco-German border, the Allies had sent their best units north into central Belgium, anticipating a strike along the same lines as the German invasion of 1914. But they had dismissed the possibility that the enemy might try something different. The Germans launched a feint through central Belgium, to confirm Allied preconceptions; but the real attack came through the Ardennes forest, the critical hinge between the mobile Allied units in the north and the Maginot Line in the south. That area (which included the town of Sedan) was lightly defended, on account of it being deemed poor terrain for tanks; and through a combination of bad luck, French incompetence, and German derring-do, the Germans broke through. In five days, German tanks were at the sea, and the fate of the main Allied army was sealed.
All that said, this isn't a great book. Only the most ardent grognard could get past the awkward writing and the fussy preoccupation with military detail -- with so few maps, the many pages of after-action description feel flighty, weightless. I found myself flipping through these sections. But the two chapters on strategic concerns are quite good, and neatly summarize the key reasons why Sedan was allowed to happen.
The French in 1940 were preoccupied with the idea of "methodical battle": a top-down, centralized approach to warfare. Artillery was responsible for most of the battlefield casualties in First World War, and the difficulties of coordinating massed firepower lent itself to a top-down approach to command. With 1.3m French soldiers killed in La Grande Guerre, an attachment to the ideas had won the last war is understandable. But faced with a new German doctrine that emphasized mobility and seizing the initiative, this doctrine was a disaster. This book could be flippantly subtitled Leadership Secrets of the Wehrmacht: French units at Sedan were repeatedly outmaneuvered and outfought by fast-moving German units, led by junior commanders who knew how to seize the initiative. But Doughty is careful not to descend into the German weeabooism. The German victories at Sedan were won primarily by infantry, not by tanks; "Blitzkrieg" was not a codified doctrine, but an ex-post invention of the Allied press to describe the rapid string of German victories; and there was a great deal of bad luck on the Allied side that made collapse possible.
I left this book with a sense of just how contingent history can be. There was nothing inevitable about France's defeat in 1940; all claims about moral decay or French cowardice are hogwash. France had the materiel and the will to win. What it lacked was the correct ideas about how to wage war, and it was unfortunate enough to be paired with adversary with new ideas that countered the old ones. If France had stood in 1940, 70,000 French Jews might have lived. More than that, facing a determined enemy to its west, Germany might not have invaded the Soviet Union, and Eastern Europe might have been spared the horrors of the Eastern Front, including the Holocaust. Military matters matter. Sedan was not just the hinge of the French Army; it was at the hinge of history. Had things swung differently, the world might be a happier place.