Andreas Whittam Smith: The lessons May 1940 has for today

During the astonishing political events that have taken place since the general election on 6 May, my mind has often turned to an even more remarkable month of May in British history, May 1940. We have been so absorbed by the construction of Britain's first coalition government since the Second World War that we haven't paused to recall the extraordinary circumstances in which its predecessor came into being. A whole series of 70th anniversary dates has passed by unnoticed. Only the evacuation of Dunkirk still catches the imagination.

Yet the month of May 1940 poses a great question for which no totally convincing explanation has ever been found: why was France, a super-power with an extensive empire and well-equipped armed forces, defeated within a matter of weeks, leaving Britain alone to face Hitler's Germany?

Winston Churchill succeeded Neville Chamberlain as Prime Minister on 10 May 1940. He immediately sent a message to Clement Attlee, the leader of the Labour Party, the official opposition, asking him to join the new Government. Attlee agreed and Churchill then mentioned four of Attlee's colleagues – "men whose service in high office were immediately required".

On that same day Germany invaded Holland and Belgium. Thus the phoney war ended and the real war began on the same day that Churchill entered Downing Street – as if waiting for him. Until then, Hitler had made no move against the West since his troops had invaded Poland on 3 September 1939 and Britain and France had immediately declared war on him without being able to do a thing about Poland, which was quickly overrun.

One way of comprehending the sheer speed of events in May 1940 is to lay recent dates over them: 10 May 2010 was the Monday morning following the recent election. By 13 May, David Cameron and Nick Clegg had laid out their coalition pact. It was on 13 May 1940 that German armed columns unexpectedly crossed the French border near Sedan.

By 25 May, German troops had reached Calais and were to encircle the British Expeditionary Force at Dunkirk soon afterwards. This week, the 25 May was the day of the Queen's Speech. On the day you are reading this 70 years ago, the evacuation of Dunkirk was under way and was completed on 4 June. By the 14 June 1940, the Germans had occupied Paris; two days later France capitulated. On 18 June, Churchill spoke to the House of Commons about these terrible events, concluding with an oft-quoted peroration: "Let us therefore brace ourselves to our duty and so bear ourselves that if the British Empire and its Commonwealth lasts for a thousand years men will still say: 'this was their finest hour'."

Marshal Pétain, who ruled France during the German occupation and was afterwards convicted of treason, explained the defeat as having been caused by "insufficient recruits, insufficient equipment, and insufficient allies". When the war began, France and Britain had 4,200 tanks on the Western Front, 4,500 military aircraft and 76 army divisions in place. After the war, the German archives showed that Germany had had 4,400 tanks, 3,500 aircraft and 80 divisions. The strength of the two sides had been broadly the same.

Later, Pétain's government, based at Vichy in the unoccupied zone of central France, put the blame on the state of France itself. The defeat was variously attributed to materialism, alcoholism, a low birthrate, dechristianisation and the break-up of family. The regime that so faithfully applied Nazi policies wanted to show that it was morally superior to what had gone before. Yet France had been impressively governed in the final years of the 1930s. Rearmament had gone on apace and a general strike quickly petered out. The country was getting itself together when its armed forces suddenly crumbled in face of the German advance.

The spotlight must therefore be directed at the French High Command itself. Did it fail to learn the lessons of Hitler's rapid conquest of Poland in the autumn of 1939 when it had time to do so? French generals carefully studied Hitler's success but then concluded it was no precedent. The French border with Germany was shorter and better guarded than the Polish border. The Poles had had no time to prepare. Even so they had inflicted heavy damage on Germany's armoured divisions. The German success wouldn't be repeated.

Besides, the French General Staff had already done a great amount of scenario testing and planning during the 1920s and 1930s. One historian notes that conscientious, patriotic and often remarkably intelligent staff officers had spent innumerable hours trying to determine which policies would work best on the battlefield. "The French commanders didn't fall victim to their own stupidity, decadence, disloyalty or defeatism. They failed because they placed excessive confidence in logic and reason." Unlike some of the German generals leading the Panzer divisions into France, they couldn't, as today's phrase has it, "think out of the box".

In the event, the Germans appeared where they were least expected. They came through the Ardennes, a thickly wooded and hilly region that was very difficult for the swift passage of troops. They rapidly approached the River Meuse at Sedan. Almost immediately, on 13 May, a French artillery observer claimed that German tanks had crossed the river. The news spread quickly and caused panic in the French lines. Many soldiers believed they had seen them. Units quickly became confused and disorganised.

Yet after the war it was established that the German tanks didn't cross the Meuse until 12 hours later. The French army had fallen prey to what a Commission of Enquiry referred to as a "collective hallucination". Then, the breakthrough having been achieved, the German commanders ignored their superiors' reservations and drove towards the Channel as fast as they could. Churchill went to Paris on 16 May. The next day, having returned to London, he informed the war cabinet that a total French defeat was imminent.

There is a moral here. One is often surrounded by conventionally minded, sensible, even intelligent people who seldom make mistakes – the French High Command in this case. Yet in certain circumstances, chiefly because of a failure of imagination and sometimes of nerve, these same people are completely useless. Therein lies, I believe, the key to understanding the turbulent events of May 1940.

a.whittamsmith@independent.co.uk