10 May – 17 June 1940

A squadron of Junkers Ju 87 ‘stuka’ dive-bombers in flight over Poland. The use of dive-bombers in the invasions of Poland and France was an important innovation in army support and one that neither the British nor French air forces had developed by 1940.

German victory over British, French, Belgian and Dutch forces in the Battle of France in May and June 1940 has often been seen as the inevitable result of heavy German rearmament in the 1930s compared to the late and insufficient preparation of the Allies. Yet on paper the balance between the two sides was much more even, while a large part of French territory was defended by a solid wall of fortifications, the Maginot Line. It is a commonplace that the attacker has to outnumber the defender by two or three to one to overcome the advantages of prepared defences. In the Battle of France this prescript was overturned. German forces demonstrated that it was battlefield innovation that mattered, not the balance of numbers.

The battle is best remembered for the triumphant display of what was widely called Blitzkrieg, or lightning war, although the German armed forces did not use the term themselves at the time. They focused on the first effective use of a combined arms offensive, making the most of modern tracked and armoured vehicles, principally tanks, mobile motorized infantry and battlefield air power – fighters, dive-bombers and medium bombers.

The roots of this lethal combination of striking power lay in the period immediately after the First World War when Germany was disarmed by the Treaty of Versailles. The German Defence Ministry set up a large number of study groups to learn the lessons of the previous conflict. Although they now had no tanks or military aircraft, the German armed forces worked out the effectiveness of enhanced mobility and aerial striking power as a battering ram to pierce the enemy front line and allow the mass of infantry to follow, encircling and annihilating the enemy. This was what they had wanted to do in 1914, but they had lacked the mobility and firepower. After six frantic years of rearmament, by the eve of the attack on 10 May 1940, German forces had mustered 2,439 tanks and 3,369 aircraft.

On paper, the Western Allies still outnumbered the Germans. With the addition of Dutch and Belgian forces, which were attacked at the start of the campaign to clear one of the avenues for the German approach, the Allies could count 4,204 tanks and 4,981 aircraft; they deployed 152 army divisions against the German 135. The difference between the two sides was the way those forces were exploited. Most of the British air forces were defending Britain or posted overseas; French aircraft were spread across metropolitan France protecting industrial zones or defending the French empire in North Africa. The British sent only 250 aircraft to northeastern France opposite the German line of attack, the French only 500. They faced 2,741 German aircraft concentrated in two air fleets to support the armies on the ground. French tanks were spread throughout their army units rather than concentrated in mobile armoured divisions, while some were posted to defend the Maginot Line of fixed fortifications.

Concentration of force was not the only strength of the German campaign. The ten armoured and motorized divisions carried with them mobile anti-aircraft batteries to defend them against enemy air attack. Battlefield anti-aircraft artillery was significant in destroying the slow-flying light bombers of the RAF expeditionary air force. The Germans also had an effective means of radio communication, which meant that army units on the ground could contact the supporting air fleet for immediate assistance from bombers and dive-bombers, whereas the British army had to send requests for help via London, which could take hours. The rate at which German aircraft operated was also critical. German fighters averaged four sorties a day, the French fighters less than one. German tanks were mainly light and underarmed, but the secret of combined arms operations was to bring the mobile infantry, artillery batteries and engineers together in one integrated body, capable of exploiting a breakthrough, where the British, who did have armoured units, concentrated too much on a preponderance of tanks at the expense of infantry and artillery.

The Battle of France was not a conventional battle lasting a day or two with a clear conclusion, but a series of operations that lasted six weeks, with regular large-scale fighting all along the line of German attack. Within five days the Dutch army surrendered; the Belgian army was pushed back rapidly until it met up with units of the British Expeditionary Force as it moved into Belgian territory, but Belgium surrendered on 28 May. German forces moved forward rapidly through the Low Countries, but this was not the main axis of attack. Large German mobile forces were concentrated in the region of the Ardennes Forest, north of the Maginot Line. Long considered impassable for modern armies, the Allies neglected the sector. The German plan was to use this area as the launch pad for a heavy armoured thrust at the French line to create panic and allow for the encirclement of much of the Allied front. On 13 May, the tanks of General von Kleist’s five armoured divisions rolled out of the forest; there had been long queues of vehicles and the rugged terrain and narrow roads made it difficult to manoeuvre. If the Allies had understood the threat and sent aircraft to bomb the vehicles, the outcome might have been different, but the air forces were too busy opposing the bulk of the German air force further north.

Once out in the open, the armoured divisions poured across the River Meuse, opening up a wide gap in the French front. Within six days German armour, continuously supported by bombers and dive-bombers, had reached the Channel coast at Abbeville, surrounding the British forces, the French 1st Army and the remnants of the Belgian divisions. The British could see that the battle was lost and ordered an evacuation. A total of 338,000 men were shipped to safety from Dunkirk. The German army turned south again and destroyed what remained of French resistance in two weeks, using the same irresistible combination of ground mobility and air power. By 19 June, the forward units had reached the Atlantic coast. Two days earlier, the French had sued for an armistice.

It is worth reflecting that this battle was effectively won in six weeks for the loss of 29,640 German servicemen and 1,200 aircraft. Hitler was one of the many who had served for four years in the First World War, when the German army lost almost two million men and could make no progress in France for most of those four years. His air force adjutant, writing on 29 May, celebrated the ‘unheard-of pace’ of the campaign and the triumphant combination of tank and bomber; when the armistice was requested, he observed a Hitler ‘overwhelmed with emotion’ and it is not difficult to see why this common soldier turned generalissimo could scarcely believe his luck. The innovation in operational performance had been there for every power to emulate, but in 1940 only the Germans had learned the lessons of the First World War. Over the next three years, the British, Soviet and American armies and air forces each had to learn the hard way, but by 1945 they were all fighting as the Germans had done in 1940. Innovation could win a battle but it could not win the war.