The Dyle Plan

On 9 November 1939, at a conference of Allied commanders at Vincennes outside Paris, where the headquarters of the French Commander-in-Chief was housed in the medieval château, General Maurice Gamelin put forward a plan that was to decide the fate of the 1940 campaign. If the Germans attacked Belgium, the French armies and the British Expeditionary Force were not to wait for them on the Franco-Belgian border or on the nearby Scheldt, but to advance deep into Belgium, to the line of the small river Dijle (Dyle in French), from Antwerp through Louvain and Wavre to Namur, and from there along the Meuse. The British, at first reluctant to undertake so long an advance, gave way. Eight days later, on 17 November, the plan was confirmed by the Allied Supreme War Council, and Gamelin and the commander of the North-Eastern Front, General Alphonse Georges, issued the corresponding instructions.

Some accounts state that at an Anglo-French meeting at Varennes Gamelin won acceptance of the Dyle Plan, intended to keep the war away from France if Hitler invaded Belgium. The substance is correct, but the place needs correcting: the conference was held at Vincennes, the seat of French General Headquarters, not at Varennes. It should also be added that 9 November was only one stage. French documents show that the plan had been taking shape since the beginning of November and was formally adopted only on 14–17 November: after Gamelin’s meeting with Georges on 14 November, the Commander-in-Chief signed his personal and secret Instruction No. 8 on 15 November; the Supreme War Council approved the plan on 17 November; and on 25 November the commander of the 1st Army Group, General Gaston Billotte, sent his subordinates two variants of operations in Belgium: “Plan E” (for Escaut, the Scheldt) and “Plan D” (for Dyle).

The Belgian problem

For twenty years French strategy had rested on a single premise: the next war with Germany must not be fought on French soil. In 1914 Germany had occupied the industrial north of France, with its coal mines and steelworks, and held it for four years. On the border with Germany, therefore, France built the Maginot Line, which was meant to force the enemy to go round it to the north, through Belgium, as in 1914. It was there, on the plains of Flanders and Brabant, that the French army intended to stop him, by advancing to meet him on the territory of an ally. Under a secret military agreement of 1920 the French and Belgian staffs coordinated a joint defence, and in the event of danger French troops were to take their place beside the Belgians on Belgium’s eastern border.

This arrangement collapsed in 1936. After the remilitarisation of the Rhineland, to which France made no response, King Leopold III concluded that an alliance with a passive neighbour was more dangerous than helpful to Belgium, and proclaimed a “policy of independence”. Belgium renounced the military agreement, in 1937 Britain and France released it from its Locarno obligations, and Germany gave assurances that it would respect Belgian territory. In September 1939 Brussels declared strict neutrality and refused any open staff talks. The French therefore did not know exactly how the Belgians intended to defend themselves and, more importantly, could not enter Belgium until the Germans had done so or the Belgians had asked for help. Any plan to help Belgium had to assume an advance beginning at the moment when the enemy had already crossed the border.

In the autumn of 1939 it became clear that such an advance might be needed any day. After Poland’s defeat the Wehrmacht was moving division after division to the west, and on 9 October Hitler issued a directive ordering preparations for an offensive through Luxembourg, Belgium and the Netherlands. The Allies did not know its contents, but they could see troops concentrating opposite Belgium and the Netherlands. On the sector along the Belgian border Lord Gort’s British Expeditionary Force was already in position, flanked on both sides by French armies under the 1st Army Group, formed on 1 October precisely with operations in Belgium in mind.

From the Scheldt to the Dyle

The first war plans were cautious. The campaign in Poland had shown how fast German panzer divisions could advance, and Gamelin doubted whether his troops could take up positions deep in Belgium before the enemy. The instruction of 29 September gave priority to defending the fortified position along the border and envisaged intervention in Belgium only at the Belgians’ request. On 24 October Georges issued Instruction No. 7, describing the “Escaut manoeuvre”: the Allied left wing, that is the BEF and the French XVI Corps, was to wheel forward and take up position on the Scheldt as far as Ghent, while the rest of the line, from Ghent to Antwerp, was to be held by the Belgians. It was a short advance, for the British a day’s march at most, but it surrendered most of Belgium, including Brussels, to the enemy.

Over the following weeks the situation changed. The Belgian army, by now some twenty divisions strong, stopped deploying part of its forces on the French border and turned most of them east, towards Germany, to the Albert Canal and the Meuse. On the Dyle line it was building an anti-tank barrier of concrete bunkers, known as the KW Line. At the end of October Allied and Dutch intelligence reported that the Germans intended to attack the Netherlands as well, and in the first days of November that the offensive would begin on 12 November. The Belgians, alarmed, made confidential contacts with the French, although they still refused official talks. The French let them understand that they could take up position on the Antwerp–Namur line if the Belgians fortified the stretch between Wavre and Namur, where there was no water obstacle at all. The Belgian command promised to do so.

On 1 November Gamelin ordered a study of the possibility of helping the Netherlands, and on 8 November Georges signed a supplement to the plan known as the “Holland hypothesis”: the Seventh Army, the strongest of the French reserve armies, was to hurry through Belgian Flanders north of Antwerp and cover the mouth of the Scheldt. On the same day Gamelin stressed that the Germans must not be allowed to outflank Antwerp from the west. The next day, 9 November, at Vincennes, he presented to the Allied commanders a variant far bolder than the “Escaut manoeuvre”: an advance by the whole 1st Army Group to the Dyle line.

The Vincennes conference and the Supreme War Council

In Gamelin’s eyes the Dyle Plan had many advantages. The Antwerp–Louvain–Wavre–Namur–Givet line was, by various calculations, 70–80 km shorter than the Scheldt line, and so required fewer divisions. It kept most of Belgium for the Allies, including Brussels, the Belgian industrial basins and the airfields from which the Luftwaffe could attack England. It allowed more than twenty Belgian divisions, which would otherwise have to fall back on their own, to be brought into a common defence. Behind it lay the rivers Dender and Scheldt and the positions on the French border, so the defence could be organised in depth. Finally, it kept the war away from France, which for the French, who remembered the occupation of the northern departments, was the overriding aim.

The drawbacks were just as plain. For the British it meant an advance of about a hundred kilometres along unreconnoitred roads crowded with fleeing civilians, which according to the British official history was to take seven days. Success depended on the Belgians holding the enemy on the Albert Canal and the Meuse for that long, and the Allies knew little of their plans. General Georges, who was to command the manoeuvre, doubted whether the troops could reach the Dyle ahead of the Germans and dig in there before an encounter battle in the open field, which French doctrine sought to avoid at all costs. The British, including Lord Gort, his chief of staff General Henry Pownall and the Chief of the Imperial General Staff, General Edmund Ironside, viewed so long an advance with reserve. Gamelin nevertheless won them over. Gort, who commanded four divisions against dozens of French ones and was under the orders of the French command, had little room for manoeuvre in any case.

The plan was discussed for several more days, in London as well. On 14 November Gamelin went over it with Georges, and on 15 November he signed Instruction No. 8. In it he explained that the changes in the position of the Belgian army – its permanent mobilisation, its turn to the east and the fortification of the Louvain–Namur line – now gave hope that the Allied forces would be able to occupy the Antwerp–Namur position in time and establish themselves on it in strength. On 17 November the Supreme War Council met in Paris, attended by the prime ministers Neville Chamberlain and Édouard Daladier with their advisers. It resolved that, given the importance of holding the Germans as far east as possible, every effort must be made in the event of an invasion of Belgium to hold the Antwerp–Namur line. On the same day Georges issued his own Instruction No. 8, which set out the tasks of the individual armies.

Who was to stand where

Under the instruction of 17 November, at the signal of a German attack the 1st Army Group was to make a great wheel deep into Belgium, pivoting with its right wing on the Meuse near Sedan. General Henri Giraud’s Seventh Army was to stand in reserve west of Antwerp. The Belgian army, withdrawn from the Albert Canal, was to defend the sector from Antwerp to Louvain. The BEF was to occupy the Dyle line from Louvain to Wavre. The French First Army, with two light mechanised divisions and three motorised infantry divisions, was to hold the sector from Wavre to Namur, that is, the gap at Gembloux, an open plain without natural obstacles along which armies marching on Paris had passed for centuries. The mobile part of the Ninth Army was to take up position on the Meuse from Namur to the area of Givet, while the rest of it and the Second Army remained in their positions on the Meuse and on the border as far as Sedan.

The timetable was precise. On the first night the light mechanised divisions of the Cavalry Corps were to reach Gembloux, on the second the motorised divisions; on the third day the troops were to dig in, and the rest of the infantry was to arrive on the fourth day. Some divisions were left in prepared positions on the Franco-Belgian border. The Scheldt plan was not scrapped: it was to be carried out if the Germans got ahead of the Allies in Belgium. The final choice was to rest with the French command at the moment of the attack, once it became clear how long the Belgians could hold out.

The Belgians were informed of the plan only indirectly. On 19 November French General Headquarters passed them an unsigned note with “suggestions” for fortifying the Wavre–Namur position, and at the beginning of December another, asking them to coordinate their operations with the Dutch. The Belgians carried out some of the recommendations, but did not allow Allied officers to reconnoitre the ground and did not reveal their own plans. British officers inspected the Dyle line unofficially, in civilian clothes.

From the Dyle Plan to Breda

On 12 November the attack did not come. On 7 November Hitler had postponed the date of the offensive for the first time because of the weather, and he went on postponing it many more times. The Allies used the winter to build up their forces. Meanwhile Gamelin extended his plan further and further to the north. At the end of November he ordered Giraud to study an advance by the Seventh Army as far as Breda in the Netherlands to link up with the Dutch army. Georges and Billotte considered the idea very risky, because the Seventh Army was the main reserve, and if the attack came in the centre of the front, between the Meuse and the Moselle, there might be no troops left for a counter-attack. Gamelin gave way for the time being, but on 12 March 1940, after the Mechelen incident, in which German plans for an offensive through central Belgium fell into Belgian hands, he introduced the “Breda variant”. The strongest and most mobile army of the French reserve was now to race to the left wing, towards the mouth of the Scheldt and the Netherlands, instead of waiting behind the front.

The whole scheme rested on the assumption that the Germans, as in 1914, would strike with their main force across the plains of central Belgium. The British official history observes that the records of that autumn’s conferences show no sign that anyone considered what would happen if the main blow fell elsewhere. No serious offensive was expected through the Ardennes, considered difficult terrain for large armoured formations, and the sector facing them was held by the weak Second and Ninth Armies, made up largely of reserve divisions. Meanwhile, at the German Army Group A headquarters, Erich von Manstein had been arguing since the end of October that it was precisely there that a decision should be sought.

Place in the war

At dawn on 10 May 1940 the Wehrmacht attacked the Netherlands, Belgium and Luxembourg. Gamelin, woken early in the morning, gave the order to carry out the Dyle–Breda plan, and the Allied armies advanced deep into Belgium, greeted with flowers by the inhabitants. The plan was carried out largely according to the timetable, but the circumstances were different from those assumed. Fort Eben-Emael and the bridges over the Albert Canal fell on the very first day, the Belgians had to fall back much sooner than expected, and the French Cavalry Corps, which on 12–14 May fought the first great tank battle of the war at Hannut, discovered that the sector near Gembloux was far less strongly fortified than had been promised. The Seventh Army reached Breda but had to withdraw after two days, and on 14 May the Netherlands capitulated.

The outcome, however, was decided by something else. The main blow, in accordance with the German plan as revised in February, came out of the Ardennes. On 13 May the Germans forced the Meuse at Sedan and at several other points in the sector of the Second and Ninth Armies, and a few days later their panzer divisions were driving west, into the rear of the troops that had entered Belgium. The further north the Allies had advanced, the easier it was to cut them off. On 20 May German tanks reached the Channel near Abbeville, and the northern armies – the BEF, the French First Army and the Belgians – were encircled. Belgium capitulated on 28 May, and the British and some of the French were evacuated from Dunkirk.

The Dyle Plan, adopted in the autumn of 1939 to keep the war away from France, became in May 1940 one of the causes of France’s swiftest defeat. In itself it was not absurd: had the Germans attacked as they intended in November 1939, the Allies would have met them on a shorter and stronger line than the Scheldt. But it was exactly what the new German plan needed: the certainty that the best Allied armies would move north as soon as the first shot was fired. Historians today judge it above all as a misreading of the enemy’s intentions and as an example of a plan which, especially once the Breda variant was added, left no reserve for the unexpected. Gamelin, who was dismissed on 19 May 1940, defended its premises for the rest of his life.