Marine Corps University Press
Marine Corps University Press logo
Marine Corps University
Quantico, Virginia

JAMS, vol. 14, no. 1

"Trying Not to Lose It"

The Allied Disaster in France and the Low Countries, 1940

Richard J. Shuster, PhD



Abstract: This article argues that the critical point of failure in the Allied catastrophe in France and the Low Countries in 1940 was a military plan that ignored key tenets of operational art and planning. In doing so, it points out that the Allies lacked a strategy oriented toward victory, failed to balance their operational factors of time, space, and force, and planned against a single potential enemy course of action. Together, these components set the conditions for a swift Allied defeat that shocked the world. 

Keywords: World War II, strategy, Allies, military planning, France, the Low Countries



Whatever form the final triumph may take, it will be many years before the stain of 1940 is effaced.

~ Marc Bloch, 19401


The Allied debacle in 1940 that resulted in a stunning German victory in the West has been a popular subject for decades. How does France, a major military power considered to have one of the greatest armies in the world, spend 20 years planning for a war and then lose it disastrously alongside British, Belgian, and Dutch forces in a mere six weeks? A number of historians have addressed this question from a variety of perspectives. Nonmilitary studies of the defeat in 1940 have examined political, social, and cultural factors that have blamed political instability and weakness, social decay, and cultural malaise. Military explanations have focused primarily on doctrine and tactics. These studies point out that once the Germans executed Case Yellow, the assault on France and the Low Countries, the Allies were crushed, with outdated doctrine and methodical tactics proving unable to combat the revolutionary use of massed armor and supporting air power. This study, however, argues that the critical point of failure in the Allied defeat in 1940 occurred prior to the German assault and must first be laid at the doorstep of planning.

Planning has two rather simple aphorisms that indicate that it is difficult to develop a plan that achieves success without the need for refinement or absolute knowledge of enemy intentions: “No plan survives first contact with the enemy” and “the enemy gets a vote.” While it is true that any military force will have to adapt to actual conditions on the ground once a campaign or operation begins, a plan has tremendous influence on one’s ability to achieve the objective. Overall, planning can be defined as “the deliberate process of determining how (the ways) to use military capabilities (the means) in time and space to achieve objectives (the ends) while considering the associated risks.”2 A sound plan, or one that will have the best chance to achieve its objective, is one that is steeped in operational art, a collection of theoretical elements that inform the commander’s vision for a campaign or operation. If, as Professor Milan Vego of the U.S. Naval War College explains, “operational planning is the synthesis of all aspects of operational art theory and practice,” then Allied planning in 1940 illustrates a clear disregard of the principles of operational warfare.3

When drafting the campaign plan to defend against a German attack, the Allies failed to develop an effective strategy to defeat Germany or to consider and implement key elements of operational art, especially in balancing a clear military objective with the operational factors of time, space, and force. In addition, their tunnel vision in planning solely against the enemy’s most likely course of action and disregarding other more dangerous contingencies had catastrophic results. Together, these three major shortcomings that existed even before the German onslaught began in May 1940—a strategy without victory, an imbalance of operational factors, and the preoccupation with a single course of action—spelled doom for the victors of 1918.

The study of the Allied defeat by Germany in 1940 has garnered considerable attention since the end of the war and has contributed much to the understanding of the dramatic event. Memoirs, books, and articles are plentiful, each with their own unique contribution to the still growing historiography. Memoirs generally have focused on military events and actions, typically either ascribing or denying fault in the process. General Maurice Gamelin, the military mind behind the failed defense of the West in 1940, generally dismissed any personal wrongdoing and placed the onus of defeat on his subordinate commanders. His three-volume collection, Servir, contains his postwar analysis of his decisions both prior to and during the fight for France and the Low Countries. It also includes a number of contemporary orders, instructions, and letters that are critical to any understanding of the events of 1940.4 Marc Bloch’s classic account, Strange Defeat, provides the author’s insights and anguish as a French staff officer during the events.5 Other Allied memoirs of the debacle, including those by both French and British senior officers involved in the planning and execution of Allied operations in 1940, add to some of the finer details of the personalities and decisions of the period.6

Military studies of 1940, of which there are many, have tended to address the strategic and tactical levels of war. Many of these are excellent and are too numerous to cover here.7 At the strategic level, the focus of many scholarly works has been on military relations between France and its allies in both Western and Eastern Europe as well as French military policies leading up to the war such as arms production and the construction of the Maginot Line. At the tactical level, they have examined the specific actions and fighting capabilities of the Allies in defending France and the Low Countries. French doctrine and the Allied use of armor have emerged as common reasons for the defeat.8 

Missing in much of the military side of the discussion is the influence of Allied planning on the outcome of events in the spring of 1940. If, as many studies point out, French doctrine hindered the actual execution of tactical actions on the battlefield, then it was essential that the French devise a watertight plan that would maximize the Allied ability to defend the West. But this was not the case. General Gamelin and his staff, with British acquiescence, set up their forces to fail before the German offensive even began. Inadequate doctrine and faulty tactics merely exacerbated an already hopeless situation. 


Strategy without Victory 

There can be no doubt that our whole plan of campaign was wrong.

~ Marc Bloch9


Allied strategy at the eve of the Second World War was predicated upon a long war. Whereas the French and British at the start of the First World War had stated confidently that their troops would be “home by Christmas,” there was no such illusion in 1939. On the contrary, the Allies expected a war that would last years. Instead of projecting a sense of victory, Allied strategy was built around the idea of avoiding defeat. The French and British estimated that they could only muster enough military strength to be able to conduct offensive operations, let alone defeat Germany, after two years. And that was contingent on whether the Allies could defend against a German assault for that long. As it turned out, they could not, at least in regard to the continent of Europe. Instead, the war for France and the Low Countries in 1940 was over quickly, a mere six weeks, a duration that mocked Allied strategy, planning, and operations. 

From the signing of the Treaty of Versailles in June 1919 to the declaration of war with Germany in September 1939, France had focused on Germany as the primary threat to its national security. Throughout the 1920s, French diplomats established alliances and relations throughout Europe to thwart any potential German aggression, while French military leadership insisted on physical guarantees of security by stationing troops in strategic locations in the demilitarized Rhineland. Allied weapons inspectors roamed the countryside searching for illegal armaments, fortifications, and military personnel.10 Military planners focused on how to defeat Germany, revising their plans regularly throughout the interwar period. When Adolf Hitler finally unleashed his forces on the West in May 1940, the French High Command had been preparing for the war for 20 years and was only surprised that it had taken so long. 

French military strategy advocated two major phases of a war with Germany. France would first remain on the strategic defensive for upwards of two years and then transition to the strategic offensive once it, and its allied partners, had increased their military power in personnel and equipment.11 Doctrinal concepts within this strategy included the continuous front and an emphasis on firepower (particularly artillery). The strategy of a long, two-phase war was developed and endorsed by both civilian and military leadership. Although the French general staff produced a campaign plan in support of the defensive half of the strategy, it gave little thought to how to operationalize the offensive phase necessary to defeat Germany. Victory remained something to think about in the future.

Similar to the French, the British national security strategy anticipated a long war that involved a strategic defensive to offensive transition. The British planning staff developed a three-phase military strategy in the spring of 1939: defensive military operations to buy time to increase combat power, strategic bombing of Germany (while defeating Italy in North Africa), and a transition to offensive operations with an alliance with the United States in order to defeat Germany.12 They anticipated a war that would last three years.13 Similar to the French, the British conception of future offensive operations to defeat Germany remained vague. 

After an interwar period punctuated with differences in how to deal with Germany, the two former alliance partners were drawn together in the face of Hitler’s aggression. Always fearful of having to fight Germany alone, the French would not risk war without British support.14 Gamelin considered a French agreement with the British as most urgent and argued that the French could not defend their borders successfully without British military forces.15 Intelligence sharing increased and staff talks began in March 1939.16 Prior to the spring, with each side wishing to avoid war at all costs, no combined planning had been conducted. That all changed once Hitler occupied Czechoslovakia in violation of the Munich Agreement. With war on the horizon, the French and British staffs began formal discussions on a basic Allied military strategy.17 

When developing their long war strategy in 1939, the Allies had differences about potential operations in Scandinavia and the Balkans but were unanimous in their support of preventing the German occupation of Belgium and the Netherlands. Despite having no formal alliance with Belgium, French prime minister Edouard Daladier and British prime minister Neville Chamberlain wanted to provide the smaller nation with “maximum help” in the event of a German invasion. Daladier feared that German occupation of the Low Countries would threaten France’s main industrial region in the north while Chamberlain stressed that it would threaten London, southern England, and the maritime approaches with air attacks.18 They both saw benefits in keeping German forces farther to the east and advocated for the defense of as much Belgian territory as possible.19 Most importantly, the idea that Germany would focus an attack on the west in central Belgium emerged as a strategic assumption that influenced all subsequent planning.

Ironically, the Allies had planned for years to avoid the bloodletting of the First World War, and now they devised a military strategy aimed at repeating a long war of attrition followed by an ultimate offensive. The initial campaign objective was somewhat amorphous: not the defeat of Germany but the defense of a line that would be defined by the military leadership of France. What or where to defend now lay in the hands of General Maurice Gamelin, the French and Supreme Allied commander, who had been given complete freedom of action by Daladier to draft the plan to defend the West.20 Although Gamelin developed a French plan, work still needed to be done on an Allied plan. None existed when the war erupted in September 1939.21

The philosophy of planning not to lose permeated Allied thinking in 1939/40 and is evident in all of Gamelin’s plans in this period. Gamelin developed the Allied campaign plan with a laser-like focus on Belgium, and to a lesser degree the Netherlands. For years, the French High Command had been focused on a German advance through Belgium.22 Only here, Gamelin thought, could the Germans achieve decisive results.23 His operational vision, however, suffered from severe myopia. He developed three variations of a campaign plan for the defense of the West, and all three—Escaut (Plan E), Dyle (Plan D), and the Breda variant—had only slight variations of the same concept that required French and British forces to move as rapidly as possible into Belgium to check the expected German advance. 

The Allies had complete confidence in the outcome of the upcoming defensive fight, particularly in the French Army’s capabilities. Although they would later complain of a clear superiority in German capabilities, in reality the relative combat power was roughly equal, with the exception of a superiority in the size of German air forces. Chamberlain claimed that the Germans had “missed the bus” when they did not begin their offensive in 1939. When the Germans finally attacked the Low Countries on 10 May 1940, Gamelin responded with almost a smug confidence that the Allies would repel the hated enemy. His counterpart in Britain, General William Edmund Ironside, chief of the Imperial General Staff, had no doubt of Allied success.24 

Allied confidence was misplaced, to say the least. Gamelin’s plan to defend the West pleased Allied civilian leadership but his solution to avoid defeat by focusing his efforts on a defense of central Belgium would create a cascading series of disasters that Allied tactics and doctrine could not overcome. Daladier, like Gamelin, believed that the primary mission of the French Army was to prevent defeat.25 General Ironside admitted that the Allied outlook was hardly inspirational with the comment that “a war cannot, however, be won merely by trying not to lose it.”26 Yet, he threw his wholehearted support behind the plan. The commander of the British Field Force, General John Vereker Gort, stated at an Allied meeting in September 1939 that “the war can be lost in France or Belgium, even though it perhaps cannot be won there.”27 Arguing that their national interests were at stake, the British Chiefs of Staff Committee went so far as to advocate an Allied advance into Belgium if the Germans invaded the Netherlands, even if the Allies encountered Belgian resistance to their movement.28 

By the time the Germans launched their assault on the West, French and British national and military leadership were in full agreement that they would advance their forces into Belgium to defend a line that was kilometers from the French border. The French would keep the fight away from their northern industrial region and add British, Belgian, and Dutch forces in doing so. The British would protect the coastal areas that could be used to threaten Britain with air and submarine attacks. Any ideas of defeating Germany were put on hold. For now, all they had to do was to fight the Germans to a standstill, and all would not be lost. When the Germans attacked the Low Countries on 10 May, the Allies reacted methodically with their advance and confidently in their expectations to prevent the German occupation of an area that both considered critical to their national interests. When the German main effort, however, appeared in the vicinity of Sedan, far to the south of the expected enemy line of operation, the Allied strategy of a long war and its supporting defensive campaign plan were laid to waste. 


Imbalance of Operational Factors

Not only did we meet the enemy too often in unexpected places, but for the most part, especially, and with increasing frequency, in a way which neither the High Command nor, as a result, the rank and file had anticipated.

~ Marc Bloch29


Years after the end of the war, the mastermind behind the German plan to defeat France and the Low Countries, General Erich von Manstein, summarized the intent of Case Yellow simply by explaining that the Germans “just did the obvious thing; we attacked the enemy’s weakest point.”30 Those simple words illustrate the essence of operational art, more specifically the balance of operational factors of time, space, and force in order to achieve the objective. Initial German plans in 1940 placed the main effort in the north to swing through Belgium and the Netherlands, but Hitler rejected the idea as too predictable and became enamored with Manstein’s idea.31 Although the German Chief of Staff, General Franz Halder, modified Manstein’s plan, he remained true to the critical importance of placing the German main effort against the weak French center, between the onrushing Allied forces in the north and the formidable defenses of the Maginot Line to the south. For the Germans, it was the perfect setup of forces in time and space to defeat the Belgian, Dutch, and the best French and British forces in the north before executing the follow-up operation (Case Red) that would knock France out of the war. A concentration of German armor in highly mobile panzer divisions under the bold leadership of General Heinz Guderian would lead the main assault through the Ardennes to the Channel coast. For the French and British, who would send the bulk of their mobile forces racing into the Low Countries while failing to understand the importance of concentrated armor, it was a recipe for disaster (map 1).


Map 1. Plan Yellow vs. Plan D (Breda variant)

Source: Department of History, United States Military Academy, adapted by MCUP.


French plans regarding war with Germany had long focused on the need to avoid fighting on the French frontier, choosing instead to base their operational idea on an advance into Belgium. Gamelin put all of his energy into this concept, developing three variations of a campaign plan distinguishable only at the point in which Allied forces would meet their German counterparts on the field of battle in Belgium. In the fall of 1939, Gamelin had drawn up two versions of his plan—Plan E and Plan D—and in the spring of 1940, he added his third version—the Breda variant—that became the plan that the Allies executed in May. All three versions, but particularly the Breda variant, were conceptually flawed. In essence, the plans were not much more than deployment orders, with Gamelin concerned most about the need to “complete his deployment” before contact was made with German forces.32

The differences between the three versions of the plan were mainly in the locations of the Allied defensive line. Force dispositions in each plan were similar: the French 16th Corps (and then all of Seventh Army), the British Expeditionary Force (BEF), and the French First Army would move into Belgium and incorporate the Belgians into their defensive line while the French Ninth and Second Armies remained essentially static along the French frontier up until the Maginot Line. Plan E, developed by Gamelin in September, required the Allies to secure and hold the line of the Escaut River, forming a junction with Belgian forces at Ghent, as well as holding the French frontier. Forward elements would push east of the Escaut and fight a delaying action along the Dendre River while much of the Seventh Army was held in reserve near Reims. In November, Gamelin drafted Plan D, which pushed Allied forces roughly another 65–95 kilometers east to the Dyle River, along the Namur-Wavre-Louvain-Antwerp line, and incorporated the entire Seventh Army into the northern part of the line.33 Allied forces would link up with Belgian forces in the vicinity of Antwerp and attempt to occupy the Dutch islands of Walcheren and Beveland. Cavalry would advance forward to act as a screen to delay any potential German forces.34 Gamelin then added the Breda Variant in March 1940, which pushed Allied forces, specifically the French Seventh Army that had once been held in reserve, even farther to the east to Breda/Turnhout in the Netherlands. The farther east the Allies moved, however, the higher risk they incurred as they fell into the German trap.

Gamelin’s plans lacked the key ingredient for success, or in this case, the ability to employ superior (or even sufficient) force at the right time and place in order to achieve the objective. Instead, they created conditions that ceded any potential advantage to the enemy. When assuming that the Germans would concentrate on central Belgium, he employed his best equipped and most mobile forces in Belgium in the north, relied on the static Maginot Line in the south, and considered the center of his defensive lines in the rugged Ardennes area an economy of effort. The Germans, of course, attacked the weakest part of the line with overwhelming force and maneuvered with alacrity to the English Channel, cutting off Gamelin’s most precious forces in the north and then crushing the entrapped Allied forces in a classic hammer and anvil approach. 

When developing his plan to defend against a German attack, Gamelin’s fatal flaw was to focus on force in his desire to achieve parity regarding overall numbers of divisions vis-à-vis Germany. He expected his forces to defend Belgian and even Dutch territory until sufficient Allied offensive forces could be built up, forcing the Germans into a long war of attrition to offset their advantages in manpower and mobile warfare. Gamelin believed that the Allies would not have a superiority in force at any time before 1941 and would take no decisive action without it.35 With a long war strategy in mind, Gamelin envisioned a grueling repetition of the fighting in the First Word War, with Allied numbers once again eventually turning the tide in their favor. 

Gamelin’s focus on the importance of force, particularly regarding numbers of divisions, was a major factor in how and why he devised his campaign plan to move into Belgium to counter a German assault. The preoccupation with numerical equality, designing a campaign that would tally up Allied divisions and ensure continued manpower over time, was his answer to “trying not to lose it.” French preoccupation with Germany’s superior combat potential in terms of numbers of personnel can first be seen in the interwar years, when the French worked tirelessly to prevent the militarization of all sources of manpower such as the regular army, police, and paramilitary organizations.36 As the chances for war increased in the late 1930s, Gamelin had concluded that France did not have enough manpower to defend against a German assault.37 Throughout the period of the “Phony War,” Gamelin reiterated that France had a clear disadvantage in the numbers of divisions vis-à-vis Germany.38 His answer to this age old problem was to devise a campaign that would have the best chance of adding precious British, Belgian, and eventually Dutch divisions to the Allied cause. In this manner, he could create numerical equality with the Germans and then fight a largely static form of warfare until he was able to build up a numerical superiority to shift to the offensive. When Germany attacked in May, Gamelin had successfully evened the score as far as force. In fact, 135 German divisions faced 151 Allied divisions.39 In reaching parity, however, Gamelin had actually sacrificed advantages in space and time and increased risk to the mission and to his forces. 

Gamelin’s intent to increase Allied forces was centered first and foremost on the need to keep Britain in the fight. Although the size of the BEF was small in this period, a mere 10 divisions by May 1940, Gamelin envisaged a long war, and over time Britain would be able to produce a large number of quality divisions to help tip the scales against any German force advantage. According to Colonel Jacques Minart, who served on Gamelin’s staff in 1939–40, Gamelin’s impetus to move his forces into Belgium was his fear that the German occupation of Belgium and the Netherlands would knock the British out of the war or at least force them to withdraw from the continent.40 Ironically, of course, this decision helped lead to France’s defeat while Britain was able to survive the German capture of the Low Countries and the subsequent air attack on Britain. 

Fear of losing British support weighed on Gamelin at the start of the war. In one of his first meetings with the British in September, Gamelin claimed that he needed as much British help as possible to defend against the expected German attack in the Low Countries.41 French intelligence produced reports that influenced Gamelin in the fall, warning that Germany had the potential to double its current military strength with the reconstitution and training of military age personnel.42 The French military representatives who had been having staff conversations with the British warned in September that German occupation of the Flemish coast would create serious danger for Britain.43 In October, Gamelin urged General Ironside to increase the number of British divisions to the continent, emphasizing the “necessity of the common effort which we must undertake in regard to effective strengths so that we may not find ourselves this coming Spring in a dangerous state of inferiority in face of the German forces.”44 Ironside was well aware of Gamelin’s force sensitivity and understood that the French would “continue to pressure us to send the maximum number of divisions to France.”45 The British questioned Gamelin’s plans at times, particularly force dispositions and defensive preparations, but never the idea to move into Belgium.46 

When focusing on force, Gamelin also planned to add Belgium’s 22 divisions to the Allied defense against Germany. His desire to incorporate Belgian divisions into the Allied defense was a consistent theme in his planning, another number that he could add to the force balance sheet to offset German force advantages. In drafting Plan E in September, Gamelin argued that his force dispositions in Belgium along the Escaut would allow the Belgian Army to reconstitute its forces (expected to be in combat with the Germans) and “to take its place on the Allied front.”47 He believed that employing his forces along the south bank of the Escaut River had defensive advantages, but more importantly would rally the Belgians, adding their divisions to the Allied defense against the German attack.48 He repeated his desire to rally the Belgians and incorporate their forces into the Allied defensive line in another meeting with the British on 19 November.49 

Finally, Gamelin envisioned the Allied move into Belgium could be a way of adding Dutch forces to his overall plan. First considered in a September instruction to Georges, he pointed out that his Plan E to move into Belgium would be a prelude to any land support given to the Netherlands.50 During Allied meetings in November 1939, when Gamelin presented his Dyle version of his campaign plan to the British, he also began to examine the question of how to add the Dutch to the Allied force mix. At this point Gamelin had long since settled on a plan based on Allied movement into Belgium but now laid out his plan for an Allied move to the Dyle that included sending forces into Dutch territory as well. Elements of the French Seventh Division on the far left of the Allied line would occupy the mouth of the Escaut and the two Dutch islands of Walcheren and Beveland to link up with Dutch forces. More importantly, he emphasized the disadvantage in French force numbers and that the additional 22 Belgian and 10 Dutch divisions were necessary to even out the numbers against Germany.51

Gamelin eventually relented completely to his force preoccupation in his Breda variant of the Dyle Plan. After warning Daladier in January 1940 that he needed to address the lack of Allied “numerical equality” with the Germans, he modified his plan further to ensure the addition of Dutch divisions and to help protect Belgian forces.52 In an instruction to George on 12 March 1940, Gamelin first pointed out that the Dyle Plan placed the Seventh Army north of Antwerp in order to ensure the security of the lower Escaut and to forge a connection with the Belgians and Dutch. To maintain communication with the Dutch and add their forces to the Allied defensive line, Gamelin now pushed the Seventh Army even farther to the east, toward the Breda-Saint-Leonard or even the Tilburg-Turnhout line. He argued that this extension of the Allied front to the east would actually reduce risk to his forces in helping to reinforce the Belgian forces against the German assault.53 Now, elements of the Seventh Army would extend another 48 kilometers to the east, farther away from the French frontier, and to the extreme north of the Allied line, isolated from the main fighting that would soon take place 240 kilometers to the south.

Gamelin’s subordinate commanders’ concerns with the Breda variant fell on deaf ears. Georges was one of the only voices though that brought up the uncomfortable notion that the Germans may not attack in strength in Belgium but rather make their main effort possibly in the center of the French defensive line. He complained that the new modifications to the Dyle Plan stripped away his reserve forces and placed them far to the north. Gamelin, however, rebuffed Georges’s critique, arguing that it was out of the question to abandon the Netherlands and that it was necessary “to make an effort to at least give a hand to the Dutch and try to have a land communication with them.”54 In exchange for 10 Dutch divisions that were overwhelmed quickly by the Germans in May, Gamelin had further entrapped some of his best forces far to the north, with little hope of either holding the secondary German effort in the north or supporting the Allied defense against the German primary effort to the south.

The focus on increasing force by advancing into Belgium led to an imbalance with time and space that the Allies could simply not overcome once the fighting erupted. When Allied intelligence reported that the long anticipated German attack had begun, French and British forces followed Gamelin’s tragic script. They reached the Dyle line with little resistance, as the Seventh Army moved steadily toward Breda, and along with the BEF, engaged what they thought was the German main effort in central Belgium. Large engagements with German Army Group B occurred in Hannut and Gembloux to prevent the Germans from crossing Gamelin’s “open plains” of Belgium, while the bulk of German armored divisions in Army Group A overran the much smaller Belgian forces in the Ardennes and the French forces in Sedan. The Allied line crumbled. 

With all their planning focused on moving into Belgium, neither France nor Britain gave much, if any, thought to the time it may take to employ their forces anywhere else. Once locked into combat with German forces, the Allies faced a difficult fighting withdrawal, and any notion of repositioning their best forces to meet the German main effort along the Meuse in the Sedan area was overcome by the tyranny of distance and time. The French had also failed to assess with any accuracy the area facing the center of their defensive line. Overestimating the defensive value of both the Ardennes and the Meuse, these natural defenses were rendered impotent when faced with overwhelming local superiority of force. Most importantly, the Germans had a far superior force-to-space ratio in the sector of main effort and the point of main attack—the area between Sedan and Dinant.55 With the Allies locked in a ferocious battle with German armored and infantry forces in Belgium, they were unable to disengage their best forces to meet the concentrated German armored forces 240 kilometers to the south that were breaching the Meuse River in the Sedan area and would soon reach the English Channel coast. 


Scripting Disaster: Tunnel Vision and Mirror Imaging

Only the most elastic of minds can make sufficient allowance for the unexpected—which means, in most cases, what the enemy will do

~ Marc Bloch56


When the Germans attacked on the morning of 10 May 1940, Gamelin, in reference to his Dyle/Breda Plan, asked his subordinate commander: “Since the Belgians have appealed to us, can you see how we can do anything else?”57 Georges affirmed the expected response; there simply was no other plan.58 The rigid adherence to what amounted to a single course of action reveals a stunning lack of creativity and sound operational thinking. The Allies had written a script on how to fight Germany with a singular focus on moving into Belgium as quickly as possible, memorized it in full, and then performed it with aplomb. The French Seventh Army arrived in the vicinity of Breda, British forces reached the Dyle, and the French First Army arrived on the Wavre-Namur line, all with no significant issues. Now the Germans just had to follow the same script and the Allies would be the saviors of Europe once again. The Germans, however, had other ideas. Manstein’s belief that the best solution was not necessarily the most logical solution—because the enemy could be planning along identical lines—is both simple and instructive.59

Campaign and operational planning are most effective when multiple courses of action are generated to achieve an objective, and then each course of action is evaluated against potential enemy courses of action. This is an art, not a science, and therefore relies on the application of sound military theory, with a dose of creativity. Yet, the Allies had developed only slight variations of one course of action that matched up perfectly with a single, most likely German course of action. In most cases a commander does not have a perfect awareness of enemy intentions so it is imperative to consider the impact that various potential enemy actions could have upon one’s forces in order to improve the effectiveness of the plan. In theory and practice, the Germans understood that it was wise to adopt the enemy’s most dangerous enemy course of action as a basis for one’s planning in order to reduce risk.60 Current U.S. joint doctrine, for instance, stipulates that each friendly course of action should be analyzed (or wargamed) against the enemy’s most likely and most dangerous courses of action. In his postwar memoirs, Gamelin even admits that “one must always plan for the worst”61 In 1939–40, however, the French and British ignored theory and logic and instead based their plan on wishful thinking.

Gamelin personally devised the Dyle/Breda Plan based on an enemy response that illustrated what he would have done—classic mirror imaging. In this case, his lack of creativity and application of sound theory led him to believe that the main German effort would be on the “open plains” of Belgium.62 This mirror imaging satiated his desire to secure British support and add Belgian and Dutch divisions to the Allied defense but left his forces unprepared to deal with any contingencies. Ironically, the original German plan was to advance exactly as Gamelin had anticipated, but Adolf Hitler dismissed it as another Schlieffen Plan that lacked any original thinking. In the Allied case, however, strategic leadership never questioned its creativity or potential to deceive the enemy. They all assumed, like Gamelin, that the Germans would focus their main effort in that area.

Allied tunnel vision on a single course of action planned against a single German course of action was apparent early in the planning process. In September 1939, as Gamelin pondered his Escaut Plan, he had already assumed the German weight of main effort would be across the Belgian plains. In an instruction to Georges, Gamelin was only concerned with the amount of time it would take Allied forces to reach the proper defensive line in Belgium before meeting the German main effort (gros de l’effort).63 General Howard Vyse, the British director of military operations, reported that Gamelin was preoccupied with a German attack on the Low Countries, thinking that it represented an “audacious” move.64 Ironically, Gamelin referred to a German move into Belgium as “the most dangerous” because it could have the fastest results.65 He told Ironside in mid-September that the Germans would attack through the neutral countries, and he never wavered from this belief.66 Preoccupation turned to negligence, as the Allies were completely unprepared to deal with the ultimate German plan to breach the Meuse in the center of the Allied line and race to the English Channel.

The only exceptions to the Allied exclusive focus on Belgium were some fleeting thoughts that the Germans could attempt to attack through Switzerland or to outflank the Maginot Line. During a meeting with his Allied counterparts on 6 October 1939, Gamelin raised the idea of a German attack through Switzerland but quickly dismissed it as unlikely.67 Gamelin also revealed that he had considered the possibility of a German attack through Luxembourg and the Ardennes, moving southward behind the Maginot Line.68 This potential German course of action, however, never emerged in the critical Allied discussions in November, or frankly at all. If such a contingency had been planned, and then executed as a branch plan in May 1940 once the Germans revealed their true intentions, the outcome of 1940 could have been a far cry from what occurred. At the start of the war, Gamelin had pointed out to Georges the need to maintain large strategic and tactical level reserves behind the lines.69 In the end, it is curious that Gamelin designed his campaign plan to meet the defensive Allied strategy of a long war by stripping his reserves away from the center, where they could most easily reach any part of the defensive line and employing them in the far reaches of his left wing. 

Historians have examined the role of intelligence in how it supported the Allied response to the German assault, but a study on the link between operational intelligence and Allied planning in 1940 has yet to be written. Was Gamelin’s fixation on a German attack in Belgium supported by intelligence? It is difficult to say. Gamelin later claimed to be ill-informed of the direction of the main German attack through the Ardennes.70 Allied intelligence, at least at the tactical level, did report German armored columns snaking through the Ardennes in the early hours of the German assault. At the operational level of war, however, Allied intelligence focused on German capabilities, particularly the number of divisions available for combat in the West but ignored potential German intentions that could have influenced Allied planning. Ernest May, in Strange Victory, argues that French intelligence had uncovered many clues that pointed to an attack through the Ardennes but that nobody was able to synthesize these snippets of information in an accurate estimate of German intentions.71 

It is also difficult to ascertain whether Gamelin would have listened to such heresy and changed his plan accordingly. Making significant modifications to all the detailed planning of meticulous timetables that focused on getting Allied forces to the proper defensive line in Belgium would have been quite challenging after months of beating the same drum over and over. The British were also in complete agreement concerning what they considered to be the German intent.72 A sound plan, however, should always reflect any changes in the situation. As it turned out, when the situation did reveal that the Allies had erred in their assumption of the German main effort in Belgium, it was left to subordinate commanders to conduct ad hoc/crisis action planning. The German tempo, however, disrupted any potential Allied decision-making cycle to produce a coordinated response. 

Stealing a phrase from Neville Chamberlain in reference to Hitler not launching an assault on the West in 1939, the Allies “missed the bus” on German intentions. In planning, an assumption is made to continue planning when something is unknown. In other words, a likely conclusion or judgment is made in the absence of facts. Much like Allied leaders assumed that the Germans would turn west after the completion of their campaign in Poland, they assumed that Germany would concentrate their forces in Belgium because the terrain was suited for the offense and that was where the Germans had been successful in the previous war. Of course, going back to the war prior to that one could have shed some light on a more dangerous possibility—that the Germans would employ superior force in the area of Sedan. Instead, Allied plans began to treat their assumption of the main German assault in Belgium as a fact instead of the grave risk that such an assumption represented.

In his postwar memoirs, Gamelin incredulously defended his plan to advance into Belgium by claiming that “staying on our border was the easy way out . . . it was, indeed, tempting.”73 In his mind, a German takeover of Belgium would physically and diplomatically sever France and Britain and put an end to a united front against the common enemy.74 He only had to keep the Germans locked in a stalemate and eventually the British would send enough troops to give him the force superiority that he believed was a prerequisite of success. This stubborn adherence to a preconceived idea, with little attention paid to any other contingency, played right into German hands. Avoiding defeat instead became a self-fulfilling prophecy.



In other words, the German triumph was, essentially, a triumph of intellect.

~ Marc Bloch75


During the six weeks of the campaign in the west in 1940, the Allies suffered approximately 100,000 killed in action, roughly equal to the amount the United States lost in all four years of bitter fighting in the Pacific. This staggering number of dead in a relatively brief period underscores the point that Allied soldiers paid a steep price for the mistakes of their strategic civilian and military leadership. Armed with a strategy that had no clear vision of victory, Gamelin had devised a campaign plan that ignored key facets of operational art and sound planning. Many more soldiers and civilians would soon pay the price for that failure. 

Lessons learned from the Allied debacle in 1940 are numerous. As far as the execution of the Allied plan, previous studies have drawn conclusions on the faulty employment of Allied armor, the exposure of the linear front concept to maneuver warfare, the methodical nature of the French employment of forces, and antiquated command and control. This study has examined the topic from a strategic and operational viewpoint prior to the actual campaign, examining the rationale and implications of a strategy that lacked a clear vision of victory, a campaign plan that did not balance operational factors, and planning that never accounted for a potential most dangerous enemy course of action. These were the critical ingredients that set up the French and British forces to fail. 

The Allied long war strategy, developed at the start of the war, had no clear vision of victory. Instead, the French and British planned to defend their national interests with a war of attrition in Belgium for at least two years to build up superior combat power for offensive operations in the future. The War to End All Wars was now a blueprint for success. The Allied focus on defending Belgium operationalized the long war strategy, as it appealed to both nations’ strategic concerns and addressed Gamelin’s quest to even the force score with Germany. It was the only contingency, and with few exceptions everyone accepted it without question. More than just an example of group think, it was a plan that appeased each Allied nation’s fears. The French could move the dreaded front away from French territory with the added prestige of protecting their neighbors. For the British, it meant that they could concentrate their land forces on the continent as close to Britain as possible and use their naval and air assets in support without compromising national security. But a second phase of the Allied campaign to conduct offensive operations to defeat Germany never even reached the planning stages. Gamelin had planned a half measure; it was a defensive campaign with no concept to link it to subsequent operations.

Gamelin’s fixation on force, illustrated by his campaign plan to ensure the addition of British, Belgian, and Dutch forces through a concentrated move into Belgium, tipped the balance of time, space, and force and prevented the Allies from achieving their objective of defending France and the Low Countries. In support of the Allied long war strategy, Gamelin had ensured the continued support of British forces and anticipated adding Belgian and Dutch divisions to his force ledger. In doing so, he satiated his own preoccupation with force that he believed was instrumental in preventing defeat. Gamelin had concluded that this could only be done by defending Belgium and Dutch territory. He therefore positioned his best forces at the northernmost point in the defensive line, ready to prevent the Germans from exploiting the flat terrain in Belgium and outflanking them at the coast. As a result, he was unable to meet the actual German main effort in the area of Sedan, as the superior enemy concentration of force at the right time and place, coupled with a high operational tempo, shredded the Allied long war strategy and revealed Gamelin’s campaign plan as a paper tiger.

The Allies had put all their effort into one plan against the most likely enemy course of action—a German advance across Belgium—accepting enormous risk in doing so. They ultimately fought the campaign that they had envisioned for months, not the campaign that the actual situation demanded. When the Germans simply focused on the weakest part of Gamelin’s long-planned Allied defensive line, there was no contingency plan to meet it and no chance to reposition their best forces in time. Months of planning around a single option had led to a predictable plan, and for the Allies, a predictable result. With no serious consideration of contingency plans, Gamelin had gambled everything on a German most likely course of action that pleased his political masters but proved to be nothing more than his own wishful illusion. In the end, the Allied plan did not survive first contact with the enemy. The enemy had gotten a vote too.


  1. Marc Bloch, Strange Defeat: A Statement of Evidence Written in 1940 (New York: Octagon Books, 1968), 175.
  2. Joint Planning, Joint Publication 5-0 (Washington DC: Office of the Chairman of the Joint Chiefs of Staff, 2017).
  3. Milan Vego, Joint Operational Warfare: Theory and Practice (Newport, RI: U.S. Naval War College, 2007), ix–63.
  4. Maurice Gustave Gamelin, Servir, 3 vols. (Paris: Plon, 1946).
  5. Bloch, Strange Defeat.
  6. See, for instance, Jacques Minart, P.C. Vincennes, Secteur 4 (Paris: Editions Berger-Levrault, 1945); Adolphe Goutard, The Battle of France, 1940 (New York: Ives Washburn, 1959); and Roderick Macleod and Denis Kelly, Time Unguarded: The Ironside Diaries, 1937–1940 (New York: David McKay, 1962).
  7. Classic studies of the events include Alistair Horne, To Lose a Battle: France 1940, rev. ed. (London: Penguin Books, 1990); and William L. Shirer, The Collapse of the Third Republic: An Inquiry into the Fall of France in 1940 (New York: Simon and Schuster, 1969); and Martin S. Alexander, The Republic in Danger: General Maurice Gamelin and the Politics of French Defence, 1933–1940 (Cambridge, UK: Cambridge University Press, 1992). More recent studies include Ernest R. May, Strange Victory: Hitler’s Conquest of France (New York: Hill and Wang, 2000); Julian Jackson, The Fall of France: The Nazi Invasion of 1940 (Oxford, UK: Oxford University Press, 2003); Joel Blatt, ed., The French Defeat of 1940: Reassessments (New York: Beghahn Books, 1998); Lloyd Clark, Blitzkrieg: Myth, Reality, and Hitler’s Lightning War, France 1940 (New York: Atlantic Monthly Press, 2016); and Philip Nord, France 1940: Defending the Republic 1940 (New Haven, CT: Yale University Press, 2015).
  8. Robert A. Doughty, The Seeds of Disaster: The Development of French Army Doctrine, 1919–1939 (Hamden, CT: Archon Books, 1985); and Robert A. Doughty, The Breaking Point: Sedan and the Fall of France, 1940 (Hamden, CT: Archon Books, 1990). The author argues that French emphasis on the methodical battle and centralized decision making were critical to the overall French failure in 1940.
  9. Bloch, Strange Defeat, 39.
  10. French and British enforcement of the military clauses of the Treaty of Versailles, despite German obstruction efforts, were largely successful in diminishing German military strength from 1920–31. See Richard J. Shuster, German Disarmament of Germany after World War I: The Diplomacy of International Arms Inspection, 1920–31 (London: Routledge, 2006). 
  11. Alistair Horne, To Lose a Battle: France 1940, rev. ed. (London: Penguin Books, 1990), 169; and Robert Young, “La Guerre de Longue Dureé: Some Reflections of French Strategy and Diplomacy in the 1930s,” in General Staffs and Diplomacy Before the Second World War, ed. Adrian Preston (London: Croom Helm, 1978), 46–49.
  12. David Dilks, “The Unnecessary War?: Military Advice and Foreign Policy in Great Britain, 1931–1939,” in General Staffs and Diplomacy Before the Second World War, 129.
  13. CAB[inet papers] 80/9, “Certain Aspects of the Present Situation,” 26 March 1940, Kew, United Kingdom, National Archives; and Nick Smart, British Strategy and Politics During the Phony War: Before the Balloon Went Up (Westport, CT: Praeger, 2003), 73.
  14. Young, “La Guerre de Longue Dureé,” 58.
  15. [Vincennes, France, Service historique de la Défense, Centre historique des archives], GR 5N 579, Gamelin to Minister of National Defense, 4 April 1938; and GR 5N 579, Gamelin, “Note sur la Collaboration Militaire Franco-Britannique,” 24 April 1938. 
  16. Peter Jackson and Joseph Maiolo, “Strategic Intelligence, Counter-Intelligence and Alliance Diplomacy in Anglo-French Relations Before the Second World War,” Militärgeschichtliche Zeitschrift 65, no. 2 (2006): 453–54.
  17. Up to this point, there had been only low-level contacts between service attachés. See Martin S. Alexander and William J. Philpott, ed., Anglo-French Defence Relations Between the Wars (New York: Palgrave Macmillan, 2002), 106, 211; Eleanor M. Gates, The End of the Affair: The Collapse of the Anglo-French Alliance, 1939–40 (Berkeley: University of California Press, 1981), 16; L. F. Ellis, The War in France and Flanders, 1939–1940 (London: Her Majesty’s Stationary Office, 1953), 4; and Allan R. Millett and Williamson Murray, Military Effectiveness, vol. 2, The Interwar Period (Boston: Allen & Unwin, 1988), 109–10. 
  18. Gamelin, Servir, vol. 1, 145–46. His quest for military manpower played a significant role in his decision to move into Belgium and will be explored in the next section. 
  19. GR 5N 580, Decisions of the Supreme Council, 17 November 1939; Smart, British Strategy and Politics During the Phony War, 86; and Gamelin, Servir, vol. 3, 146.
  20. W[ar]O[ffice papers] 106/1684, Director of Military Operations and Plans, Notes of a Meeting Held at the Headquarters of General Gamelin, 9 November 1939, Kew, United Kingdom, National Archives.
  21. WO 106/1684, War Office to British Military Attaché, 4 September 1939. 
  22. Doughty, The Seeds of Disaster, 65–67. 
  23. Smart, British Strategy and Politics During the Phony War, 81; and Millett and Murray, Military Effectiveness, vol. 2, 46.
  24. Roderick Macleod and Denis Kelly, Time Unguarded: The Ironside Diaries, 1937–1940 (New York: D. McKay, 1962), 297.
  25. Smart, British Strategy and Politics During the Phony War, 77.
  26. CAB 80/104, Ironside Memo, 24 January 1940. 
  27. WO 106/1684, Hore-Belisha Note, 21 September 1939. 
  28. CAB 80/105, Chiefs of Staff Committee, German Invasion of Holland: Allied Policy Draft Memorandum, 5 April 1940; CAB 80/105, Chiefs of Staff Committee, German Invasion of Holland: Air Policy Report, 8 April 1940; and CAB 80/10, Chiefs of Staff Committee, Allied Action in the Event of a German Attack on the Netherland Islands, 1 May 1940. 
  29. Bloch, Strange Defeat, 48.
  30. Alistair Horne, To Lose a Battle: France 1940 (London: Penguin, 2007), 677 notes. 
  31. Karl-Heinz Frieser, The Blitzkrieg Legend: The 1940 Campaign in the West (Annapolis, MD: Naval Institute Press, 2005), 60–67. 
  32. CAB 66/1/44, Conversation with M. Daladier and General Gamelin, Note By the Secretary of State for War and Lord Hankey, 21 September 1939. 
  33. WO 106/1684, Notes of a Meeting Held at the Headquarters of General Gamelin, 9 November 1939; WO 106/1684, General Staff to C.I.G.S., 20 April 1940. 
  34. Gamelin, Note (Georges), 5 November 1939, Servir, vol. 3, 140–41. 
  35. GR 5N 580, Gamelin to Minister of National Defense, “Plan de guerre pour le printemps 1940,” 26 February 1940. 
  36. Shuster, German Disarmament of Germany After World War I, 72–73.
  37. Gamelin, Servir, vol. 1, 36.
  38. See, for instance, CAB 80/3, General Gamelin’s Observations, 27 September 1939; CAB 80/3, Chiefs of Staff Committee, Comments on General Gamelin’s Observation on our Appreciation on the Possible Course of the War, 2 October 1939; and Gamelin to Daladier, 7 January 1940, Servir, vol. 3, 153–54. 
  39. Karl-Heinz Frieser, The Blitzkrieg Legend: The 1940 Campaign in the West (Annapolis, MD: Naval Institute Press, 2005), 36; and Clark, Blitzkrieg, 94. There is some variation among sources in the overall and individual nation numbers but there certainly was not a German force advantage in terms of number of divisions. 
  40. Minart, P.C. Vincennes, Secteur 4, Tome I, Titre II, 151–52. 
  41. CAB 80/104, Notes of a Meeting at the Headquarters of Gamelin, 21 September 1939. 
  42. CAB 66/2/50, Gamelin to Secretary of State for War, 20 October 1939.
  43. CAB 80/3, French Permanent Military Representatives, Note Relative to Operations in Holland, Belgium, and Luxembourg, 24 September 1939.
  44. CAB 66/2/50, 2nd Bureau, Note on the Available Personnel of Germany, 14 October 1939.
  45. CAB 80/104, Ironside Memo, 24 January 1940.
  46. WO 106/1684, Dewing to Pownall, 23 September 1939; WO 106/1684, British Chiefs of Staff Draft Letter to Gamelin, September 1939; and WO 106/1684, General Staff Criticism of General Gamelin’s Plan, September 1939.
  47. WO 106/1684, Extract of a Letter from Gamelin to CIGS, 23 September 1939.
  48. Gamelin, Instruction No. 6, 29 September 1939, Servir, vol. 3, 83. 
  49. WO 106/1684, Suggestions, 19 November 1939.
  50. Gamelin, Instruction No. 7 (Georges), 30 September 1939, Servir, vol. 3, 85.
  51. Gamelin, Instruction Personnelle et Secrète No 8, 15 November 1939, Servir, vol. 1, 82–93. 
  52. Gamelin to Daladier, 7 January 1940, Servir, vol. 3, 153–54.
  53. Gamelin, Instruction Personnelle et Secrète No 11 (for Georges), 12 March 1940, Servir, vol. 3, 177.
  54. Gamelin to Georges, 15 April 1940, Servir, vol. 3, 343.
  55. Vego, Joint Operational Warfare, iii–55.
  56. Bloch, Strange Defeat, 115–16.
  57. May, Strange Victory, 385.
  58. L. F. Ellis, The War in France and Flanders, 19391940, 22.
  59. Frieser, The Blitzkrieg Legend, 69.
  60. Vego, Joint Operational Warfare, ix–45. 
  61. Gamelin, Servir, vol. 1, 346.
  62. Gamelin, Servir, vol. 1, 336.
  63. Gamelin, Servir, vol. 3, 83–84.
  64. WO 106/1684, Notes Sent by General Howard Vyse, 12 September 1939.
  65. CAB 80/104, Notes of a Meeting Between Gamelin and CIGS, 6 October 1939.
  66. WO 106/1684, Gamelin to Ironside, 18 September 1939. Gamelin dated his letter 1839.
  67. CAB 80/104, Notes of a Meeting Between Gamelin and CIGS, 6 October 1939.
  68. WO 106/1684, CIGS to Wavell, 10 October 1939.
  69. Gamelin, Note (Georges), 21 September 1939, Servir, vol. 1, 245–47.
  70. Gamelin, Servir, vol. 1, 336.
  71. May, Strange Victory, 5.
  72. CAB 80/104, Ironside Memo, 24 January 1940.
  73. Gamelin, Servir, vol. 1, 337.
  74. Gamelin, Servir, vol. 3, 135.
  75. Bloch, Strange Defeat, 36.

About the Author

Dr. Richard J. Shuster is a professor in the Joint Military Operations Department at the U.S. Naval War College. He has a PhD in history from George Washington University and is the author of German Disarmament After World War I: The Diplomacy of International Arms Inspection, 1920–1931 (2006). From 2004–12, Dr. Shuster worked for the Defense Intelligence Agency as a historian and representative to the Naval War College.

The views expressed in this article are solely those of the author. They do not necessarily reflect the opinions of Marine Corps University, the U.S. Marine Corps, the Department of the Navy, or the U.S. government.

Marine Corps University