The Schlieffen Plan

The Schlieffen Plan was a deployment plan and operational guide for a decisive initial offensive campaign in a one-front war against the French Third Republic. In 1914 it was deployed against two fronts with major changes by Commander-in-Chief Moltke the Younger, resulting in a failure to achieve the decisive victory Schlieffen had planned.

The Schlieffen Plan was the strategy for the German invasion of France and Belgium in August 1914. Field Marshal Alfred von Schlieffen was the Chief of the Imperial Army German General Staff from 1891 to 1906 and in 1905-06 devised a deployment plan for a winning offensive in a one-front war against the French Third Republic. After the war, German historians and other writers described the plan as a blueprint for victory. Some claimed the plan was ruined by Colonel-General Helmuth von Moltke the Younger, the Commander-in-Chief of the German army after Schlieffen retired in 1906 who was dismissed after the First Battle of the Marne (September 5-12, 1914).

Alfred von Schlieffen’s War Planning

The cornerstone of Schlieffen’s war planning was undoubtedly the strategic counter-offensive. Schlieffen was a great believer in the power of the attack in the context of the defensive operation. Germany’s smaller forces relative to the Franco-Russian Entente meant that an offensive posture against one or both was basically suicidal. On the other hand, Schlieffen placed great faith in Germany’s ability to use railways to launch a counter-offensive against a hypothetical French or Russian invasion force, defeat it, then quickly regroup and launch a counter-offensive.

Schlieffen also recognized the need for offensive planning, as failing to do so would limit the German Army’s capabilities. In 1897, Schlieffen developed a tactical plan that – acknowledging the German army’s limited offensive power and capacity for strategic maneuvers – basically amounted to using brute force to advance beyond the French defenses on the Franco-German border.

In 1905, Schlieffen developed what was truly his first plan for a strategic offensive operation, the Schlieffen plan Denkschrift (Schlieffen plan memorandum). This was designed for an isolated Franco-German war that would not involve Russia, calling for Germany to attack France.

However, the bulk of Schlieffen’s planning followed his personal preferences for the counter-offensive. Schlieffen’s war plans by the name of Aufmarsch II and Aufmarsch Ost continued to stress that Germany’s best hope for survival in a war with the Franco-Russian entente was a defensive strategy. This was reconciled with a very offensive tactical posture as Schlieffen held that the destruction of an attacking force required that it be surrounded and attacked from all sides until surrender, not merely repulsed as in a passive defense.

In August 1905 Schlieffen was kicked by a companion’s horse, rendering him incapable of battle at age 72. He began planning his retirement, but his successor was undetermined. A favourite of the Emperor was Helmuth von Moltke the Younger, who became Chief of Staff after Schlieffen retired.

Moltke went on to devise Aufmarsch II Ost, a variant on Schlieffen’s Aufmarsch Ost designed for an isolated Russo-German war. Schlieffen seemingly tried to impress upon Moltke that an offensive strategy against France could only work in the event of an isolated Franco-German war, as German forces would otherwise be too weak to implement it. Knowing this, Moltke still attempted to apply the offensive strategy of Aufmarsch I West to the two-front war Germany faced in 1914 and Schlieffen’s defensive plan Aufmarsch II West. With too few troops to cross west of Paris let alone attempt a crossing of the Seine, Moltke’s campaign failed to breach the French “second defensive sector” and his troops were pushed back in the Battle of the Marne.

Post-war writing by senior German officers like Hermann von Kuhl, Gerhard Tappen, Wilhelm Groener, and official historians led by the former Lieutenant-Colonel Wolfgang Förster established a commonly accepted narrative that it was Moltke the Younger’s failure to follow the blueprint rather than German strategic miscalculation that condemned the belligerents to four years of attrition warfare instead of the quick, decisive conflict it could have been.

Deployment of the Schlieffen Plan

At the outbreak of World War I, 80% of the German army was deployed as seven field armies in the west according to the plan Aufmarsch II West. However, they were then assigned to execute the retired deployment plan Aufmarsch I West, from the Schlieffen Plan. This would march German armies through northern Belgium and into France in an attempt to encircle the French army and breach the “second defensive area” of the fortresses of Verdun and Paris and the Marne river.

Aufmarsch I West was one of four deployment plans available to the German General Staff in 1914. Each favored certain operations but did not specify exactly how those operations would be carried out, leaving the commanding officers to do so at their own initiative with minimal oversight. Aufmarsch I West, designed for a one-front war with France, was retired once it became clear it was irrelevant to the wars Germany could expect to face. Both Russia and Britain were expected to help France with no possibility of assistance from Italian or Austro-Hungarian troops. But despite its unsuitability and the availability of more sensible and decisive options, it retained a certain allure due to its offensive nature and the pessimism of pre-war thinking, which expected offensive operations to be short-lived, costly in casualties, and unlikely to be decisive. Accordingly, the Aufmarsch II West deployment was changed for the offensive of 1914, despite its unrealistic goals and the insufficient forces Germany had available for decisive success. Moltke took Schlieffen’s plan and modified the deployment of forces on the western front by reducing the right wing, the one to advance through Belgium, from 85% to 70%. In the end, the Schlieffen plan was so radically modified by Moltke that it could be more properly called the Moltke Plan.

Germany attacked Luxembourg on August 2 and on August 3 declared war on France. On August 4, after Belgium refused to permit German troops to cross its borders into France, Germany declared war on Belgium as well. Britain declared war on Germany on the same day following an “unsatisfactory reply” to the British ultimatum that Belgium must be kept neutral.

In the end, Germany failed to avoid a long, two-front war, but had fought its way into a good defensive position inside France and effectively halved France’s supply of coal. It had also killed or permanently crippled 230,000 more French and British troops than it itself had lost. Despite this, communications problems and questionable command decisions cost Germany the chance of a more decisive outcome.

Schlieffen Plan: One historian’s depiction of the Schlieffen Plan in red dotted lines.

Early Battles

Following the outbreak of war in August 1914, the German Army opened the Western Front by invading Luxembourg and Belgium, but were forced back with the Battle of the Marne.

Battle of Liège

At the outbreak of the First World War, the German Army (consisting in the west of seven field armies) executed a modified version of the Schlieffen Plan, designed to quickly attack France through neutral Belgium before turning southwards to encircle the French Army on the German border. Belgium’s neutrality was guaranteed by Britain under the 1839 Treaty of London; this caused Britain to join the war at the expiration of its ultimatum at 11 p.m. GMT on August 4, 1914, when armies under German generals Alexander von Kluck and Karl von Bülow attacked Belgium. Luxembourg had been occupied without opposition on August 2. The first battle in Belgium was the Siege of Liège, which lasted from August 5-16. Liège was well-fortified and surprised the German Army under von Bülow with its level of resistance. Nonetheless, German heavy artillery was able to demolish the main forts within a few days. Following the fall of Liège, most of the Belgian field army retreated to Antwerp, leaving the garrison of Namur isolated, with the Belgian capital, Brussels, falling to the Germans on August 20. Although the German army bypassed Antwerp, it remained a threat to their flank. Another siege followed at Namur, lasting from about August 20-23.

For their part, the French had five armies deployed on their borders. The pre-war French offensive plan, Plan XVII, intended to capture Alsace-Lorraine following the outbreak of hostilities. On August 7 the VII Corps attacked Alsace with the objective to capture Mulhouse and Colmar. The main offensive was launched on August 14 with 1st and 2nd Armies attacking toward Sarrebourg-Morhange in Lorraine. In keeping with the Schlieffen Plan, the Germans withdrew slowly while inflicting severe losses upon the French. The French advanced the 3rd and 4th Armies toward the Saar River and attempted to capture Saarburg, attacking Briey and Neufchateau, before being driven back. The French VII Corps captured Mulhouse after a brief engagement on August 7, but German reserve forces engaged them in the Battle of Mulhouse and forced a French retreat.

Battle of the Frontiers

The German Army swept through Belgium, executing civilians and razing villages. The application of “collective responsibility” against a civilian population further galvanized the allies, and newspapers condemned the German invasion and the army’s violence against civilians and property, together called the “Rape of Belgium.” After marching through Belgium, Luxembourg, and the Ardennes, the German Army advanced in the latter half of August into northern France, where they met the French Army under Joseph Joffre and the initial six divisions of the British Expeditionary Force under Sir John French. A series of engagements known as the Battle of the Frontiers ensued, which included the Battle of Charleroi and the Battle of Mons. In the former battle the French Fifth Army was almost destroyed by the German 2nd and 3rd Armies and the latter delayed the German advance by a day. A general Allied retreat followed, resulting in more clashes at the Battle of Le Cateau, the Siege of Maubeuge, and the Battle of St. Quentin (also called the First Battle of Guise).

First Battle of the Marne

The German Army came within 43 miles of Paris but at the First Battle of the Marne (September 6-12), French and British troops were able to force a German retreat by exploiting a gap that appeared between the 1st and 2nd Armies, ending the German advance into France. The German Army retreated north of the Aisne River, establishing the beginnings of a static western front that would last for the next three years. Following this German retirement, the opposing forces made reciprocal outflanking maneuvers known as the Race for the Sea and quickly extended their trench systems from the Swiss frontier to the North Sea. The territory occupied by Germany held 64 percent of French pig-iron production, 24 percent of its steel manufacturing, and 40 percent of the coal industry, dealing a serious blow to French industry.

Laying Trenches and the First Battle of Ypres

On the Entente side (those countries opposing the German alliance), the final lines were occupied by the armies of the Allied countries, with each nation defending a part of the front. From the coast in the north, the primary forces were from Belgium, the British Empire, and France. Following the Battle of the Yser in October, the Belgian army controlled a 22-mile length of West Flanders along the coast known as the Yser Front, along the Yser river and the Yperlee canal from Nieuwpoort to Boesinghe. Stationed to the south was the sector of the British Expeditionary Force (BEF).

From October 19 until November 22, the German forces made their final breakthrough attempt of 1914 during the First Battle of Ypres. Heavy casualties were suffered on both sides but no breakthrough occurred. After the battle, Erich von Falkenhayn judged that it was no longer possible for Germany to win the war and on November 18 called for a diplomatic solution, but Chancellor Theobald von Bethmann-Hollweg, Paul von Hindenburg and Erich Ludendorff disagreed.

Stabilization of the Western Front WWI: Map of the Western Front and the Race to the Sea, 1914

Trench Warfare

After the German march on Paris was halted at the First Battle of the Marne, both sides dug in along a meandering line of fortified trenches stretching from the North Sea to the Swiss frontier with France. The Western Front settled into a battle of attrition, with a trench line that changed little until 1917.

Trench Warfare in World War I

Trench warfare occurs when a revolution in firepower is not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender holds the advantage. Military tactics developed before World War I failed to keep pace with advances in technology and became obsolete. These advances had allowed the creation of strong defensive systems, which out-of-date military tactics could not break through for most of the war. Barbed wire was a significant hindrance to massed infantry advances, while artillery vastly more lethal than in the 1870s, coupled with machine guns, made crossing open ground extremely difficult. Commanders on both sides failed to develop tactics for breaching entrenched positions without heavy casualties. In time, however, technology began to produce new offensive weapons, such as gas warfare and the tank.

On the Western Front in 1914–18, both sides constructed elaborate trench and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, and other obstacles. The area between opposing trench lines (known as “no man’s land”) was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.

Just after the First Battle of the Marne (September 5-12, 1914), Entente and German forces repeatedly attempted maneuvering to the north in an effort to outflank each other, a strategy that became known as the “Race to the Sea.” When these outflanking efforts failed, the opposing forces soon found themselves facing an uninterrupted line of entrenched positions from Lorraine to Belgium’s coast Britain. France sought to take the offensive while Germany defended the occupied territories. Consequently, German trenches were much better constructed than those of their enemy; Anglo-French trenches were only intended to be “temporary” before their forces broke through the German defenses.

Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on March 21, 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals to be decided by attrition. The small, improvised trenches of the first few months grew deeper and more complex, gradually becoming vast areas of interlocking defensive works. They resisted both artillery bombardment and mass infantry assault. Shell-proof dugouts became a high priority. Frontal assaults and their associated casualties became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker’s massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side able to commit the last reserves to the Western Front.

Neither side delivered a decisive blow for the next two years. Throughout 1915–17, the British Empire and France suffered more casualties than Germany because of the strategic and tactical stances chosen by the sides. Strategically, while the Germans only mounted one major offensive, the Allies made several attempts to break through the German lines.

In February 1916 the Germans attacked the French defensive positions at Verdun. Lasting until December 1916, the battle saw initial German gains before French counter-attacks returned them near their starting point. Casualties were greater for the French, but the Germans bled heavily as well, with anywhere from 700,000 to 975,000 casualties suffered between the two combatants. Verdun became a symbol of French determination and self-sacrifice.

The Battle of the Somme was an Anglo-French offensive of July to November 1916. The opening of this offensive (July 1, 1916) saw the British Army endure the bloodiest day in its history, suffering 57,470 casualties, including 19,240 dead, on the first day alone. The entire Somme offensive cost the British Army some 420,000 casualties. The French suffered another estimated 200,000 casualties and the Germans an estimated 500,000.

The last large-scale offensive of this period was a British attack (with French support) at Passchendaele (July–November 1917). This offensive opened with great promise for the Allies before bogging down in the October mud. Casualties, though disputed, were roughly equal at some 200,000–400,000 per side.

These years of trench warfare in the West saw no major exchanges of territory and, as a result, are often thought of as static and unchanging. However, throughout this period, British, French, and German tactics constantly evolved to meet new battlefield challenges.

Trench Warfare: Trenches of the 11th Cheshire Regiment at Ovillers-la-Boisselle, on the Somme, July 1916. One sentry keeps watch while the others sleep. Photo by Ernest Brooks.

Development of Advanced Weaponry

Both sides tried to break the trench stalemate using scientific and technological advances. On April 22, 1915, at the Second Battle of Ypres, the Germans (violating the Hague Convention) used chlorine gas for the first time on the Western Front. After a two-day bombardment, the Germans released a cloud of 171 tons of chlorine gas onto the battlefield. Though primarily a powerful irritant, it can asphyxiate in high concentrations or prolonged exposure. The gas crept across no man’s land and drifted into the French trenches. The green-yellow cloud killed some defenders and those in the rear fled in panic, creating an undefended 3.7 mile gap in the Allied line. The Germans were unprepared for the level of their success and lacked sufficient reserves to exploit the opening. Canadian troops on the right drew back their left flank and repelled the German advance.

The success of this attack would not be repeated, as the Allies countered by introducing gas masks and other countermeasures. The British retaliated, developing their own chlorine gas and using it at the Battle of Loos in September 1915. Fickle winds and inexperience led to more British casualties from the gas than German. Several types of gas soon became widely used by both sides, and though it never proved a decisive, battle-winning weapon, poison gas became one of the most-feared and best-remembered horrors of the war. French, British, and German forces all escalated the use of gas attacks through the rest of the war, developing the more deadly phosgene gas in 1915, then the infamous mustard gas in 1917, which could linger for days and kill slowly and painfully. Countermeasures also improved and the stalemate continued.

Tanks were developed by Britain and France, and were first used in combat by the British during the Battle of Flers–Courcelette (part of the Battle of the Somme) on September 15, 1916, with only partial success. However, their effectiveness would grow as the war progressed; the Allies built tanks in large numbers, whilst the Germans employed only a few of their own design supplemented by captured Allied tanks.