When the United States declared war against Germany in April 1917, its most recent expeditionary military efforts had involved sending 10,000 men into Mexico in 1916 and 1917, maintaining a combat force of approximately 25,000 men in the Philippines from 1899 to 1902, and deploying 17,000 men to fight the Spanish in Cuba in 1898. Prior to that, during the Mexican-American War (1846-1848) the combined American invasion forces never exceeded 20,000. Simply put, the United States had never attempted anything approaching what it did in Europe between mid-1917 and late 1918. The dispatch of the American Expeditionary Forces (AEF) to the Western Front constituted the greatest, most intense military effort in the nation’s history to date. Though the Civil War (1861-1865) lasted longer, America’s participation in the Great War led to the creation of the nation’s largest army to date (nearly 4 million men under arms); the shipping of over 2 million of them to Europe; and the waging of the nation’s largest, longest, and most deadly battles. In sum, the AEF represented the first massive projection of American military power into Europe, and it dwarfed all previous military expeditions.

The American combat experience was fraught with tension, both with elements of the War Department at home and with the Allied powers in Europe. It was also characterized by battles and campaigns that showed the AEF's hurried creation, operational inexperience, and anachronistic initial combat doctrine. The AEF nonetheless played a critical role in the defeat of Germany. When the United States entered the war in mid-1917, all the major forces of both sides were showing the material and moral strains of three years of total war. The Allies suffered a wave of calamitous events between mid-1917 and mid-1918. Two revolutions led to Russia’s withdrawal from the war. France’s disastrous Nivelle offensive was followed by mutinies in most of its combat regiments, which General Philippe Pétain (1856-1951) squashed, in part by telling the men he would henceforth wait for the Americans and the tanks. The British suffered horrific casualties at Passchendaele/Third Ypres and Italy a disaster at Caporetto. The tremendous initial successes of the German U-Boat campaign in 1917, which threatened to destroy the British war effort, and then the shockingly successful German offensives in the spring of 1918 further contributed to the dire situation. Given these events, it is hard to imagine an Allied victory in 1918, or perhaps even in 1919, without the massive reinforcement of fresh and aggressive, though inexperienced, American forces on the Western Front.

Building the AEF: Mobilization, Organization, Training

When the United States declared war its Regular Army was less than 135,000 strong, and its National Guard (the modernized militia system run primarily by the individual American states) was not much larger.[1] The U.S. Army did not have organized combat divisions and was scattered throughout the world in regiments and companies. It possessed stocks of just 285,000 rifles, 550 artillery pieces, fifty-five aircraft (all obsolete or obsolescent), and no tanks.[2]

Aware of this, France and Britain sent high level missions to the US. Led by Marshal Joseph Joffre (1852-1931) and Rene Viviani (1863-1925) on behalf of the French, and Arthur Balfour (1848-1930) and General Tom Bridges (1871-1939) on behalf of the British, these delegations were sent to advise the American government of their countries’ needs.

These missions initially suggested that the United States immediately send men straight into their own respective armies in order to make the quickest impact on the Western Front. Joffre, however, sensed the negative reaction this approach was having and quickly changed course. Thus began one of the most significant and recurring issues of the American war effort - the amalgamation controversy - in which the Allies repeatedly pressed for American soldiers or units to be directly incorporated into British and French field armies. Major General Tasker H. Bliss (1853-1930), then the Assistant Chief of Staff of the U.S. Army but soon to be appointed to the new Supreme War Council, advised the Secretary of War to reject these initial pleas, noting that such a policy would cause heavy American casualties without necessarily winning the war decisively, and could lead to a final result in which the war ended without the US getting credit for the victory.[3] Still, European efforts to amalgamate American military personnel and units, in varying forms, continued right up to the final offensives in late 1918. In rejecting amalgamation, the American administration committed itself to creating the first truly modern, industrial, independent army in its history.

Only after the U.S. government finalized arrangements for a massive draft in May 1917 did it send a small contingent to Europe, led by General John J. Pershing (1860-1948). Pershing was neither the most senior nor the most famous officer in the army, but he was politically reliable and had recent command experience chasing Pancho Villa (1878-1923), one of the most prominent Mexican Revolutionary generals, from the Mexican border. Pershing’s small command and staff element, soon followed by units of the 1st Division, landed in France in late June. Pershing and his staff began writing plans regarding the size, scope, composition, and organization of the AEF, while the men of the 1st Division began training for modern war under the tutelage of the French Army. Armed with crystal clear instructions from Secretary of War Newton Baker (1871-1937) that the AEF Commander-in-Chief keep in mind “the underlying idea” that the AEF was a “separate and distinct component of the allied forces, the identity of which much be preserved,” Pershing strongly resisted any Allied scheme that hinted at permanent amalgamation.[4] After consulting senior Allied political and military leaders and studying the situation on the Western Front, he began developing a series of plans that first called for 1 million men, then for sixty-six full divisions (plus supporting personnel), then eighty, and finally for 100 divisions, all in line with his vision of creating a massive American force capable of delivering an unstoppable war-winning campaign in 1919.[5] Yet by the end of 1917, with the draft in full swing and the War Department organizing and training men and units throughout the United States, parts of just four divisions were abroad training with the French Army and getting exposure to modern warfare by spending time in the front lines of quiet sectors.

AEF divisions officially were categorized as Regular, National Guard, or National Army (draftee), but in reality all were led by professional senior officers and filled with volunteers or draftees. Regardless of the designation, all three were organized in the same way - as huge divisions composed of two 8,000 man brigades of infantry (each with two regiments, each regiment with three battalions, and each battalion with four 250-man companies). When the three regiments of the organic artillery brigade are included, as well as the combat engineers, supply troops, and others, the AEF division came to over 28,000 men, about twice the size of full-strength British, French, or German divisions. Some historians have suggested that Pershing created the large division because he suspected he did not have a sufficient number of senior officers ready to serve as division commanders. The official reason given was that the larger AEF division was designed to engage in the hard slugging and heavy slogging of the Western Front without needing to be replaced as often. Pershing hoped his big units would have the fighting power to batter their way through the tough German lines and retain the fighting strength to carry the fight out into the open.

In order to help this unorthodox organization, Pershing and his key staff officers at General Headquarters (GHQ) promulgated what was by 1917 a rather unique, though somewhat ill-defined, combat doctrine. Commonly called “open warfare,” official AEF doctrine was based on prewar US Army regulations, and stressed maneuver and marksmanship over frontal attacks and firepower. At its best, when used by experienced troops and supported by massive amounts of artillery, “open warfare” shared some similarities with the infiltration tactics used by German storm-troopers. At its worst, when inexperienced officers took it at face value and attempted attacks with unproven, poorly trained, and weakly supported lines of “self-reliant infantry,” it led to horrific casualties.[6] In the end, the best American units learned enough of the essential “trench warfare” skills and techniques from their French and British tutors, as well as from their own harsh experiences, to be able to achieve some level of operational success. American officers also gained exposure to the Allies’ best practices from European officers who served in the many technical and staff schools the AEF established throughout France. Although Pershing feared his officers would absorb conservative, trench warfare attitudes from the Allied trainers and instructors, the evidence suggests that the real harm of these schools was the personnel turbulence they imposed on AEF divisions, whose key commanders and staff officers were often absent during crucial periods of unit integration and training.[7]

Beyond doctrine, American units also had to support their operations with weaponry and equipment provided by the Allies, including the famous French 75mm field gun, the British Stokes mortar, the Renault light tank, and the Nieuport and Spad aircraft. American industry was painfully slow to provide the guns, tanks, aircraft, and other key weapons required for modern war. The entire American mobilization plan was based on building a massive American force for a decisive offensive in 1919, rather than fielding the quickest medium-sized force possible. The personnel and equipment mobilization plans, as well as the unit training programs in the United States and abroad, followed this principle. Unfortunately for the AEF, events in Europe conspired to bring about a series of crises in 1918 that threw all American plans and programs into disarray. Germany’s five spring offensives from March to July caused such a state of emergency that the Allies pleaded with Pershing to alter his development plans in significant ways. First, they convinced him to agree to ship only infantry and machine-gun units from the United States, as opposed to a more balanced transport schedule that would bring complete divisions, corps and army level staff assets, as well as other essential support personnel and equipment. Second, they persuaded Pershing to allow some immediate amalgamation to help stop the German advances. American divisions, brigades, and occasionally even regiments were sent - temporarily in the mind of the AEF commander - to serve in Allied corps and armies. Third, Pershing allowed American units who had not completed the methodical training program designed by GHQ either to go into the front lines of quiet sectors (thus releasing more experienced Allied units for duty closer to the action), or in the cases of a few of the better trained divisions such as the 1st, 2nd, and 3rd Divisions, to move directly into the active combat sectors. These divisions were supposed to first help stop the German offensives and then start the important counterattacks that proved to be the turning point in the war on the Western Front. This change of policy continued for the remainder of the war, culminating in Pershing’s willingness to use partially trained men and units in significant ways during Marshal Ferdinand Foch’s (1851-1929) general fall offensive that overwhelmed the German army and ended the war in 1918.

All subsequent activities by the AEF were affected by these important decisions. Despite Pershing’s supposed inflexibility, there is no doubt that the AEF’s future performance suffered because Pershing agreed to respond to the 1918 emergencies and opportunities in the way he did. In retrospect, Pershing was clearly more flexible than many of his contemporaries gave him credit for being, especially in light of his instructions from Secretary Baker. The darker side of his flexibility (as well as other weaknesses of the American mobilization effort) was that in numerous instances American units and individual soldiers were thrown into battle before GHQ had intended, and more controversially, before they were ready. Whether that sacrifice was warranted by the crises and opportunities of 1918 is worth debating, but it was a crucial decision that is essential for all students of the AEF and the Western Front to understand.

Combat on the Western Front

The AEF initially played a valuable, but passive, role towards Allied victory, as the existence of even a few American soldiers in Europe, with the promise of millions more to follow - arriving at the rate of 5,000 to 10,000 a day in the spring and summer of 1918 - changed the war for the Germans.[8] The clock was ticking, and unless the Germans could win the war before the AEF grew to substantial size, they had no hope of victory. And in fact, the large and active, though inexperienced, AEF contributed significantly to an eventual Allied victory but especially to the relatively decisive one accomplished in 1918. Meaningful American involvement on the Western Front lasted for about a year, beginning in January 1918 when the 1st Division took command of its own sector of the front. Every AEF division that entered the lines either released experienced Allied divisions from quiet sectors for service in more active sectors, or helped form a large and growing reserve that served as both insurance against decisive German victories and as an investment in sustaining Allied counterattacks. By mid-October 1918, the AEF was responsible for 101 miles of the Western Front, the French Army for 244, and the British Expeditionary Force (BEF) for eighty-three.[9] This statistic does not correspond to the respective armies’ contributions toward victory, but it is an important element of the story.


The more active AEF contribution to Allied victory began in May 1918, when the 1st Division entered the front lines west of Montdidier as part of a French corps and army. In late May it planned and conducted an attack on new German positions near the town of Cantigny. Although aided by additional French artillery and tank units, the battle plan and most troops were American. This first American attack of the war, though small, was quite successful. Perhaps even more impressive than planning and executing the initial assault was the tenacity and stamina shown by the American soldiers; they held their new positions at all costs, even when they came under strong, numerous, and costly counterattacks, and when the French withdrew most of their supporting artillery. Cantigny thus demonstrated that the American forces were not just numerous and fresh, but tough and determined. Although many American units demonstrated their inexperience in future attacks, instances of German troops pushing back American units were extraordinarily rare throughout 1918.[10]

Belleau Wood and Vaux

The 1st Division lost most of its supporting French artillery after the successful Cantigny assault because in late May the Germans smashed through the French lines to the south along the Chemin des Dames. The attack advanced so far, so fast, that French citizens began to flee Paris for the first time since 1914. Initially scheduled to relieve the 1st Division at Cantigny, Pershing instead released his 2nd Division (uniquely comprised of one brigade of US Marines and one brigade of soldiers) to the French army to help stop the enemy advance. The 2nd Division set up in a long, thin line blocking the road to Paris in that sector. Although the German attacks were just about spent, broken French units straggled through the American lines insisting “la guerre est fini![11]

As with the 1st Division at Cantigny, the 2nd Division established its lines as part of a French corps in a French field army. Like its sister division to the north, it did not stay on the defensive long. On 6 June it executed its first attack of the war, the seizure of a small area of trees known as Belleau Wood. The first attack was poorly planned, weakly supported, and not well executed. The Marines suffered more casualties on that day than they would on any single day until the battle of Tarawa in World War II. Subsequent assaults yielded better results, and soon, when the German high command realized that an American division was making the attacks, they ordered furious counterattacks. A terrible grudge-match was underway. After three weeks and thousands of casualties on both sides, the Marine Brigade emerged victorious, and the French ceremoniously renamed the wood “La Bois de la Brigade de Marine.” Though the Marines did not initially fight with great expertise, they improved throughout the battle, and their very presence, not to mention their aggressiveness, gave the French army a needed boost of morale.[12] Within a week of the Marines’ success, the division’s brigade of soldiers proved they had learned quite a bit from watching the Marines slug it out at Belleau Wood. They meticulously planned and brilliantly conducted a relatively small but exquisite assault on the town of Vaux nearby. It showed that on a tactical level, the staff and units of at least one AEF division could expertly plan and execute small, set-piece attacks.[13]


Near Belleau Wood and Vaux the 2nd Division pushed back the German lines after a German offensive had stalled. At Chateau-Thierry the 3rd Division played a very real and impressive role in helping to stop both the third and the fifth German offensives. On the last day of May, a motorized machine-gun battalion, soon followed by other divisional infantry units, arrived in time to play an important role in helping to stop German forces from crossing the Marne. Six weeks later, the division performed superbly when the Germans unleashed their fifth and final offensive of the year. Fully under French corps and army command like the 1st and 2nd Divisions before it, the 3rd Division tenaciously held its ground while French units on its flanks gave way. Its dogged defense earned the division the nickname it still carries to this day, “The Rock of the Marne.”[14]

Hamel and Subsequent Operations with the BEF

Fifty miles north of the American successes at Belleau Wood and Chateau-Thierry, the 33rd Division performed a small but valuable service by taking part in the Australian attack at Hamel on 4 July. In total, nine AEF divisions trained with the British, four engaged in combat operations with the British Expeditionary Forces (BEF) (including units from the 33rd Division, which took part in the hugely successful Amiens attack of 8-9 August), and two of them (the 27th and 30th Divisions) served exclusively with the BEF as part of the American II Corps in the Ypres and Somme sectors. These two divisions took part in serious fighting along the Hindenburg Line in August and September 1918, though they had to attack without their own divisional artillery brigades, a result of the accelerated shipping of infantry and machine-gun units in the spring of 1918.[15] Contemporary Allied officers criticized the performance of these units, but some modern historians have concluded that their British and Australian commanders used them poorly, making these units less culpable for their failures than the British and Australian senior army and corps commanders.[16]

The Aisne-Marne Counteroffensive

Within just three days of the failure of the fifth German offensive on 15 July 1918, the French army conducted a massive counterattack in the area of the Aisne and Marne valleys that was so successful that it completely erased all Germany’s gains from its May offensive. The attack, begun on 18 July, proved to be the turning point of the war. From that point forward, the Allies moved continuously forward, and the Germans backward. Without the involvement of 300,000 Americans it is almost impossible to imagine that this attack could have been carried off at all, and almost certain that it would not have been as strikingly successful as it was. In fact, Marshal Pétain admitted as much after the war.[17] Of particular note, the 1st and 2nd Divisions served as the spearhead of the attack as part of a French corps in General Charles Mangin’s (1866-1925) French Tenth Army. Despite tremendous logistical difficulties, the American units attacked on time and drove forward faster and farther than the French units on their flanks, ultimately forcing the Germans in the massive salient to the south to initiate a slow, but steady withdrawal.[18] But the cost was high. Fighting in open conditions for the first time, American tactics and coordination were poor, and the two divisions suffered over 12,000 casualties in just a few days of fighting. Ultimately nine American divisions took part in this key campaign (some going into the line more than once), and most of them suffered severe casualties as they learned hard lessons while fighting in more open conditions.

The St. Mihiel Offensive

On 10 August Pershing’s vision for an independent American force took a monumental step forward when he took command of the American First Army (while still retaining his role as Commander-in-Chief of the AEF). Pershing had long expected that the Americans would have to take over the lines along the southeastern portion of the Western Front - thus allowing the British to remain in front of the channel ports, and the French to guard Paris. The First Army therefore immediately focused its attention on eliminating the large salient jutting out of the German lines between Verdun and Toul. Pershing saw the attack on the salient as just the first phase of a deeper drive toward Metz, the opening gambit of the war-winning campaign envisioned by the American leadership. However, just two weeks before the massive attack was to begin, Foch asked Pershing to curtail or eliminate it, and to divide his American forces up between French armies along a different portion of the front. After severe disagreement, Pershing and Foch agreed to have the Americans destroy the St. Mihiel salient, and then immediately move the First Army forty-three miles to the northwest to take over a completely different portion of the front lines, between the Argonne Forest and the Meuse River. There it would join the other Allied armies on the Western Front in conducting a simultaneous, general offensive along the entire line.

It was a fateful decision, one that forced the AEF to attempt a nearly impossible logistical and operational task. Nonetheless, the St. Mihiel Offensive, which began on 12 September, was a stunning success. The largest battle in American history to date, the First Army included 550,000 Americans and 110,000 Frenchmen in four different corps, as well as the largest collection of airpower of the war - over 1,400 French, American, British, and Italian aircraft. Aided by having caught the Germans in the middle of defensive adjustments, the First Army overwhelmed the defenders within just two days. U.S. forces took all their objectives, freed over 200 square miles of French territory, and captured over 15,000 Germans and 450 artillery pieces at the cost of about 7,000 casualties.[19] The more experienced American divisions began to show significant improvement. The Pershing-Foch agreement did not hurt the effort at St. Mihiel (though it did prevent it from continuing), but it did create serious problems, if not outright failure, for the AEF in the subsequent and more massive offensive to be started less than two weeks later in the Meuse-Argonne sector.

The Meuse-Argonne Offensive

Between the close of the St. Mihiel offensive on 16 September and the start of the Meuse-Argonne offensive just ten days later, American staff officers had to replace the 220,000 French troops in the sector with 600,000 Americans. Colonel George C. Marshall (1880-1859), a young staff officer who would become the Chief of Staff of the U.S. Army during World War II, deserves much of the credit for getting the First Army in place to initiate the offensive on time.[20] From its start on 26 September until the armistice, the Meuse-Argonne Offensive ground its way forward, at times chewing up AEF units like the Somme offensive did to the BEF two years before. The initial advance began well, with some units driving more than five miles in the first two days. But then resistance stiffened, and the advance slowed down. Some units became seriously disorganized, and sooner or later each of the nine initial divisions needed to be replaced.

The terrain was ideally suited for defense, and the Germans had turned their multiple defensive positions into veritable fortresses. Pershing replaced worn out divisions and ordered his corps commanders to continue pushing forward. The brutal fighting produced some of the most famous events of the war, such as the saga of “the Lost Battalion” - a battalion sized group of the 77th Division that was cut off behind German lines in the Argonne Forest for six days, but tenaciously resisted German counterattacks until rescued. Also in the Argonne, Sgt. Alvin York (1887-1964), a pacifist draftee from Tennessee, achieved fame by killing at least fifteen German soldiers and then gathering up 132 German prisoners, all in the same firefight.

By 15 October, the First Army was desperately in need of rest and reorganization. Up until this point Pershing had been serving as commander of the entire AEF while also commanding a field army (with a front of sixty miles) that was waging the largest battle in American history. He now finally yielded command of the First Army to General Hunter Liggett (1875-1935), his most experienced corps commander, and created the Second Army near St. Mihiel, commanded by General Robert Bullard (1861-1947). Liggett promptly called a halt to the increasingly disjointed general attacks, straightened out his front lines, replaced worn out units with fresher ones, and allowed the army to make more methodical arrangements for a resumption of the offensive on 1 November. This attack, which incorporated important tactical and technical innovations, finally broke the German lines and threw the defenders into a rapid retreat across the Meuse. When the armistice ended the fighting, seven AEF divisions were across the Meuse, ready to drive the Germans back even further should the fighting resume. Over the course of the forty-seven day offensive, more than one million Americans served in the First Army (as did more than 100,000 Frenchmen); in this offensive alone the First Army lost about 117,000 men. The army advanced nearly forty miles, inflicted approximately 100,000 casualties on the German Army, and captured 26,000 German soldiers, 874 artillery pieces, and 3,000 machine guns.[21] It remains the largest and deadliest battle in American history.

Significant Reinforcement on other Fronts

In addition to the two divisions of the American II Corps that fought with the BEF in the fall of 1918, other American units continued to fight in the French and British armies during the remaining months of the war. Of note, the 2nd Division successfully accomplished an extraordinary assault of Blanc Mont Ridge as part of the French Fourth Army in the Champaign sector in early October, and after becoming exhausted in follow-up attacks, was replaced by the rookie 36th Division, which continued the advance for many days. Pershing also allowed two other divisions, the 37th and 91st, to join the French and Belgian forces near Ypres in late October. Four African American regiments fought exclusively and, by all accounts very well, with the French Army during 1918. An augmented regiment was sent to Italy in the summer of 1918 to boost morale in the Italian army. Finally, three battalions of infantry, along with a contingent of engineers, joined the British-led Allied intervention in northern Russia (near Archangel) from mid-1918 until August of 1919, while two reinforced regiments from the Philippines deployed to Siberia from mid-1918 until April 1920.

Summary of AEF combat contributions

America was a belligerent for just the last eighteen months of the war, and an active combatant on the Western Front for only the last six months. Yet, the role of the AEF was significant. The entry of the United States into the war stabilized the French army after the mutinies of 1917 and forced the Germans to roll the dice in the spring offensives of 1918, as they knew that by 1919 the Americans would have a truly decisive force in France. The Americans helped stop those terrifying offensives (both by holding quiet sections of the front, and then by helping to plug the gaps during the third and fifth offensives). U.S. forces gave the Allies the weight of manpower needed to quickly counterattack in July during the Second Marne campaign, freed the St. Mihiel salient with surprising ease, and played a significant role in the general Allied offensive that pushed the Germans back along the entire front from late September 1918 until 11 November 1918. The AEF was not the most tactically or logistically competent force on the Western Front in 1918. Due to a host of factors, the divisions of the AEF probably varied more in quality than the divisions of any other nation. Units that fought early and often, such as the 1st, 2nd, 32nd, and 42nd divisions, became surprisingly effective. Others, such as the 35th, 37th, and 77th, never achieved anything close to the same level of competence due to the abbreviated training regimen, poor leadership at many levels, and insufficient time at the front to learn and improve. And yet, the combination of massive numbers of fresh troops and the demonstrated willingness to fight common to all AEF divisions played a significant role both in ensuring an eventual Allied victory, and in making Allied victory in 1918 even possible.

Mark E. Grotelueschen, United States Air Force Academy

Section Editor: Edward G. Lengel