How the American Expeditionary Forces transformed from a minor force into a decisive power.

History · Published 3 October 2026 Swipe more like this →

In short: In 1917, the American Expeditionary Forces arrived in Europe as an untested military entity. By the end of the war, over a million Americans were fighting on the Western Front. This massive mobilization required unprecedented logistical feats, fundamentally shifting the balance of power in the final months of the conflict.

Established in 1917 by Secretary of War Newton D. Baker, the American Expeditionary Forces (AEF) were placed under the command of General John J. Pershing. Initially, the force faced significant skepticism from Allied leaders who doubted the capabilities of an army lacking experience in large-scale warfare. Pershing, however, remained steadfast in his insistence that American troops be well-trained before deployment and, crucially, that they fight under their own command rather than serving as mere replacements to fill gaps in depleted British and French units.

The logistical challenge of transporting and supplying these troops was immense. With transport ships in short supply, the U.S. Army utilized passenger liners and seized German vessels to move soldiers across the Atlantic. Once in France, the effort required massive infrastructure development; American engineers constructed 82 new ship berths, nearly 1,000 miles of standard-gauge railway tracks, and over 100,000 miles of communication lines. By May 1918, the scale of this mobilization was clear, with more than one million American troops stationed in France.

The AEF’s combat evolution culminated in late 1918. The Battle of Saint-Mihiel in September marked the first major U.S.-led offensive, proving the effectiveness of American command. This was followed by the Meuse-Argonne Offensive, a series of final, grueling confrontations on the Western Front. While the AEF relied heavily on French and British equipment—including French artillery and tanks—the sheer volume of American participation contributed significantly to the eventual armistice. The records of the General Headquarters, now held at the Truman Library, document this transformation through daily intelligence summaries, air patrol reports, and war diaries that track the rapid shift from small-scale training to decisive, large-scale military operations.

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