Book excerpt: Upon the entry of the United States into World War I, the American Expeditionary Forces (AEF) were created by the War Department on short notice from existing units, filled up with men from the training camps and deployed with only their personal weapons and equipment. The US Army was not prepared for combat in France, and the remarkable achievement of the AEF's commanding officer, John J Pershing, was the creation of an American field army, built and nurtured from the bottom up. This book details the organizational structure, training and doctrine of the AEF and illustrates how it came to make a significant contribution to Allied victory in World War I.