Infantry Drill Regulations, United States Army, 1911: Corrected to April 15, 1917 (changes Nos. 1 to 19)

This is the book American soldiers carried into the First World War. Originally published in 1911 and corrected through April 1917, nineteen updates that capture a military on the cusp of transformation, these are the regulations that governed how soldiers moved, fought, and followed orders in the age before mechanized warfare reshaped everything. The manual systematically covers everything from individual soldier training (the School of the Soldier) to company-level formations and the chain of command. It is not theory but prescription: exactly how a squad should deploy, how a company should advance, how orders should be given and obeyed. For military historians, this is a primary source that shows doctrine just before the trenches and tanks made it obsolete. For anyone curious about how armies actually function at the institutional level, it offers a window into a military culture of discipline, precision, and hierarchy that sent millions of men to fight in Europe.