The 91st Infantry Division was a National Army Division created prior to World War I. Based at Camp Lewis, Washington, it was composed of draftees from the northwestern United States. Following a train up that lasted less than one year, this division departed for Europe in June 1918. In France, the 91st Division conducted additional training, but the AEF pushed it to the front lines before it was completed. In its first combat experience, the 91st Division fought on the front lines of the Meuse-Argonne. In the first days of this battle, the 91st Division, although inexperienced, gained more ground than any other American division. However, it paid a heavy price in terms of American lives. The AEF subsequently assigned the division to work under French command in the battle of Ypres-Lys in Belgium. This book examines the division leadership's ability to execute necessary warfighting functions and combined arms operations in the challenging environment of 1917-1918. The division was tested and accomplished a significant amount, but it also suffered many deficiencies and was forced to learn hard lessons in combat.