On April 6, 1917, Congress declared war and the United States joined the great conflict that had engulfed Europe since the assassination of Austrian Archduke Ferdinand in 1914. The American Expeditionary Forces (AEF) took the better part of a year to train and mobilize and their first major battle did not take place until the following May. The real challenge for the American troops came in September 1918. It was then that the 47-day battle of the Meuse-Argonne began. Encompassing seven weeks, a 25-mile front and more than one million American troops, the Battle of the Argonne Forest averaged 558 deaths per day, a human cost exceeding any America has paid in battle before or since. Despite the carnage and death, a mixed unit (from one machine gun and three infantry battalions) and their commander, Charles Whittlesey, rose to the rank of legend. Eclipsed by more publicized--yet no more deserving--tales of military valor, this final American offensive of the Great War and the heroic tale of the Lost Battalion remained largely obscure in the annals of American history, until now.