When the United States declared war on Germany in April 1917, the tiny US Army did not even have a standing division. A huge national army worthy of the Western Front was quickly enlisted, trained, and then transported to France to fight against the Germans. In September 1918, the American Expeditionary Force, under General John Pershing, began its first full-scale offensive against German forces in Lorraine, in which the US First Army and (eventually) the US Second Army would drive north between the Argonne Forest and the Meuse river towards Sedan. The Meuse-Argonne was excellent defensive terrain, being hilly, steep, heavily wooded, and fortified by the Germans over a three-year period. The offensive began on 26 September, 1918.