The Battle of Huertgen Forest (German: Schlacht im Hürtgenwald) is the name given to the series of fierce battles fought between U.S. and German forces during World War II in the Hürtgen Forest, which became the longest single battle the U.S. Army has ever fought in its history. The battles took place between September 19, 1944, and February 10, 1945, in a corridor of barely 50 square miles (129 km²) east of the Belgian–German border. U.S. commanders’ initial goal was to pin down German forces in the area so as to keep them from reinforcing the front lines further north, between Aachen and the Rur (Roer) River, where the Allies were basically fighting a trench war between a network of fortified towns and villages connected with field fortifications, tank traps, and minefields. A secondary objective may have been to outflank the front line. The Americans' initial objectives were to take Schmidt, clear Monschau, and advance to the Rur. The Germans fiercely defended the area for two reasons: It served as staging area for the Ardennes Offensive (what became the Battle of the Bulge) that was already in preparation, and the mountains commanded access to the Schwammenauel Dam at the head of the Rur Lake (Rurstausee) which, if opened, would flood low-laying areas downstream and deny any crossing of the river. The Allies only recognized this after several heavy setbacks, and the Germans were able to hold the region until they launched their final major, last-ditch offensive on the Western Front, into the Ardennes.