The battle of Aachen took place in the Huertgen Forest near Aachen Germany between September and December of 1944. The objective for the allies was to sweep the forest near the Belgian-German border clear of Germans. To protect the flank of the U.S. VII Corps as the Allies advanced toward Germany in September, the U.S. First Army plunged in the fifty-square-mile morass of Huertgen Forest, just inside the Reich.
The operation was inadvisable from the start: the defending Germans considered the area vital to their defense and were determined to hold; moreover, they could destroy dams on the Roer River to the south and the east and flood out any Allied advance in the north. But there was no advance through the forest: First Army was quickly bogged down in the difficult terrain. Worse, a portion of the Germans' Siegried Line (West Wall) lurked half-submerged in the forbidden landscape. The impenetrable forest also neutralized American artillery and air superiority. Incessant snow and rain devastated the attackers. Yet, for more than three months commanders at headquarters in Spa, Belgium, continued to send division after division into these impossible conditions.
The forest was eventually taken at an etreme, and unforseen cost in life, but the Germans delayed the First Army's progress enough to assist preparation for Germany's last counteroffensive in the Ardennes (Battle of the Bulge).
taken from - Wagner, Margaret E, David M. Kennedy, Linda B. Osborne, and Susan Reyburn. The Library of Congress World War Ii Companion. New York: Simon & Schuster, 2007. p. 594-595.