This map from the 12th United States Infantry Army shows US, British, and German troop positions on the first day of the Battle of the Bulge. One of the the fiercest battles of World War II, the engagement started as an offensive campaign by Nazi Germany. Taking place in the Ardennes Forest in Wallonia, Belgium, the fighting raged from December 16th, 1944 until January 25th, 1945. Though it was one of the worst battles for the United States in terms of casualties, the Battle of the Bulge (also known as the Ardennes Offensive) resulted in Germany's defeat, and marked a turning point in the war for the Allies.
The 12th United States Army Group was the biggest and most dominating US Army formation at that point. They made up the right wing of Allied lines at Normandy, and later formed the center of the Allied forces on the Western Front. By the end of the war in Europe, the Twelfth Army Group had over 1.3 million among its ranks.
Map includes the following text:
12th Army Group Outline Maps 1:1,000,000
SITUATION - 1200 HRS - 16 DECEMBER 1944 - TWELFTH ARMY GROUP