On the morning of December 16, 1944, more than 200,000 German troops and almost 1,000 tanks drove into the Ardennes forest across an 85-mile stretch of the front line, from southern Belgium to the middle of Luxembourg.
The German thrust shredded Allied lines, held by units sent to the Ardennes to rest and reorganize.
Bad weather held Allied airpower in check, and many American troops were caught off guard. The US Army's 106th Infantry division was encircled in hours, and two out of three soldiers were caught or killed.
US forces settled into wholesale retreat, save for a few pockets of soldiers who fought on but were quickly isolated, though they held crucial road junctions.
The Germans pushed a 50-mile bulge into Allied lines on the Western Front. Gen. Dwight Eisenhower saw a chance to break the German war machine, and more than a half-million troops were thrown into battle.
The two armies clashed in driving snow and subzero temperatures. Soldiers often couldn't see more than 10 yards or 20 yards in front of them.
"Both the enemy and the weather could kill you," Pvt. Bart Hagerman of the 17th Airborne said in a PBS documentary. "And the two of them together was a pretty deadly combination."
Casualties mounted for the US, and physical-fitness standards were lowered to pull in more troops. Men suffering from physical or mental wounds were thrown back into the fight.
"It's very hard to forget the expressions on their faces ... a kind of hollow-eyed, lifeless, slack-jawed expression," Ben Kimmelman, a captain in the 28th Infantry, said in the documentary. "It's almost as though they're going to a hopeless doom."
The battle lasted until the end of January 1945, when Allied troops returned to their original lines. Almost a million troops were engaged, and 16,000 Americans were killed, with another 60,000 wounded or captured. German losses were thought to be twice that.
A US Army half-track crossing a temporary bridge over the Ourthe River in the war-torn Belgian city of Houffalize, during the Battle of the Bulge in January 1945.
US soldiers checking for identification on the bodies of US troops shot by the Germans near Malmedy, Belgium, in January 1945.
A dead German soldier, killed during the German counteroffensive in the Belgium-Luxembourg salient, on a street corner in Stavelot, Belgium, on January 2, 1945.
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