On December 16, 1944, the Germans launched the last major offensive of the war, Operation Mist, also known as the Ardennes Offensive and the Battle of the Bulge, an attempt to push the Allied front line west from northern France to northwestern Belgium.
The Battle of the Bulge, so-called because the Germans created a “bulge” around the area of the Ardennes forest in pushing through the American defensive line, was the largest fought on the Western front. The Germans threw 250,000 soldiers into the initial assault, 14 German infantry divisions guarded by five panzer divisions-against a mere 80,000 Americans.
Isolated American units and the thick fog that prevented Allied air cover from discovering German movement, the Germans were able to push the Americans into retreat.
Fighting was particularly fierce at the town of Bastogne, where the 101st Airborne Division and part of the 10th Armored Division were encircled by German forces within the bulge. On December 22, the German commander besieging the town demanded that the Americans surrender or face annihilation.
U.S. Major General Anthony McAuliffe prepared a typed reply that read simply:

To the German Commander:
Nuts!
From the American Commander

The Americans who delivered the message explained to the perplexed Germans that the one-word reply was translatable as “Go to hell!” Heavy fighting continued at Bastogne, but the 101st held on.
The embattled Americans kept up a fierce resistance even after their lines of communication had been broken, buying time for a three-point counteroffensive led by British General Bernard Montgomery and American generals Omar Bradley and George Patton.
Germany’s last major offensive of the war had cost them 120,000 men, 1,600 planes, and 700 tanks. Historian Stephen Ambrose estimated that by battle’s end, “Of the 600,000 GIs involved, almost 20,000 were killed, another 20,000 were captured, and 40,000 were wounded.”
On December 23, the skies finally cleared over the battle areas, and the Allied air forces inflicted heavy damage on German tanks and transport, which were jammed solidly along the main roads. On December 26, Bastogne was relieved by elements of General Patton’s 3rd Army. A major Allied counteroffensive began at the end of December, and by January 21 the Germans had been pushed back to their original line.