By August 1944, the Allies were advancing across France at breakneck speed, chasing an exhausted and demoralized German army from most of the country. Progress toward the German border began slowing in September after Adolf Hitler reappointed Gerd von Rundstedt to lead all German forces in the West. The highly accomplished field marshal had been sacked weeks earlier by Hitler for failing to prevent the Allied breakout in Normandy, but with his return the German lines finally began to stabilize.

The Allied advance was also hindered by a supply crisis. As their armor and infantry moved farther away from the landing beaches in Normandy, thinning supply lines led to acute shortages of fuel and ammunition.

The Germans, meanwhile, were feverishly building up their defenses along the West Wall (known to the Allies as the Siegfried Line) – a stout network of fortifications and obstacles along the length of the German-Franco border. Certain that heavy casualties would ensue from a direct assault, General Dwight Eisenhower, the Supreme Allied Commander, approved a daring plan put forward by British Field Marshal Bernard Montgomery to attack the Germans in the north, circumventing the West Wall.

Under Operation Market-Garden, 35,000 British and American paratroopers would land behind the German lines in occupied Holland and seize a series of bridges leading north to the city of Arnhem. Further south, a powerful corps of British armor would smash through the German lines along the Belgian-Dutch border, then drive north across Holland, linking up with the airborne troops at each bridge. After reaching the last bridge at Arnhem, the armor would cross the Lower Rhine River into Germany and sweep into the Ruhr Valley, the country’s industrial heartland.

It was hoped Market-Garden would finish the war by Christmas. Instead, the operation ended in spectacular failure after British paratroopers landed in the midst of an SS panzer corps sent to the Arnhem area for rest and refitting. Other planning errors, bad weather, and communication failures added to the Allies’ woes. With an entire British airborne division nearly annihilated, and no hope of capturing the final bridge in Arnhem, the operation was called off.

Further setbacks followed. In October, the US First Army crossed into Germany, reaching the ancient city of Aachen, but Hitler ordered the enclave held at all costs. It would fall, but not before more than 10,000 Americans were killed or wounded. Equally ill-fated were efforts to clear out the Huertgen Forest, an immense patch of woods along the German-Belgian border. Fighting across dense, forbidding terrain that nullified Allied advantages in air power and armor, a relatively small number of Germans fought several US infantry divisions to a three-month standstill, inflicting another 31,000 casualties on the Americans.

As winter settled in, Allied armies were exhausted. Many of the troops had been in continuous action since D-Day and were desperate for rest before a final, concerted push into Germany. Hitler had other plans.