In 1944 the Ardennes region of Belgium was the frontier between Nazi Germany and the Allies.

After six months of hard but successful fighting, Allied troops had taken up winter quarters ready for the expected invasion of Germany in spring 1945.

Then, just days before Christmas on December 16th, a quarter of a million German troops launched a shattering offensive through the Ardennes.

The allied troops were taken completely off guard. They thought the war was almost over; only to find themselves engulfed in one of the greatest land battles of the 20th Century.

At first, Hitler's Ardennes Offensive was successful, but nearly two months of fighting left the German Army in ruins.

In this programme scientists and historians investigate why the Battle of the Bulge ended in total defeat for Germany.