The Germans discover the technique of air bursting their mortars with deadly effect, as American Arnold Whittaker found out: 'The first night I was caught in tree bursts... they would hit the trees and explode and then come down like hot ragged metal and hit you... a 19-year-old kid... after one day I'm a veteran.'

Losses were high. Soldiers like 18-year-old Gil Nelson had never been in battle before. He arrived on the frontline straight from training. His memories are still vivid: 'So much mayhem, the sound, the... sight of blood, the death of people... the screams.'

By now the Allies were up against a German counter-offensive at the Battle of the Bulge. Frank Camm, a US army officer, had to take out German bunkers.

'At first we'd take a flame-thrower if there were any infantry there to get them out the way... we'd have a soldier run down with a satchel charge of explosives, swing it against the door with the time fuse on it, run back around the corner and then it'd explode and when it would the back door would blow in and the concussion would be such it would knock out everybody that was inside.'

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