The worst part was that it was deliberate; participants describe British troops WALKING towards the German lines before being cut down - they were completely resigned. The Germans had to draw troops from the Verdun assault, and France survived to fight another day...
‘Walking as if going to the theatre’ mystified Germans noted.
British commanders promised the men that undermining and artillery would eliminate German defenses hence the casual advance. In addition each man had a 66 lb pack as he was told to take 24 hrs worth of supplies.