In just one day almost 60,000 British soldiers were killed or wounded. Why was this first day on the Somme such a disaster for the British? World War I, trenches and barbed wire ran across the entire continent of Europe from the Mediterranean to the North Sea. At 7:30am on July 1st, 1916, after a devastating artillery bombardment lasting more than a week, 100,000 British soldiers waited in their trenches ready to advance on the German lines. They'd been told to expect minimal resistance, but as they picked their way slowly across no-man's-land, guns opened fire. Shells burst overhead, and waves of men were machine-gunned down. It was a military catastrophe of unprecedented proportions. Filmed on the battlefield itself, in laboratories and on firing ranges - archaeologists, military historians, and other experts from disciplines as diverse as metallurgy and geology investigate the factors and conduct tests to replicate and understand the factors that turned one terrible day into the bloodiest in the history of the British Army.