The Somme is the name of a river in northern France. The first day of the Somme offensive was the bloodiest in the history of the British Army. More than 20,000 were killed and 60,000 injured. Sixty per cent of all the officers were also killed on the first day.
The reason for the battle was that the British and French were trying (yet again) to break through the German lines. It was intended to be the winning battle. It was not and two more wearing years of war followed.