In the long history of the British Army, the Battle of the Somme was its bloodiest encounter. Between July 1 and mid-November 1916, 432,000 of its soldiers became casualties--about 3,600 for every day of battle. German casualties were far fewer despite British superiority in the air and in lethal artillery. What went wrong for the British, and who was responsible? Robin Prior and Trevor Wilson have examined the entire public archive on the Battle of the Somme to reconstruct the day-by-day course of the war.