A Cheshire Regiment sentry in a trench near La Boisselle during the Battle of the Somme. The battle is best remembered for its first day, 1 July 1916, on which the British Army suffered 57,470 casualties, including 19,240 dead. With more than one million casualties over five months, it was one of the bloodiest battles in human history. The Allied forces attempted to break through the German lines along a 25-mile (40 km) front north and south of the River Somme.