On 1st July 1916, after a five-day bombardment, 11 British and 5 French divisions launched their long-awaited 'Big Push' on German positions on high ground above the Rivers Ancre and Somme on the Western Front. Some ground was gained, but at a terrible cost. In killing-grounds whose names are indelibly imprinted on 20th-century memory, German machine-guns - manned by troops who had sat out the storm of shellfire in deep dugouts - inflicted terrible losses on the British infantry. Andrew Roberts evokes the pity and the horror of the blackest day in the history of the British army - a summer's day-turned-hell-on-earth by modern military technology - in the words of casualties, survivors, and the bereaved.