At 0720 on 1 July 1916 two great mines either side of La Boisselle were exploded. At 0730 the order was given for 16,000 British troops to go over the top and advance down Tara and Usna hills into the ‘Sausage’ and ‘Mash’ valleys towards the German line. By 0740 13,000 of them had been cut down by machine gun fire.