The length of the battle, and casualties?

•   The battle of Somme, 1916- great war lasted between 1914-1918
  

• Overall, the first day on the Somme was a failure for the Allied forces. The British had suffered 19,240 dead, 35,493 wounded, 2,152 missing and 585 prisoners for a total loss of 57,470.[35] This meant that in one day of fighting, 20% of the entire British fighting force had been killed, in addition to the complete loss of the Newfoundland Regiment as a fighting unit. Haig and Rawlinson did not consider the enormity of the casualties and injuries from the battle, and actually considered resuming the offensive as soon as possible