It was the darkest day in the history of the British Army.
In the space of just a few hours, 19,240 men were killed due to a variety of reasons.
100,000 men went 'over the top'. As they advanced they were mown down by machine gun and rifle fire. In spite of the losses, Douglas Haig, the British general, decided to continue with the attack.
Truly 'lions led by donkeys' as was said later...