V Inglefield, The History of the Twentieth (Light… (1922)
“ At 11.30 on the morning of the 7th a German aeroplane flew low over the lines. In spite of the men lying quite still the observer probably noticed the concentration of the troops, for the German guns, which had been quiet up till then, opened a heavy fire on and behind the assembly trenches, causing a certain number of casualties in the Oxford and Bucks L.I.The formation of the ground hid the opposing trenches from view—a factor of great importance, for it made the task of cutting the enemy wire a most difficult one for the artillery. ”
