From Wkipedia.
"Mons gained a myth, a miraculous tale that the
Angels of Mons—angelic warriors sometimes described as phantom
longbowmen from Agincourt—had saved the British Army by halting the German troops.
[67]"
A longbowman needs quite a lot of training, so wouldn't have been an instant answer. If used, I'd say they would best be used as a morale sapping thing like sniper fire. Being silent the enemy need know nothing about it until the first arrows hit. You wouldn't aim at individual soldiers, you'd send a volley of a hundred or more arrow into the trench.