We do know that the English and Welsh longbowmen used by the English Kings in the 100 years' war did train to loose their arrows at the same time to create a devastating storm of arrows effect.

Salvo fire (or loosening in this case) has been used throughout the histroy of warfare as the shock effect of massive casualties at the same time and the disorder in the ranks (especially of a moving enemy formation) is much higher with simultaneous casualties than with a steady trickle of casualties.

hi! more input on this is welcome, but meanwhile, you can get started on a couple of previous posts re volleys of arrows

• Did those showers of arrows really exist?

• Were there any archers who were trained in war to aim for individual targets as opposed to creating mass volley fire?