Henry had approximately 5,000 archers at Agincourt, and a stock of about 400,000 arrows. Each archer could shoot about ten arrows a minute, so the army only had enough ammunition for about eight minutes of shooting at maximum fire power. However, this fire power would have been devastating. Fifty thousand arrows a minute - over 800 a second - would have hissed down on the French cavalry, killing hundreds of men a minute and wounding many more. The function of a company of medieval archers seems to have been equivalent to that of a machine-gunner, so in modern terms we can imagine Agincourt as a battle between old-fashioned cavalry, supported by a few snipers (crossbow-men) on the French side, against a much smaller army equipped with machine guns.
I once heard someone refer to the longbow as the "nuke of medieval warfare." Rees's comparison of the longbow to the machine gun is less hyperbolic than the comparison to a nuclear weapon, but both are instructive: To have seen the sky blotted out by English arrows must have been absolutely terrifying.
Via Scribal Terror